The on Line Mud Logging Handbook USA

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The On-line Mud Logging Handbook Alun Whittaker
This is Page 1 of Chapter 8: Hdro!arbon "#aluation Find Another Page Find Another Chapter
The On-line
The On-line
Mud Logging
Mud Logging
Handbook
Handbook
by Alun Whittaker by Alun Whittaker
See Acrobat Document Properties
in the Acrobat !eader " #ile menu$
%or publication and re&ision dates
Hydrocarbon '&aluation
Hydrocarbon '&aluation
- Oil( )as( *
- Oil( )as( *
Precursors
Precursors
Aegis $roup
%&& Ohio 'treet
(alle)o* CA +&,+--,-,1
.'A
[email protected] [email protected]
The On-line Mud Logging Handbook Alun Whittaker
Hydrocarbon '&aluation + Oil( )as * Precursor
Mud logging ,as born as a ,ell-site e-tension o% petroleum laboratory analysis. /t is logical that modern mud logging should include( ,here
cost 0usti%ies( ,ell-site application o% other( ne,er laboratory geo-chemical tests and analyses. !ecent ad&ances in solid state electronics
ha&e %inessed the Mud Logging Golden Rules by allo,ing the de&elopment o% analytical hard,are that is smaller( more rugged( easier(
and less time consuming to operate + also much cheaper to buy and use. Techni1ues in use include2
✔ 'nhance hydrocarbon gas analyses
✔ 3uttings testing %or oil( gas and chemical signs
✔ Total Organic 3arbon in kerogen( pyro-analysis( and other source bed geo-chemical tools
✔ Oil %luorescence( contaminants and 1uantitati&e %luorimetry
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The On-line Mud Logging Handbook Alun Whittaker
Table o% 3ontents
Geo-chemistry in Work Gloves.......................................................................................................................................................................4
Hydrocaron Gas Analysis...........................................................................................................................................................................56
Cuttings !valuation.......................................................................................................................................................................................57
'arly Signs..................................................................................................................................................................................................57
Petroleum Odors....................................................................................................................................................................................57
Oil Pops..................................................................................................................................................................................................58
!ainbo, and Sheen...............................................................................................................................................................................58
Detailed '-amination..................................................................................................................................................................................58
"il Fluorescence............................................................................................................................................................................................59
Mineral #luorescence..................................................................................................................................................................................:6
Petroleum Product #luorescence................................................................................................................................................................:5
Mud Additi&es.........................................................................................................................................................................................:5
Oil-base * Additi&es...............................................................................................................................................................................:5
Pipe Dope...............................................................................................................................................................................................:5
Sol&ent 3ut Test..........................................................................................................................................................................................::
3ut Speed..............................................................................................................................................................................................:;
3ut <ature..............................................................................................................................................................................................:;
3ut 3olors..............................................................................................................................................................................................:;
#ample !$amination Procedure...................................................................................................................................................................:=
Mud Oil Sho, Tests....................................................................................................................................................................................:>
?n,ashed 3uttings Oil Sho, Tests............................................................................................................................................................:4
Automated Fluorimetry .................................................................................................................................................................................;5
Re%ractometry................................................................................................................................................................................................;4
Wellsite Geo-chemistry.................................................................................................................................................................................7:
Total Organic 3arbon..................................................................................................................................................................................77
Pyro-analysis..............................................................................................................................................................................................79
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The On-line Mud Logging Handbook Alun Whittaker
Temperature Programmed 3hromatography...............................................................................................................................................=9
Pyro-chromatography..................................................................................................................................................................................=4
Worst Case #cenario.....................................................................................................................................................................................95
&he #'an #ong..............................................................................................................................................................................................9;
And (e$t.........................................................................................................................................................................................................9;
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The On-line Mud Logging Handbook Alun Whittaker
Didn@t %ind ,hat you needed hereA Sorry.
Why not go back to the Chapter #ummaries( and %ine a better place to start( or use the )nde$ to search %or the sub0ect you need.
List o% #igures * Tables
#igure 52 A chromatogram containing su%%icient components in characteristic proportions may be as uni1ue as a %inger print in correlating
migrated or accumulated hydrocarbons. These chromatograms are %rom kno,n( pure samples o% producing Bones C5( C:( and %rom a real-
,orld some,hat contaminated and degraded$ oil-based drilling %luid.............................................................................................................55
#igure :2 These chromatograms are %rom kno,n( a pure sample o% producing Bones C5( %rom the real-,orld( oil-based drilling %luid( and %rom
t,o di%%erent composition mi-tures o% the t,o..................................................................................................................................................5:
#igure ;2 These chromatograms are %rom kno,n( a pure sample o% producing Bones C:( %rom the real-,orld( oil-based drilling %luid( and %rom
t,o di%%erent composition mi-tures o% the t,o..................................................................................................................................................5;
#igure 72 3onsisting o% homologous series or %amilies o% hydrocarbons ranging in molecular ,eight( physical and chemical properties o% a
crude oil is a re%lection o% itDs chemical composition. Density( &iscosity( natural and %luorescence colors o% a crude oil( and itDs associated gas
re%lect the distribution o% molecular ,eight homologs o% compounds in the mi-ture. .......................................................................................54
#igure 82 #luorescent minerals commonly %ound in ,ell cuttings.....................................................................................................................:6
#igure =2 #luorescence and cut testing %or oil must be per%ormed in a rigorous and systematic manner in order to a&oid erroneous
interpretations( missed sho,s or %alse alarms. ...............................................................................................................................................:7
#igure 92 '&aluation o% mud and cuttings %or signs o% oil or residuum should be per%ormed routinely( Appro-imately once each hour in all
%ormations. /n potential or actual reser&oir rocks( the smallest possible sample inter&al should be used. .......................................................:9
#igure >2 Euantitati&e #luorescence intensity impro&es correlation o% sho, 1uality bet,een Bones. On a computer-generated mud log( both
intensity( and color-coded appro-imation o% %luorescent color helps illustrate both the oil sho, 1uality and type.............................................;:
#igure 42 A %luoro-spectrometer can detect 1uantitati&e %luorescence at a range o% e-citation ,a&e lengths...................................................;;
#igure 562 Euantitati&e %luorescence using a scanning spectrometric ............................................................................................................;7
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The On-line Mud Logging Handbook Alun Whittaker
#igure 552 Euantitati&e %luorescence using a synchronous scanning spectrometry plotted as t,o-dimensional contour plot. <ote that the
colors used represent( gradations o% %luorescent intensity( and not %luorescence color as sho,n in #igure >$. When setting up a computer
plotter to create a contour plot o% this this type( you should take care to select colors or te-tures %rom the de&ice@s palette that cannot be
misunderstood. ...............................................................................................................................................................................................;=
#igure 5:2 Well-to-,ell correlation using a E#T %luorescence log....................................................................................................................;9
#igure 5;2 This Atago hand re%ractometer is made in Fapan and is not surprisingly$ compact( reliable and reasonably priced. <eed / say
moreA..............................................................................................................................................................................................................76
#igure 572 !e%ractometry ,as de&eloped %or use in petro-chemistry and %ood technology to determine oil purity %rom a measurement o%
!e%racti&e /nde-. This empirical relationship bet,een !e%racti&e /nde- and AP/ )ra&ity o% crude oil gi&es reasonable accuracy e&en ,hen
the oil base type is unkno,n. ..........................................................................................................................................................................75
#igure 582 The L'3OG 3!-5: Total Organic 3arbon TO3$ analyBer pro&ides the basic geo-chemical measurement used to indicate source
bed 1uality and against ,hich to normaliBe all other geo-chemical measurements. /llustration courtesy o% 'HLO)( /nc.$.............................7;
#igure 5=2 Total Organic 3arbon content and source bed 1uality %or argillites claystones and shales$ and carbonate rocks limestones(
dolomites and calcareous mudstones$. ..........................................................................................................................................................78
#igure 592 Total Organic 3arbon pro&ides a reliable 1uantitati&e estimate o% the richness o% organically-deri&ed carbon. ?n%ortunately it
cannot indicate the type or present diagenetic state o% the organic material ,ithout additional geo-chemical or mud logging data. ...............7=
#igure 5>2 The !ock-'&al pyro-analyBer heats a cuttings sample in a helium atmosphere( detects %ree hydrocarbons( kerogen abundance(
type and maturity. ...........................................................................................................................................................................................7>
#igure 542 !esults %rom the !ock-'&al pyro-analyBer indicate the presence o% %ree hydrocarbons( and the abundance( type and maturity o%
kerogen %rom the parameters S5( S:( S; and Tma-. ......................................................................................................................................86
#igure :62 The S: peak alone is a measure o% potential hydrocarbon yield o% the ,hole rock.........................................................................8:
#igure :52 The S: and S; peaks together ,ith the TO3 &alue are a measure o% kerogen type and maturity..................................................8;
#igure ::2 The Ian Jre&elen diagram relates Hydrogen /nde- S:KTO3$ and O-ygen /nde- S;KTO3$ ,ith source type and maturity...........87
#igure :;2 The relati&e richness o% Hydrogen re%lected in the S: peak$ and O-ygen re%lected in the S; peak$ in the kerogen is diagnostic o%
the type and yield o% hydrocarbons to be e-pected %rom it...............................................................................................................................88
#igure :72 #rom correlation ,ith the /#P database( Tma- can be used to indicate maturity o% the source bed ...............................................8=
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The On-line Mud Logging Handbook Alun Whittaker
#igure :82 The Well-site geo-chemistry Log displays !ock '&alG pyro-Analysis( TO3 or associated mud log and geo-chemical data and may
be used to monitor source rock and reser&oir occurrence( type and maturity. ................................................................................................89
#igure :=2 The !ock-'&al source bed e&aluation may be modi%ied by the presence o% other non-source materials( such as catalytic( high
3'3 smectite clays that can enhance reaction in the !ock-'&al o&en( increasing hydrocarbon yield( or achie&ing peak hydrocarbon
e&olution at a lo,er Tma-. ..............................................................................................................................................................................8>
#igure :92 The !ock-'&al source bed e&aluation may be modi%ied by the presence o% other non-source materials( such as unstable
3arbonates. These may initiate decomposition o% stable carbonates at lo,er temperatures( causing a %alsely higher and ,ider S; peak( and
a pessimistic O-ygen /nde-.............................................................................................................................................................................84
#igure :>2 The !ock-'&al source bed e&aluation may be modi%ied by the presence o% other non-source materials( such as dense( in&olatile
bitumens resulting in ,idened( and partially merged S5 and S: peaks. .........................................................................................................84
#igure :42The L'3O 3!-5: measures only total organic carbon TO3$ in the source rock............................................................................=6
#igure ;62 The !ock-'&al / and // di%%er only in electronics and processor design. The measurements are essentially the same2 S5( S:( S;
peaks and temperature Tma-..........................................................................................................................................................................=5
#igure ;52 The Oil Sho, AnalyBer( or !ock-'&al ///( measures 3arbon Dio-ide %or total organic carbon TO3$ content( and not %or kerogen
O-ygen /nde-..................................................................................................................................................................................................=5
#igure ;:2 The Thermolytic Hydrocarbon AnalyBer is a simpli%ied pyro-analyBer( indicati&e o% ,hat may become the ne-t generation mud
logging analyBer...............................................................................................................................................................................................=:
#igure ;;2 The Pyrologger is a another candidate to be the ne-t generation mud logging analyBer...............................................................=:
#igure ;72 Measured and computed parameters a&ailable %rom the programmable !ock-'&al =....................................................................=7
#igure ;7 continued$2 Measured and computed parameters a&ailable %rom the programmable !ock-'&al =.................................................=8
#igure ;7 continued$2 Measured and computed parameters a&ailable %rom the programmable !ock-'&al =.................................................==
#igure ;82 Temperature-programmed chromatography can pro&ided e-tended hydrocarbon analyses allo,ing recognition o% reser&oir
character and producti&ity( %or e-ample( petroleum condensate or ,et gas....................................................................................................=9
#igure ;=2 Temperature-programmed chromatography o% a high gra&ity light and &olatile$ oil. ......................................................................=>
#igure ;92 Temperature-programmed chromatography o% a lo, gra&ity dense and hea&y$ oil........................................................................=>
#igure ;>2 Temperature-programmed chromatography o% a &ery dense( immo&able residual oil.....................................................................=>
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#igure ;42 A pyro-chromatogram o% the S5 peak %rom a pyroliBed source bed sample. .................................................................................96
#igure 762 A %ragmentogram o% the S: peak %rom a pyroliBed source bed sample. .........................................................................................96
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The On-line Mud Logging Handbook Alun Whittaker
Hydrocarbon '&aluation + Oil( )as * Precursors
)eo-chemistry in Work )lo&es
Mud logging in&ol&es the analysis o% organic and petroleum material %rom drilling %luids and rocks. So does petroleum geo-chemistryL Most
mud loggers donDt ha&e Ph.D.Ds( but some o% the best ones do. Many petroleum geo-chemists do ha&e doctorates( although some &ery good
ones donDt.
The di&iding line bet,een mud logging and petroleum geo-chemistry is an arbitrary and( to my mind( a 1uite unnecessary one. /t allo,s
some narro,-minded geo-chemists to sustain an absurd snobbery. /t also allo,s some in%erior mud loggers to a&oid applying rigorous
scienti%ic standards to their ,ork. The only real di%%erence is that2
✔ Mud logging measurements are commonly targeted at tactical( real time problems in&ol&ing real hydrocarbons( usually in e-isting
reser&oirs( ,hile
✔ Petroleum geo-chemistry measurements are o%ten used to address strategic( historical problems in&ol&ing source beds and migration
path,ays.
/n reality( as ,e has already begun to see( both kinds o% data can contribute to either kind o% problem. So ,e are le%t ,ith the only real
di%%erence being that geo-chemical analytical instruments are more e-pensi&e( and less suited to use at the ,ell site( and e&en that
di%%erence( as ,eDll see in this chapter( is starting to go a,ay.
Moth mud logging and petroleum geo-chemistry in&ol&e the e-traction( separation( and identi%ication o% hydrocarbon components using
organic chemical methods. /n reality( any laboratory geo-chemical procedure that may be applied in real-time at the ,ell site can be added
to the suite o% mud logging ser&ices( i% it complies ,ith mud logging golden rule numer one N it can be carried out ,ithout placing too
great an e-tra strain on the mud loggersD time and attention. /n recent years( impro&ement and simpli%ication o% sample processing
procedures and the de&elopment o% reliable( robust( semi-automated analyBers ha&e allo,ed a number o% procedures to make this
transition.
The %irst o% these ,as gas chromatography ,hich is used to separate the indi&idual hydrocarbons %or more precise analysis. The
techni1ue( %irst introduced in the %i%ties( is no, standard in &irtually
all modern mud logging units.
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In Datalog’s GC-TRACER (see In Datalog’s GC-TRACER (see Chapter 5 Chapter 5), the chromatograph has even ), the chromatograph has even
gone beyond the md logg!ng n!t, to the md "lo# l!ne !tsel"$ gone beyond the md logg!ng n!t, to the md "lo# l!ne !tsel"$
The On-line Mud Logging Handbook Alun Whittaker
Techni1ues that ha&e more recently made the transition to ,ell-site application include pyro-analysis( in ,hich petroleum oils and
precursors are thermally decomposed in an inert atmosphere. Analysis o% the gaseous products o% this thermal cracking yields in%ormation
on the richness( maturity and e&entual products o% organic source material in the geological section.
More recently( optical techni1ues( such as re%ractometry and %luorimetry no, make it possible to determine something o% the physical
properties o% oil %rom the small amounts reco&ered in cuttings ,hile drilling.
The ne,est addition to ,ell-site geo-chemical ser&ices in&ol&es the combination o% pyrolysis techni1ues ,ith chromatography. 3ontrolled
progressi&e heating cracks and &olatiliBes oil and source material ,hich is then separated in a heated chromatograph column. A techni1ue
that has been long used in the laboratory( this type o% instrumentation has no, been made in a compact con%iguration suitable to the logging
unit and automated to allo, rapid analyses to be per%ormed.
The selection o% ser&ices in a drilling operation should not be made on the basis o% ,hether mud logging or ,ell-site geo-chemistry is
re1uired. /nstead( the decision should be made on the basis o%2
✔ What in%ormation is re1uired(
✔ When is it re1uired( and
✔ 3an this schedule be met more reliably and economically2
✔ /n the ,ell-site mud logging unit( or
✔ At an o%%-site laboratory.
Hydrocarbon )as Analysis
The simplest %orm o% geo-chemical analysis is nothing more than a re&ersion to the earliest o% mud logging techni1ues2 container head-
space analysis. This type o% analysis is not normally per%ormed on e&ery sample caught. Pre%erence is gi&en to samples caught %rom Bones
o% particular interest( and samples may be allo,ed to back-up %or analysis ,hen time is a&ailable.
/nstead o% using the gas trap( a standardiBed gas sample is ,ithdra,n %rom a blender( or a sealed sample container( at a controlled pressure
and temperature. To do this( canned samples o% mud and cuttings
can be care%ully punctured and then re-sealed ,ith a rubber
septum. A syringe is then used to e-tract a measured &olume o%
gas to be in0ected into a chromatograph.
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%amples may also be e&tracted "rom the canned ctt!ngs and md, s!ng %amples may also be e&tracted "rom the canned ctt!ngs and md, s!ng
a md (steam or vacm) st!ll ' bt th!s !s a a md (steam or vacm) st!ll ' bt th!s !s a compl!cat!on #!th l!ttle compl!cat!on #!th l!ttle
bene"!t( bene"!t(
The On-line Mud Logging Handbook Alun Whittaker
The chromatograph is similar to the type used in regular mud logging e-cept that is has a heated( manual sample in0ection port( to keep the
sample &olatile( and not condense be%ore getting into the chromatograph column. The column material( temperature and carrier gas %lo,
rate are also optimiBed %or the separation and detection o% hea&ier &olatile hydrocarbons. <ot being bound by real-time logging priorities( the
analysis may be allo,ed to run longer in order to identi%y alkanes as hea&y as Duo-decane 3
5:
H
:=
$ ,ith good peak separation and ase-
line resolution.
This type o% chromatography is used as a supplement to( not a replacement %or con&entional mud logging chromatography. /tDs
impro&ements in analytical accuracy are gained only at the e-pense o% loss o% timeliness more time is needed to process each sample$ and
loss o% &ertical resolution in the log less samples can be processed in the time a&ailable at the ,ell site( although some may be held back
%or later processing to %ill in detail as re1uired$. /t is in %act a &ery use%ul tool %or correlation o% hydrocarbons bet,een di%%erent reser&oirs(
recognition o% migration path,ays or discrimination or %ormation %luids masked by oil-based drilling muds.
#igure 52 A chromatogram containing su%%icient components in characteristic proportions may be as uni1ue as a %inger
print in correlating migrated or accumulated hydrocarbons. These chromatograms are %rom kno,n( pure samples o%
producing Bones C5( C:( and %rom a real-'orld some,hat contaminated and degraded$ oil-based drilling %luid.
Although the alkanes are an homologous series( and commonly occur together( any mi-ture ,ill contain a uni1ue selection and distribution
o% compounds. A chromatogram ,ith enough components and good enough resolution can be used to recogniBe characteristic combinations
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The On-line Mud Logging Handbook Alun Whittaker
and proportions o% compounds. This is illustrated in Figure *( Figure +( and Figure ,( in ,hich chromatograms %rom t,o di%%erent( kno,n
petroleum reser&oirs( and %rom a sample o% the base oil used to build an oil-based drilling %luid can be used to identi%y a ne,ly disco&ered
reser&oir( penetrated using this oil-based mud. 'lectronically subtracting the drilling mud chromatogram %rom that o% the mi-ture lea&es
behind a chromatogram containing the same components in the same proportions as in the reser&oir. We are able to remo&e the e%%ect o%
the mud contamination( and demonstrate a relationship bet,een a ne,ly-drilled reser&oir and a kno,n pre&iously-drilled reser&oir. This type
o% mathematical treatment may also be applied to the routine chromatogram but the greater the number o% components( the greater ,ill be
the reliability and discriminatory po,er o% the techni1ue.
#igure :2 These chromatograms are %rom kno,n( a pure sample o% producing Bones C5( %rom the real-'orld( oil-based
drilling %luid( and %rom t,o di%%erent composition mi-tures o% the t,o.
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The On-line Mud Logging Handbook Alun Whittaker
'lectronically subtracting a multiple o% the drilling mud chromatogram lea&es behind a chromatogram containing the same components in
the same proportions as in Reservoir -*. We are able to remo&e the mud contamination and demonstrate a relationship bet,een the
present and one o% the older reser&oirs.
#igure ;2 These chromatograms are %rom kno,n( a pure sample o% producing Bones C:( %rom the real-'orld( oil-based
drilling %luid( and %rom t,o di%%erent composition mi-tures o% the t,o.
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The On-line Mud Logging Handbook Alun Whittaker
3uttings '&aluation
/n Chapter .( ,e re&ie,ed the collection( preparation and inspection o% cuttings %or lithological and mineralogical e&aluation.
There are a number o% additional procedures in standard( descripti&e mud logging %or the e&aluation o% li1uid and solid hydrocarbons2 oils(
tars( and ,a-es in cuttings.
Me%ore mo&ing on to geo-chemical procedures carried out at the ,ell site or in the laboratory( on un,ashed cuttings( ,eDll look at the
additional steps in routine mud logging sample e-amination %or e&aluating an oil bearing sample. The most important o% these is the
recognition( and use o% oil %luorescence.
'arly Signs
?se your eyes( your noise and anything else a&ailable. The %irst indications o% the presence o% oil in a ,ell-site sample begin in the sample
catching and preparation stages.
Petroleum Odors
At the shale shaker( there are usually pre&ailing smells o% drilling mud and e-haust %rom motors around the rig( <e&ertheless( it is possible to
detect the cleaner( s,eeter odor o% crude oil carried in cuttings on the shaker screens.
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It !s common "or re"erence boo)s to descr!be crde o!l as hav!ng a pa!nt-l!)e odor( I have smelled many types o" pa!nt( It !s common "or re"erence boo)s to descr!be crde o!l as hav!ng a pa!nt-l!)e odor( I have smelled many types o" pa!nt(
They all have d!""erent odors and none o" them, !n my e&per!ence, has a smell that !s anyth!ng l!)e that o" crde o!l( I They all have d!""erent odors and none o" them, !n my e&per!ence, has a smell that !s anyth!ng l!)e that o" crde o!l( I
can also say that crde o!l does not have the acr!d or b!tter odor commonly assoc!ated #!th re"!ned o!l or gasol!ne( can also say that crde o!l does not have the acr!d or b!tter odor commonly assoc!ated #!th re"!ned o!l or gasol!ne(
Commonly conta!n!ng more aromat!cs (l!terally and descr!pt!vely) and more volat!les than re"!ned prodcts, crde o!l Commonly conta!n!ng more aromat!cs (l!terally and descr!pt!vely) and more volat!les than re"!ned prodcts, crde o!l
can best be descr!bed as hav!ng a s#eeter, more pleasant, perhaps even sl!ghtly "r!ty odor( can best be descr!bed as hav!ng a s#eeter, more pleasant, perhaps even sl!ghtly "r!ty odor(
Remember that, be"ore md logg!ng, #ell-s!te geolog!sts #ere n!c)named Remember that, be"ore md logg!ng, #ell-s!te geolog!sts #ere n!c)named Shale Sniffer s Shale Sniffer s ( At other t!mes, they #ere even called ( At other t!mes, they #ere even called
Shale Eater s Shale Eater s, becase !t #as cla!med that even the sl!ghtest o!l trace cold be tasted by plac!ng a ctt!ng on the tonge( , becase !t #as cla!med that even the sl!ghtest o!l trace cold be tasted by plac!ng a ctt!ng on the tonge(
Another tr!c) #as to gr!nd a ctt!ng bet#een the teeth ' a sensat!on o" gr!tt!ness cold help d!scr!m!nate a s!ltstone Another tr!c) #as to gr!nd a ctt!ng bet#een the teeth ' a sensat!on o" gr!tt!ness cold help d!scr!m!nate a s!ltstone
(conta!n!ng "!ne clast!c mater!al) "rom claystone (#!th pre clay m!nerals)( *h!le I don’t recommend e!ther o" these as a (conta!n!ng "!ne clast!c mater!al) "rom claystone (#!th pre clay m!nerals)( *h!le I don’t recommend e!ther o" these as a
standard pract!ce, I can test!"y that they both #or)( standard pract!ce, I can test!"y that they both #or)(
The On-line Mud Logging Handbook Alun Whittaker
Petroleum odors may also be detected on ,ashed cuttings( particularly as they are ,armed in the sample dryer( or by the heat o% the
microscope illuminator.
Oil Pops
When catching a pan %ull o% cuttings %or bagging un,ashed samples( you may notice small droplets or globules o% oil popping out o% the
coating o% drilling %luid on the cuttings. These may become e&en more &isible ,hen the mud is diluted ,hile you are ,ashing the cuttings.
!ainbo, and Sheen
A sheen or rainbo,-like luster may %irst be identi%ied on the mud coated cuttings on the shale shaker( or e&en on the mud itsel% in the
possum belly ditch( and running o%% belo, the shale shaker. The sheen may become more &isible on the ,ater running o%% ,hile ,ashing( or
on the sur%ace o% ,et cuttings in the sie&e. The sheen can be more apparent in bright outdoor sun light( than in the more uni%orm( less
intense( %luorescent lights inside the mud logging unit( or shale shaker house.
Al,ays check the mouth o% blender 0ar( a%ter running the blender test both %or petroleum odors and %or a rainbo, sheen on the ,ater sur%ace.
The mud logger should be a,are o%( and looking %or all o% these signs all o% the time. When using oil-based drilling %luid or additi&es( some o%
these signs may be obser&ed in e&ery sample.
/% so( that should be noted and described on the mud log ,orksheet2
✔ To pre&ent later( o%%-site obser&ers o% samples %rom dra,ing %alse conclusions( and
✔ To establish a baseline oil trace description( against ,hich %uture genuine oil sho,s can be 0udged.
Detailed '-amination
/n addition to looking %or %irst signs( there is a series o% detailed e-aminations and oil tests that must be per%ormed on e&ery sample ,hen
conditions indicate the possibility o% an oil Bone or potential oil Bone$ ha&ing been penetrated( such as2
✔ A drilling break(
✔ 'arly signs( such as petroleum odor( oil popping( or sheen(
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I" #e see cles that o!l may present, then #e mst search d!l!gently to con"!rm that presence( I" #e see cles that o!l may present, then #e mst search d!l!gently to con"!rm that presence(
Conversely, #hen #e dr!ll !nto a potent!al reservo!r bt see no obv!os "!rst s!gns o" the Conversely, #hen #e dr!ll !nto a potent!al reservo!r bt see no obv!os "!rst s!gns o" the
presence o" o!l, then #e mch search e+ally d!l!gently to con"!rm, and e&pla!n that absence( presence o" o!l, then #e mch search e+ally d!l!gently to con"!rm, and e&pla!n that absence(
The On-line Mud Logging Handbook Alun Whittaker
✔ A gas sho, consisting o% an increase in total combustible hydrocarbons(
✔ A gas sho, ,ith the %irst appearance o% hea&ier alkanes Propane( Mutanes( and Pentanes$ in the hydrocarbon chromatogram( or an
increase in their concentration( relati&e to that o% the lighter
alkanes Methane and 'thane$(
✔ A change in cuttings lithology ,ith the appearance o%
potential reser&oir rock types( such as %ine( unconsolidated
sandstone( or porous limestone( or
✔ /denti%ication o% the top depth or lithological boundary$ o% a %ormation ,hich the ,ell prognosis or mud logging instructions$ indicates
to be a Bone o% interest.
/n this Bone( samples %or oil testing should be caught as o%ten as possible no less o%ten than every */ minutes$ and( i% necessary( labeled
by depth( and then set aside to back up %or later e-amination. 3ontinue to catch( process and package other sets un,ashed( rinsed(
,ashed and dried( and so on$ on their normal schedule.
#or each oil e&aluation( the %ollo,ing samples are re1uired2
✔ #resh drilling mud
✔ #resh un,ashed$ cuttings
✔ Washed and sie&ed cuttings
✔ Mlender residue
✔ Diluted mud
✔ 3rushed cuttings
'ach o% these samples must be e-amined ,hile %resh N old( dried( cuttings samples are o% little &alue in oil e&aluation. /%( a%ter the %act( your
inspection o% ,ashed and dried samples does not agree ,ith %resh( ,ell-site obser&ations reported on the mud log( it is probably better to
trust the %resh obser&ations o&er your o,nL
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The al)anes that const!tte the ma,or!ty o" hydrocarbons !n a petrolem The al)anes that const!tte the ma,or!ty o" hydrocarbons !n a petrolem
reservo!r are an homologos ser!es, vary!ng progress!vely and pred!ctably reservo!r are an homologos ser!es, vary!ng progress!vely and pred!ctably
!n phys!cal and chem!cal propert!es "rom the l!ghtest (-ethane) to the !n phys!cal and chem!cal propert!es "rom the l!ghtest (-ethane) to the
heav!est (petrolem #a&es and tars)( The compos!t!on o" a reservo!r "l!ds heav!est (petrolem #a&es and tars)( The compos!t!on o" a reservo!r "l!ds
!s s!m!larly progress!ve "rom l!ghtest to heav!est components( I" heavy !s s!m!larly progress!ve "rom l!ghtest to heav!est components( I" heavy
al)anes (o!ls) become present !n the reservo!r, then med!m al)anes al)anes (o!ls) become present !n the reservo!r, then med!m al)anes
(heav!er gases) #!ll also be added to the m!&tre( Th!s !s d!scssed !n more (heav!er gases) #!ll also be added to the m!&tre( Th!s !s d!scssed !n more
+ant!tat!ve deta!l !n +ant!tat!ve deta!l !n Chapter 13 Chapter 13( (
The On-line Mud Logging Handbook Alun Whittaker
'ach o% them should be e-amined2
✔ With the naked eye and the microscope(
✔ /n &isible and ultra&iolet light( and
✔ While ,et( dry and treated ,ith an organic sol&ent( or hot ,ater.
Any &isible traces o% oil( tar or residuum on the cuttings( or in the ,ater must be reported on the mud log ,orksheet. All samples( regardless
o% ,hether &isible staining is obser&ed( must be processed through the %ollo,ing %luorescence( sol&ent cut and e-amination procedures( and
the results %ully documented. /n a potential reser&oir( is as important to report negati&e results( as positi&e ones.
Oil #luorescence
Luminescence is a common property in nature. Molecules o% many compounds ,ill absorb electromagnetic radiation in%rared( &isible(
ultra&iolet light( and so on$( at one or more characteristic e$citation 'avelengths and( as a result( some o% their bond electrons absorb
energy( and mo&e to a higher energy le&el orbital. The molecule is less stable in this e-cited state( and so the electrons soon %all back to
their original energy le&el ,ith the re-emission o% electromagnetic energy. This emission is commonly not at the original e-citation
,a&elengths( but at a di%%erent( but e1ually characteristic( longer emission 'avelength see Whittaker0 *12/$.
/n some cases( the molecule in an e-cited state is meta-stale( and so the emission o% energy is slo, and may continue %or some time a%ter
the e-citation energy source is remo&ed. 3ompounds that beha&e
in this manner are said to be phosphorescent.
A phosphorescent compound ,ill( a%ter e-citation( continue to
emit energy %or some time a%ter,ards.
/n other compounds( the e-cited state is much less stable.
'mission begins rapidly a%ter e-citation( and continues only so
long as the e-citation source is acti&e. These are called
%luorescent compounds.
There are numerous %luorescent compounds commonly %ound in
crude petroleum ,ith a ,ide range o% characteristic pairs o%
e-citation and emission ,a&elengths. ?n%ortunately( there are
other( e1ually common( naturally occurring %luorescent minerals to
be %ound in cuttings samples see belo,$.
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A system !s sa!d to be meta-stable #hen !t e&!sts !n a state o" psedo- A system !s sa!d to be meta-stable #hen !t e&!sts !n a state o" psedo-
e+!l!br!m, sch that !t has a "ree energy h!gher than that o" the tre e+!l!br!m, sch that !t has a "ree energy h!gher than that o" the tre
e+!l!br!m state( A metastable system #!ll not spontaneosly nor rap!dly e+!l!br!m state( A metastable system #!ll not spontaneosly nor rap!dly
change( Instead, !t #!ll do so slo#ly or !nterm!ttently over a per!od o" change( Instead, !t #!ll do so slo#ly or !nterm!ttently over a per!od o"
t!me, or nder the !n"lence o" e&ternal st!mlants( .or e&ample, a"ter t!me, or nder the !n"lence o" e&ternal st!mlants( .or e&ample, a"ter
e&c!tat!on by dayl!ght, the lm!nos hands o" an alarm cloc) #!ll e&c!tat!on by dayl!ght, the lm!nos hands o" an alarm cloc) #!ll
cont!ne to em!t l!ght all n!ght, bt !" sht a#ay !n a dar) cpboard, they cont!ne to em!t l!ght all n!ght, bt !" sht a#ay !n a dar) cpboard, they
#!ll eventally dar)en and rema!n dar) nt!l, one aga!n, broght ot #!ll eventally dar)en and rema!n dar) nt!l, one aga!n, broght ot
!nto the l!ght( !nto the l!ght(
The On-line Mud Logging Handbook Alun Whittaker
The most use%ul %luorescent crude oil components to mud logging( are a number o% poly-cyclic multi-ringed$ aromatic( and alicyclic
compounds that are common in almost all petroleum oils and ,hich( ,hen e-cited by shorter ,a&elength ultra-&iolet light :66 nanometers
or less$( strongly %luoresce in the &isible spectrum.
The ,a&elength o% the %luorescence to ,hich a compound is susceptible is closely related to the molecular ,eights o% the %luorescing
compounds see 3orden 4 Campell0 *125( and Lynch0 *16+$. Once again( the %amilial nature o% hydrocarbon compositions( is re%lected in
the range and distribution o% molecular ,eights in the oil and the o&erall density or gra&ity$ o% the mi-ture. Within bounds( controlled by
e-tremes o% base chemistry2
✔ Lo, gra&ity or denser$ oils %luoresce at longer( in%rared( red and orange( &isible ,a&elengths( ,hile
✔ Lighter( high gra&ity oils ,ill %luoresce at shorter( yello, or blue( &isible ,a&elengths #ee Figure 5$.
The ultra-&iolet black light$ inspection bo- is ubi1uitous in mud
logging units.
The usual con%iguration is a light-tight( black-lined bo- that can
be illuminated internally ,ith either natural ,hite( or ultra&iolet
light. The bo- usually has light-tight %le-ible doors at each side
so that a large ob0ect( such as a core can be passed through
the light bo-. They also allo, the mud logger to manipulate
samples( test tools( and chemicals inside the bo-.
An alternati&e consists o% a con&entional binocular microscope ,ith an enclosed stage and an illuminator capable o% supplying both ,hite
and ultra-&iolet light.
Another use%ul option is a battery-po,ered( portable ?I light( that can be taken %rom the unit to the core processing area or e&en the shale
shaker to e-amine %luorescence.
All o% these designs ha&e ad&antages and probably all three should be carried in a ,ell e1uipped mud logging unit. /t is essential to ha&e a
means o% illuminating and magni%ying oil stains ,ithin the
pore spaces and sur%aces o% a single cuttings. On the other
hand( an enclosure large enough to accommodate something
as large as a piece o% core is also needed. #inally( %or
inspecting ,hole core( or large &olumes o% mud and cuttings
at the shale shaker( a portable unit can be &ery use%ul.
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In /010, a md logger2s ltrav!olet !nspect!on bo& ach!eved the db!os In /010, a md logger2s ltrav!olet !nspect!on bo& ach!eved the db!os
honor o" be!ng the only md logg!ng !nstrment to appear !n a 3layboy honor o" be!ng the only md logg!ng !nstrment to appear !n a 3layboy
center"old$ 4o, I’m sorry, I don’t remember #h!ch month (Try center"old$ 4o, I’m sorry, I don’t remember #h!ch month (Try Googl-ing Googl-ing
that one)( that one)(
Tal)!ng o" mov!es, hand-held, ltra-v!olet !llm!nators have become eas!er, Tal)!ng o" mov!es, hand-held, ltra-v!olet !llm!nators have become eas!er,
and cheaper to get hold o", ever s!nce they have become so common on T5 and cheaper to get hold o", ever s!nce they have become so common on T5
cr!me sho#s, sed along #!th cr!me sho#s, sed along #!th luminol luminol , to h!ghl!ght tell-tale traces o" blood , to h!ghl!ght tell-tale traces o" blood
and ((( other st""((( at cr!me scenes( *hy #old #atch!ng someth!ng l!)e and ((( other st""((( at cr!me scenes( *hy #old #atch!ng someth!ng l!)e
that !nsp!re someone #ant to by one a Rad!o %hac)6 *ho )no#s6 that !nsp!re someone #ant to by one a Rad!o %hac)6 *ho )no#s6
The On-line Mud Logging Handbook Alun Whittaker
#igure 72 3onsisting o% homologous series or %amilies o% hydrocarbons ranging in molecular ,eight( physical and
chemical properties o% a crude oil is a re%lection o% itDs chemical composition. Density( &iscosity( natural and
%luorescence colors o% a crude oil( and itDs associated gas re%lect the distribution o% molecular ,eight homologs o%
compounds in the mi-ture.
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The On-line Mud Logging Handbook Alun Whittaker
Mineral #luorescence
?n%ortunately( crude oil is not the only material %ound in ,ell cuttings that %luoresces under ultra&iolet light. The most common source o%
%luorescence in cuttings are rocks and minerals. #ortunately( although ,idespread( the %luorescence colors are subdued and the intensity
lo,. 3ommon e-amples are sho,n in Figure /.
Mineral or ro!k tpe "2ission fluores!en!e !olor
3olo2ite and Magnesian Li2estone 4ello5* ello5ish-bro5n to dark bro5n
Aragonite and Cal!areous 2udstones 4ello5-5hite to pale bro5n
Chalk Li2estone Purple
6oliated 7Paper8 'hale Tan to graish-bro5n
Anhdrite 9lue to 2id-gra
Prite Mustard ello5 to greenish-bro5n
#igure 82 #luorescent minerals commonly %ound in ,ell cuttings.
#luorescence o% these colors and intensity are unlikely to be mistaken %or a true oil sho, but the background o% mineral %luorescence behind
an oil sho, may modi%y the color and intensity( and so complicate comparati&e estimates. /t is important to check all samples under
ultra&iolet light regardless o% ,hether oil is suspected. Specimens ,ith mineral %luorescence should be labeled and set aside %or later
re%erence and comparison ,ith oil stained samples.
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The On-line Mud Logging Handbook Alun Whittaker
Petroleum Product #luorescence
Mud Additi&es
Some mud additi&es may also e-hibit traces o% %luorescence. / hope you took my ad&ice in Chapter .$ and remembered to keep samples o%
all mud additi&es( dry( ,ater and oil ,etA These should no, be close to hand( ,hile you are inspecting cuttings under the microscope( in
natural and ultra&iolet light. With these a&ailable %or re%erence( %e, mistakes should occur.
Oil-base * Additi&es
Oil and oil-based mud additi&es can be more o% a problem. Mineral oil and clean diesel oil ha&e no %luorescence or( at ,orst( a dull( dark
bro,n %luorescence. 3ombining this obser&ation ,ith a genuine hydrocarbon gas sho, that goes along ,ith oil additions see #lug Gas in
Chapter 6$ should allo, easy recognition.
?n%ortunately( the mutual solubility o% oils can complicate the situation. #ormation crude oil components ,ill dissol&e into oil-based additi&es
and oil-based muds adding their brighter %luorescence. ?nlike dissol&ed gas( these oils do not gradually e&aporate %rom the mud. The e-tra
%luorescent component ,ill be carried in the mud throughout the ,ell. '&en ,orse( ,ith a re-used( e-pensi&e oil-based muds( the
%luorescence may be carried %rom ,ell to ,ell( adding %luorescence color and intensity each time an oil-bearing Bone is penetrated.
When a routine sample is caught( the mud and un,ashed cuttings should be brie%ly inspected under ultra-&iolet light. This ,ill allo, you to
recogniBe the background %luorescence and( hope%ully( to pre&ent a later %alse alarm. Ho,e&er( you must remember that it is not the oil-
based mud that is %luorescing( but the true crude oil components carried in it. '&en the best mud logging techni1ue has its limits. /t may be
impossible to determine the nature o% a ne,ly penetrated potential reser&oir i% the mud already contains amounts o% similar oil and gas %rom
pre&iously drilled inter&als. '&en comparati&e techni1ues may not ,ork i% the mud contains a broad spectrum o% compounds %rom a range o%
pre&ious reser&oirs see Figures + and ,$. The true %ormation oil and gas sho, can be s,amped ,ith other oils and gases.
Pipe Dope
A %inal source o% %luorescence contamination is pipe dope( the hea&y( metaliBed grease used to lubricate and seal the threaded tool-0oints o%
drill pipe and drill collars2
✔ Pipe dope has a &ery bright gold( ,hite or blueish-,hite %luorescence apparently indicati&e o% the lightest( highest gra&ity oils or
condensate.
✔ #ortunately( such oils( in natural light are usually transparent( gold in color and readily e&aporate under the heat o% the illuminator.
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The On-line Mud Logging Handbook Alun Whittaker
✔ The hea&y( &iscous appearance and blue-black( or bro,n metallic color o% pipe dope in natural light are ob&ious con%irmation o% the
true nature o% this sho,.
Samples o% pipe dope( like anything else likely to %ind its ,ay into the mud( should be kept in the mud logging unit( dry( and in mi-tures ,ith
,ater and oil. Me sure to get samples o% all types2 o%ten the connections o% drill pipe( drill collars( casing collars( and other drill-string
components re1uire di%%erent types o% pipe dope or !P '-treme Pressure$ greases.
Mistakes can be made( but they can be minimiBed i% an e&aluation is made based upon all data a&ailable in the mud logging unit.
3onsider a reser&oir containing hea&y( lo, gra&ity( crude oil2
✔ The oil is dense( dark bro,n in color and has a lo, intensity( dark red-bro,n %luorescence actually( it ,ill ha&e bright in%ra-red-to-red
%luorescence but most o% this is not in the &isible range$.
✔ The addition o% pipe dope contamination to the cuttings %rom this %ormation may be disastrous. A little more hea&y( bro,n material
may be seen in natural light( but the pipe dopeDs bright ,hite %luorescence ,ill mask the real crude oilDs duller colors.
✔ Mased on &isual inspection( the Bone may be passed o&er( dismissed as a %alse alarm( but...
✔ /% this is a true oil reser&oir( then the oil ,ill contain some dissol&ed gas( including the hea&ier alkanes( propane( butanes and so on.
✔ Drilling the Bone ,ill produce a gas sho, o% increased magnitude and increased richness. This ,ould not be e-pected %rom a small
slick o% pipe dope.
✔ The increased porosity in the Bone may also be re%lected in drilling break N also not to be e-pected %rom man-made additi&es.
These indicators should 0usti%y care%ul( systematic sample e&aluation and lead you to a correct and complete e&aluation.
Sol&ent 3ut Test
Oil solubility is not al,ays a dra,back in reser&oir e&aluation. The sol&ent cut test is a use%ul companion to the cuttings blender test in
determining oil mobility( a combination o% the e%%ects o% oil &iscosity( gas-oil ratio and permeability. /t is also an aid in e-tracting the oil %rom
the cuttings and gi&ing a clear &ie,( remo&ed %rom the colored mineral background.
Se&eral di%%erent sol&ents are used %or this test2
✔ 3hloro%orm( or Trichloro-methane
✔ 3arbon Tetrachloride( Tetrachloro-methane( or Perchloro-methane
✔ 'thylene Dichloride( Sym-dichloro-ethane( 5(:-Dichloro-ethane also kno,n as 7utch "il$
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The On-line Mud Logging Handbook Alun Whittaker
✔ Methylene 3hloride( Methylene Dichloride( or Dichloro-methane
✔ 5(5(5-Trichloro-ethane( Methyl 3hloro%orm( or 3hlorothene
✔ 5(5(:-Trichloro-ethane( Iinyl Trichloride( or Meta-trichloroethane
✔ Trichloro-ethylene( 'thylene Trichloride( Triclene( or T3'( and sometimes the slang names2 tri( or trike
Oou may also come across di%%erent trade names( blends and &ariants o% these. 'ach has slightly di%%erent sol&ent properties and all o% them
are( to some degree( to-ic. When ,orking ,ith sol&ents al,ays ,ork ,ith small 1uantities in a ,ell-&entilated area. Jeep containers closed(
do not smoke and( lea&e the ,ork area and care%ully ,ash your hands be%ore eating or drinking anything. Dispose o% used sol&ents care%ully(
%ollo,ing all re1uirements pro&ided by the manu%acturer( the rig sa%ety rules( and the en&ironmental la,s o% the region in ,hich you are
,orking.
These are organic sol&ents and that includes youL
/n the sol&ent cut test( selected rinsed cuttings are placed in the depressions o% a ,hite porcelain spot plate( and a sol&ent is added.
Obser&ing the cuttings in natural and ultra&iolet light( ,ith the naked eye and under the microscope( the %ollo,ing characteristics can be
obser&ed2
3ut Speed
Solution o% oil in the sol&ent can take place instantly( rapidly( slo,ly( or not at all. This is an indication o% both the solubility o% the oil and the
permeability o% the cutting N the ease ,ith ,hich sol&ent can %lo, into the pore space( dissol&e the oil( and carry it out o% the cutting.
!eport you obser&ations o% cut speed as seen in both natural light and the color o% the cut$( and ultra&iolet light and %luorescent color$.
3ut <ature
3oloration o% the sol&ent ,ith dissol&ed oil may occur in a uni%orm manner( or ,ith streams o% color spreading une&enly out %rom the cutting.
A streaming cut also indicates lo, oil mobility( either due to unconnected pores( or a discontinuous or immo&able$ oil phase.
3ut 3olors
The color o% the oil dissol&ed in the sol&ent is obser&ed in natural light( and ultra&iolet light. A%ter solution( the sol&ent rapidly e&aporates
under the heat o% the illuminator lea&ing a residue o% oil around the cutting on the spot plate see Figure 6$. The true color o% the oil can then
be obser&ed.
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The On-line Mud Logging Handbook Alun Whittaker
#igure =2 #luorescence and cut testing %or oil must be per%ormed in a rigorous and systematic manner in order to a&oid
erroneous interpretations( missed sho,s or %alse alarms.
<atural and %luorescent colors may be seen more reliably ,hen the oil is remo&ed %rom the background color or %luorescence o% the cutting
onto the clean ,hite porcelain sur%ace o% the cut dish.
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The intensity and opacity o% color( especially o% the residue a%ter the sol&ent has e&aporated( is an indicator o% the oil density and o% the
1uantity o% oil originally contained in the cutting
!emember( that oil-based muds( additi&es and pipe dope
all dissol&e in the sol&ent and add natural or %luorescent
coloration to it. There is yet another source o% %luorescent
contamination2 the sol&ent itsel%L Although bulk supplies o%
sol&ent are commonly stored in metal or glass containers(
it is 1uite common %or the unitDs laboratory bench top
supply to be kept in a small plastic s1ueeBe or dropping
bottle.
<o, these bottles( and the material o% ,hich they are molded( are commonly described as being inert and non-%luorescent. This is probably
true %or most applications and short periods. Ho,e&er( / ha&e regularly obser&ed that( a%ter a %e, ,eeks o% use( both the bottle and its
contained sol&ent ,ill adopt a lo, le&el o% pale yello,-,hite %luorescence. This is not enough to cause a %alse oil sho, but enough to modi%y
the appearance o% a genuine oil sho,.
✔ /n the logging unit( bulk containers %or organic sol&ent should be made o% glass or metal and clearly labeled as being2
✔ F"R ")L &!#&# or
✔ F"R 7!-GR!A#)(G P8RP"#!# "(L9
✔ At the beginning o% each ,ell( the bench top dropping-bottle must be thro,n out and replaced.
✔ Once each ,eek the bench top container should be emptied into the de-greasing %luid container and re%illed %rom the clean sol&ent
supply.
✔ Me%ore per%orming the cut test( the sol&ent and its bottle should %irst be checked under ultra&iolet light %or %luorescence.
One %inal reminder2 ne&er use a plastic spot plate %or a sol&ent cut test or any kind o% oil e&aluation. / donDt care ,hat the guarantee says.
✔ /t may dissol&e in the sol&ent.
✔ /t may %luoresce.
✔ /t may become permanently stained and discolored.
✔ DonDt risk it.
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Th!s !s assm!ng the md logger !s s!ng laboratory +al!ty, porcela!n, spot Th!s !s assm!ng the md logger !s s!ng laboratory +al!ty, porcela!n, spot
plates ' not cheap plast!c ones, plates ' not cheap plast!c ones,
And the md logg!ng n!t has a plent!"l spply o" spot plates on hand ' And the md logg!ng n!t has a plent!"l spply o" spot plates on hand '
enogh so that every test can be per"ormed on a "resh, clean spot plate( %pot enogh so that every test can be per"ormed on a "resh, clean spot plate( %pot
plates shold be r!gorosly cleaned bet#een ses to remove all sta!n!ng and any plates shold be r!gorosly cleaned bet#een ses to remove all sta!n!ng and any
remnants o" "lorescence, and they shold be replaced #hen they start to remnants o" "lorescence, and they shold be replaced #hen they start to
become d!scolored( become d!scolored(
The On-line Mud Logging Handbook Alun Whittaker
Sample '-amination Procedure
The %irst sign o% a entry into a potential oil reser&oir is commonly a drilling break. This is an increase in rate o% penetration in response to the
lo, strength o% a porous %ormation.
/% the mud logger has a drilling data ac1uisition system see Chapter 1$( or i% a cooperati&e driller is a&ailable( he may also become a,are
that the rotary tor1ue has increased( and become more irregular. This might suggest a ,orn bit ,ith damaged bearings but( hope%ully( in this
instance it is responding to inhomogeneities in a granular or %ractured %ormation2 another indication o% good porosity.
On e-plorations ,ells( the drilling program ,ill o%ten dictate that( a%ter t,o or %i&e meters o% such beha&ior( drilling should be halted( and
circulation continued until samples are reco&ered and e&aluated. This is called circulating ottoms up.
Whether circulating or drilling ahead( the mud loggers should no, be getting ready %or their most hectic ,ork period. The laboratory area
should be cleaned up. Sample containers( sample e-amination tools( chemicals and re%erence materials laid out. The mud log is brought up
to date and then put a,ay.
For a 'hile0 there 'ill e time %or sample evaluation only: We hope;
A%ter the lag time has gone by( the %irst gas sho,s %rom the %ormation ,ill arri&e and an increase o% total hydrocarbons con%irms that a
hydrocarbon Bone has been penetrated.
✔ The proportions o% the alkanes in the chromatogram ,ill be a clue to the nature
o% %ormation hydrocarbons2 gas or oil. /% there is little or no change( then the
drilling break may indicate a ,ater-bearing Bone( or 0ust a lithological change.
✔ Samples o% ,ell cuttings must be caught in order to e&aluate the reser&oir
lithology( porosity( permeability and %luid saturations.
✔ #rom a time( ten minutes be%ore the e-pected %irst arri&al o% cuttings %rom the
%ormation( until uni%orm sample characteristics are established( samples o% mud
and cuttings %or e&aluation should caught at the smallest possible inter&al.
✔ /% it is not possible to complete all o% the tests and procedures %or each sample
at this rate( then portions o% mud( un,ashed or rinsed samples should be
labeled( sealed i% necessary( and set aside %or e&aluation later.
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A #ater-bear!ng reservo!r 7one re+!res as A #ater-bear!ng reservo!r 7one re+!res as
!ntens!ve sampl!ng and evalat!on as an o!l, or gas !ntens!ve sampl!ng and evalat!on as an o!l, or gas
"!lled one( 8n th!s #ell, #e may have penetrated "!lled one( 8n th!s #ell, #e may have penetrated
the reservo!r belo# the o!l-#ater contact( the reservo!r belo# the o!l-#ater contact(
Evalat!on o" the 7one can st!ll tell s a great deal Evalat!on o" the 7one can st!ll tell s a great deal
abot !t’s poros!ty, permeab!l!ty and reservo!r abot !t’s poros!ty, permeab!l!ty and reservo!r
potent!al( Evalat!on o" remnant traces o" o!l, may potent!al( Evalat!on o" remnant traces o" o!l, may
tell s someth!ng abot the o!l sorce, matr!ty tell s someth!ng abot the o!l sorce, matr!ty
and m!grat!on h!story( All o" th!s !s needed to plan and m!grat!on h!story( All o" th!s !s needed to plan
the ne&t #ell( the ne&t #ell(
The On-line Mud Logging Handbook Alun Whittaker
#igure 92 '&aluation o% mud and cuttings %or signs o% oil or residuum should be per%ormed routinely( Appro-imately once
each hour in all %ormations. /n potential or actual reser&oir rocks( the smallest possible sample inter&al should be used.
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The On-line Mud Logging Handbook Alun Whittaker
Mud Oil Sho, Tests
The mud sample is di&ided into %our portions see Figure .<=
✔ Portion -* is immediately poured into a shallo, dish and placed under the ultra&iolet light to obser&e sign o% %luorescence in the mud
itsel% or droplets o% immiscible( light oil popping to the sur%ace o% the denser mud.
/% at %irst( nothing is seen( the sample a le%t to stand and obser&ed periodically o&er se&eral minutes.
✔ Portion -+ is mi-ed ,ith an e1ual 1uantity o% ,ater to decrease its &iscosity( stirred and then treated in the same manner as Portion
-*.
✔ Portion -, is used %or the mud blender gas analysis.
A%ter analysis( li%t the blender gas care%ully and check %or a petroleum odor.
✔ 3ontrary to a common misconception( light alkane gases ha&e no detectable odor.
✔ Oil-like odors are a de%inite indication o% the presence o% oil.
✔ Touch the sur%ace o% the ,ater ,ith a dry %ilter paper.
✔ This ,ill pick up any oil droplets ,hich may then be seen under ultra&iolet light.
✔ A%ter these tests( proceed to the normal sample processing procedure as discussed in Chapter ..
✔ Portion -5 is %iltered ,ith the mud %ilter press and a coarse grade o% %ilter paper this does not yield a &alid ,ater loss measurement
but produces a rapid sample o% mud %iltrate$.
✔ The salinity is determined ,ith a electrical resisti&ity meter( or sil&er nitrate titration.
✔ A pH meter( pH test paper or titration is used to determine the acidity pH$.
3hanges in mud salinity ,ithin the reser&oir may indicate a high ,ater saturation or e&en identi%y the oil ,ater contact. Decrease in
mud pH may indicate the presence o% sour gas N 3arbon Dio-ide or Hydrogen Sul%ide N in the reser&oir.
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?n,ashed 3uttings Oil Sho, Tests
The sample o% un,ashed cuttings is treated in the normal manner see Chapter .$ e-cept that t,o small portions are taken aside and
checked %or %luorescence in the same manner as the %irst t,o drilling mud samples aove$2
✔ Portion -* is immediately poured into a shallo, dish and placed under the ultra&iolet light to obser&e sign o% %luorescence in the mud
itsel% or droplets o% immiscible( light oil popping to the sur%ace o% the denser mud coating the cuttings.
/% at %irst( nothing is seen( the sample a le%t to stand and obser&ed periodically o&er se&eral minutes.
✔ Portion -+ is mi-ed ,ith an e1ual 1uantity o% ,ater to decrease its &iscosity o% the mud coating( thoroughly mi-ed and then treated in
the same manner as Portion -*.
A%ter the cuttings blender test( the 0ar and ,ater are inspected %or oil signs 0ust like the mud blender test aove$.
A%ter routine cuttings sample processing see Chapter .$( the lithology e&aluation sample is di&ided into t,o more portions -, and -5$.
'ach consists o% a representati&e sample o% cuttings( spread thinly on a sample tray see Figure .$.
✔ Portion -, is placed under the microscope and e-amined in the normal manner %or lithological e&aluation.
An estimate is made o% the proportion o% apparently oil stained material( and &isible oil staining is described2
✔ Appearance2 oily( ,a-y( dry residue
✔ Distribution2 e&en( spotty( patchy( streaks
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Th!s probably belongs, not here, bt !n a sample e&am!nat!on manal bt I #ant to br!ng !t p( .ar too o"ten, md loggers Th!s probably belongs, not here, bt !n a sample e&am!nat!on manal bt I #ant to br!ng !t p( .ar too o"ten, md loggers
and geolog!sts p!le ctt!ngs !nto a sample tray, a hal" cent!meter or more deep( Th!s may be a good #ay to load a dry!ng tray and geolog!sts p!le ctt!ngs !nto a sample tray, a hal" cent!meter or more deep( Th!s may be a good #ay to load a dry!ng tray
"or ma)!ng #ashed-and-dr!ed sample( It !s no #ay to per"orm geolog!cal, or o!l evalat!on( "or ma)!ng #ashed-and-dr!ed sample( It !s no #ay to per"orm geolog!cal, or o!l evalat!on(
9nder the m!croscope, th!s tray o" ctt!ngs #!ll present an !rreglar top sr"ace, part above and part belo# o" the range o" 9nder the m!croscope, th!s tray o" ctt!ngs #!ll present an !rreglar top sr"ace, part above and part belo# o" the range o"
"ocs( *hen yo try to man!plate or p!c) p a ctt!ng #!th a probe or t#ee7ers, most l!)ely yo #!ll psh !t do#n !nto the "ocs( *hen yo try to man!plate or p!c) p a ctt!ng #!th a probe or t#ee7ers, most l!)ely yo #!ll psh !t do#n !nto the
mass o" other ctt!ngs and ot o" "ocs( Ctt!ngs shold spread across the sr"ace o" a clean sample tray or "!lter paper, no mass o" other ctt!ngs and ot o" "ocs( Ctt!ngs shold spread across the sr"ace o" a clean sample tray or "!lter paper, no
more than one ctt!ng deep( more than one ctt!ng deep(
The On-line Mud Logging Handbook Alun Whittaker
✔ Hue and intensity o% color on ,et and dry cuttings.
Take a representati&e number o% apparently oil stained cutting %rom the sample tray and place them in the depressions o% a ,hite
porcelain spot plate( ,ith no more than one cutting in each depression. Add sol&ent to hal% o% the depressions on the spot plate to
per%orm a cut test. Sol&ent cut is described2
✔ !ate(
✔ <ature(
✔ 3olor and intensity o% sol&ent cut and oil residue a%ter e&aporation$.
✔ Portion -5 is inspected under ultra&iolet light. An estimate is made o% the proportion o% %luorescent cuttings and %luorescence is
described2
✔ Distribution2 e&en( spotty( patchy( streaks$(
✔ Hue and intensity o% color %luorescence.
Take a representati&e number o% %luorescent cuttings %rom the sample tray and place them in the depressions o% a second spot plate.
Add sol&ent to hal% o% the depressions on the spot plate to per%orm another cut test. Sol&ent cut is described2
✔ !ate(
✔ <ature(
✔ 3olor and intensity o% %luorescence.
Oou ha&e no, positi&ely identi%ied and placed on spot plates2
✔ #pot Plate -*= 3uttings ,ith an oily appearance under ,hite light( and
✔ #pot Plate -+= 3uttings ,ith %luorescence under ultra&iolet light
✔ #pot Plate -,= 3uttings that ,ith a sol&ent cut &isible under natural light.
✔ #pot Plate -5= 3uttings that ,ith a sol&ent cut &isible under ultra&iolet light.
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<e-t( s,ap the spot plates( so that2
✔ The cuttings described as oil stained can be e&aluated %or %luorescence and cut.
✔ The %luorescent cuttings can be e&aluated %or &isible oil staining and cut.
✔ The color and beha&ior o% the cut can be obser&ed in natural light( ultra&iolet light( and under the microscope.
My per%orming this doule lind test you can be certain that the cuttings contained a true( %luorescent oil stain( ,a-( or tar residue. Oou
ha&e eliminated the risk o% %alse alarms such as seeing non-%luorescent$ diesel oil stain on some cuttings( and %alsely matching this ,ith
mineral %luorescence on others( and a pipe dope cut on yet others.
/ ha&e regularly seen mud loggers and ,ell-site geologists take spoons-%ul o% cuttings in a dish( add sol&ent( s,irl and look at them under
ultra&iolet light. This can make a 1uite impressi&e light sho,( but it is 0ust a sho,. /t is also a ,aste o% &aluable time and &aluable sample. /%
the sample sho,s all possible signs o% being oil-bearing but has no sol&ent cut( it may be ,orth trying to %orce a cut by crushing the sample(
adding a little dilute acid( hot ,ater( or trying the test on a ,arm( rinsed and dried sample.
This sometimes ,orks on carbonates ,ith e-tremely lo, e%%ecti&e porosity and permeability could be impro&ed in producing ,ells by %racture
or acid stimulation. /% the cut test is success%ul under these conditions then describe the results in the normal ,ay. O% course( ,hen reporting
the results on the log or core report( the added steps needed to induce the sol&ent cut should be e-plained.
Automated #luorimetry
Oil %luorescence e&aluation is a simple( reliable method o% locating and characteriBing oils. ?n%ortunately( ,hen many di%%erent %luorescent
compounds are already present the mud( the addition o% small amounts o% one ne, component may be missed. #luorimetry upgrades
%luorescence analysis ,ith automation and an e-tra dimension o% measurement.
Oou ,ill remember that( a%ter e-citation( a %luorescent compound may emit radiation at one or more characteristic longer ,a&elength. Thus( it
should be possible to characteriBe %luorescence by both the ,a&elength or color$( and the intensity or brightness$( o% the emitted light.
/% our ultra&iolet inspection system used a photocell instead o% our eyes then( it ,ould be possible to measure the intensity o% %luorescence
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I" yo don’t remember, please go bac) to the I" yo don’t remember, please go bac) to the beginning beginning , and I’ll #a!t "or yo here((( , and I’ll #a!t "or yo here(((
((( as I )eep tell!ng yo, once yo get the bas!cs (no matter ho# !rrelevant they may seem at the ((( as I )eep tell!ng yo, once yo get the bas!cs (no matter ho# !rrelevant they may seem at the
t!me), yo #!ll be able to "!gre ot any ne# s!tat!on or technology that yo meet p #!th later( t!me), yo #!ll be able to "!gre ot any ne# s!tat!on or technology that yo meet p #!th later(
The On-line Mud Logging Handbook Alun Whittaker
and detect an increase in intensity ,hen a oil-bearing Bone is %irst encountered see Figure 2$.
#igure >2 Euantitati&e #luorescence intensity impro&es correlation o% sho, 1uality bet,een Bones. On a computer-
generated mud log( both intensity( and color-coded appro-imation o% %luorescent color helps illustrate both the oil sho,
1uality and type.
/n order to impro&e reproducibility( t,o additional steps are re1uired2
✔ 'stablishing a baseline intensity the %luorescence intensity o% mud %iltrate( cuttings minerals( and contaminants prior to addition o% the
oil stain to be e&aluated$( and
✔ Preparing a standard siBed( and standardly processed sample.
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Oil #luorescence can be %urther automated using scanning spectroscopy see La'0 *12*( and Figure 1$. ?sing a spectrometer( a sample o%
%lo,-line mud or un,ashed -- easier to standardiBe than selecting %rom ,ashed cuttings$ is e-cited at a range o% e-citation ,a&elengths(
and the intensity o% emission %luorescence can be measured at each o% its separate e-citation ,a&elengths.
#igure 42 A %luoro-spectrometer can detect 1uantitati&e %luorescence at a range o% e-citation ,a&e lengths
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The +est!on ar!ses -- are #e plann!ng to measre the !ntens!ty o" "lorescence "rom a standard volme o": The +est!on ar!ses -- are #e plann!ng to measre the !ntens!ty o" "lorescence "rom a standard volme o":
Ctt!ngs selected at random Ctt!ngs selected at random
%elected "lorescent ctt!ngs %elected "lorescent ctt!ngs
%elected (apparently) o!l-sta!ned ctt!ngs %elected (apparently) o!l-sta!ned ctt!ngs
A comb!nat!on o" the second and th!rd opt!ons (o!l-sta!ned A4D "lorescent) #old be more val!d and reprodc!ble, bt !t #old A comb!nat!on o" the second and th!rd opt!ons (o!l-sta!ned A4D "lorescent) #old be more val!d and reprodc!ble, bt !t #old
!t re+!re +!te an e""ort !n ctt!ngs p!c)!ng to prodce a large enogh sample "or measrement( !t re+!re +!te an e""ort !n ctt!ngs p!c)!ng to prodce a large enogh sample "or measrement(
The On-line Mud Logging Handbook Alun Whittaker
Oil-based components and contamination in the drilling %luid may contain some similar or related hydrocarbons to those in the reser&oir
crude oil. Other components ,ill be uni1ue to each o% them. O%ten( those uni1ue components ,ill respond to di%%erent e-citation ,a&elengths
and emit at di%%erent emission ,a&elengths. A spectrogram o% emission %luorescence intensity o&er a range o% e-citation ,a&elengths sho,s
di%%erences in %luorescence intensity bet,een an oil sho, sample and the established background. Subtracting the base-oil signature it is
possible to recogniBe the presence and relati&e amount o% a genuine ne, oil sho, see Figure *>$.
#igure 562 Euantitati&e %luorescence using a scanning spectrometric
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#or e-ample( in Figure *>( you can see that2
✔ At the e-citation ,a&elengths labeled A( emission %luorescence is present in both background and oil sho, samples ,ith a similar
intensity. Ob&iously( the components e-cited at these ,a&elengths are present in similar amounts in both. They are most likely
components o% the drilling %luid or contamination %rom pre&iously drilled Bones.
✔ At the e-citation ,a&elength labeled ?( emission %luorescence is present in both background and oil sho, samples( but there is
greater intensity in the oil sho, sample. The components e-cited at this ,a&elength are likely present in both samples( but more has
been added to the oil sho, sample. These components are most likely %ormation hydrocarbons( ,ith trace amounts carried as
contaminants in the background sample( ,ith increased amounts added %rom the drilled reser&oir being seen in the oil sho, sample.
✔ At the e-citation ,a&elengths labeled C( emission %luorescence is present in only the oil sho, sample. The components e-cited at
this ,a&elength are most likely uni1ue components o% %ormation hydrocarbons( not seen be%ore( and introduced by drilled cuttings
contributing to the oil sho, sample.
?sing ,ater-based muds( the base-line or background$ &alues o% %luorescence can be reliably obtained %rom circulating %luids( stabiliBed by
one or t,o %ull circulations much like establishing the circulating background %or total hydrocaron gas detection$.
Ho,e&er( it has been %ound( ,hen using oil-based mud( that a base-line or background$ &alue o% %luorescence intensity can only be reliably
achie&ed by continuous sampling the mud as it enters and e-its the hole. Jno,ing the do,n-time and lag time it is possible to determine a
continuous di%%erential intensity. This is the increase in %luorescence intensity as the mud passes through the bore hole( and carries the
cuttings %rom each ne,ly drilled inter&al.
Sample standardiBation and a reduction in the necessary sample processing e%%ort$ can be achie&ed by taking a %i-ed &olume o% mud or
un,ashed cuttings and agitating it ,ith an e1ual &olume o% a clean organic sol&ent such as He-ane. This can be done by hand but e&en
better standardiBation is achie&ed ,ith mechanical grinding and agitation.
The method is a contribution to %ormation e&aluation but in oil-based muds( and ,hen drilling e-tensi&e or multiple pay Bones( the o&erall
intensity and &ariability o% the background may be so great that smaller &ariations due to changes in %ormation hydrocarbons may be di%%icult
to isolate.
Another possible impro&ement through automation in&ol&es per%orming synchronous scan %luorescence spectrometry see ?ather0 *125 (
and Connell0 Coates0 4 Frost0 *126$. /n this method( the e-citation ,a&elength is progressi&ely changed and a series o% %luorescence
emission spectra are generated. When stacked together( these can be used to create a three-dimensional spectrogram see Figure **$ in
,hich %luorescence intensity peaks are de%ined by e-citation ,a&elength and emission ,a&elength.
Fust as in single scanning spectroscopy( it is possible to recogniBe the presence and relati&e amount o% a genuine ne, oil sho, %rom the
location and height either in a ,-7 graphic display or( in t,o dimensions( as a contour plot$ o% peaks. ?n%ortunately( e&en ,ith synchronous
scanning spectroscopy( practical e-perience has %ailed to achie&e complete reliability ,hen %aced ,ith the problem o% contamination %rom
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saturated( oil-based mud. O%ten the mud( contaminated ,ith oil %rom many di%%erent sources( produces such intense %luorescence %rom so
many ,a&elengths that it s,amps the entire %luorescence spectrum and pre&ents any uni1ue peak %rom being recogniBed.
#igure 552 Euantitati&e %luorescence using a synchronous scanning spectrometry plotted as t,o-dimensional contour
plot. <ote that the colors used represent( gradations o% %luorescent intensity( and not %luorescence color as sho,n in
Figure 2$. When setting up a computer plotter to create a contour plot o% this this type( you should take care to select
colors or te-tures %rom the de&ice@s palette that cannot be misunderstood.
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#luorescence spectrometry has a great potential as a ,ell-site analytical tool and it could become an ideal complement to chromatography.
Some recent ,ork by Te-aco no, 3he&ron-Te-aco$ has made an important contribution by de&eloping a systematiBed methodology %or
sample processing( analysis( and data presentation see 7elaune0 *11+$ and 7elaune0 #pilker0 4 Wright0 *111$ . These methodologies
ha&e been patented under the names Euantitati&e #luorescence Techni1ue @F&
&M
and @F&+
&M
$.
✔ The original process( called @F&( pro&ides a plot o% %luorescence intensity against depth( similar to that illustrated in Figure 2. ?sing
an empirical calibration against a large database o% samples %rom oil producing inter&als( the E#T method attempts to determine a
1uantitati&e oil concentration %unction.
✔ @F&+ see 7ick0 +>>/$ e-tends the basic process using t,o simultaneous e-citation ,a&elengths( a computer program to calculate
the ratio o% the emission %luorescence intensities see Figure *+$. #rom that( it is also claimed that it is also possible to compute
empirical estimates o% oil percentage by ,eight$( oil density as AP/ )ra&ity$( and the &olume o% oil-%illed porosity.
#igure 5:2 Well-to-,ell correlation using a E#T %luorescence log
The Te-aco E#T( and the E#T: techni1ues ha&e been licensed and are no, o%%ered by a number o% mud logging contractors. As solid
state( analytical instruments becomes more rugged( more capable( and cheaper( ,e should e-pect to see more e%%orts along the lines
proposed by Te-aco.
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O% course( the methodology is entirely empirical( but i% your conclusions are to stand only upon an established record o% pre&ious results(
then probably those methods de&eloped by huge( international e-ploration companies ,ith the bene%it o% their huge( international
databases$ should be most ,orthy o% trust.
Euantitati&e %luorimetry does break mud
logging golden rule numer t'o( by
re1uiring a day rate instrument to be kept
and paid %or$ on site %or the ,hole ,ell( although it is to be used only %or short periods. On the other hand( it meets the appro&al o% golden
rule numer three0 in that it re1uires little specialiBed additional skill or time to run.
Any %luorescence measurement should be per%ormed on &ery %resh samples. Analysis at some later time and place is unlikely to be so
use%ul( nor so &aluable. '&en ,ith care%ully sealed samples( sample %luorescence ,ill be depleted and( a%ter the ,ell has been completed(
any real-time decisions to ,hich a mud logging measurement could ha&e contributed ,ill ha&e already been made( or ,ill be no longer
rele&antP better( alternati&e data no, being a&ailable.
'&en ,ithout the some,hat e-tra&agant claims made %or E#T( 1uantitati&e %luorimetry( particularly ,hen enhanced ,ith some element o%
spectroscopy as discussed abo&e( ,ill e&entually become an important tool in e&aluating di%%icult drilling problems and situations.
These include2
✔ Drilling ,ith oil-based drilling %luids(
✔ '&aluating multiple or repeated oil Bones( and
✔ 3orrelation and steering in boundary detection on horiBontally drilled ,ells.
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8 8bv!osly, the sccess o" the method as #!th others (see bv!osly, the sccess o" the method as #!th others (see Chapter 13 Chapter 13) can only be ) can only be
ma!nta!ned !" ne# data !s gathered to both re!n"orce the general model, and to develop and ma!nta!ned !" ne# data !s gathered to both re!n"orce the general model, and to develop and
re"!ne more prec!se reg!on-spec!"!c, or reservo!r-type-spec!"!c correlat!ons( re"!ne more prec!se reg!on-spec!"!c, or reservo!r-type-spec!"!c correlat!ons(
The On-line Mud Logging Handbook Alun Whittaker
!e%ractometry
?ntil %luorescence spectrometers ha&e been reduced enough to %it e&ery pocket N in both siBe and price N there is another 1uantitati&e
optical techni1ue that is already able to %it that speci%ication2 re%ractometry.
!e%ractometry( has been used %or many years in industrial petro-chemistry. Precise correlations has been de&eloped relating oil gra&ity and
re%racti&e inde- %or &arious oil base types and re%ined products. Where the base type o% a crude oil is unkno,n( a simple empirical(
generaliBed relationship can be used ,ith acceptable accuracy see Figure *5$. /n the past( re%ractometers ha&e rarely been used at the
,ell site because o% the high price and delicacy o% the traditional AbbQ re%ractometer.
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It !s n"ortnate that the !ntrodct!on o" any ne# or enhanced md logg!ng serv!ce !s, more o"ten than not, accompan!ed by overblo#n It !s n"ortnate that the !ntrodct!on o" any ne# or enhanced md logg!ng serv!ce !s, more o"ten than not, accompan!ed by overblo#n
cla!ms( It never seems to be enogh to demonstrate an !mprovement !n the real t!me md log data( Cla!ms to prov!de data comparable cla!ms( It never seems to be enogh to demonstrate an !mprovement !n the real t!me md log data( Cla!ms to prov!de data comparable
#!th, or better than that "rom #!re-l!ne logs, core analys!s, or #ell tests al#ays seem to be p!led on( #!th, or better than that "rom #!re-l!ne logs, core analys!s, or #ell tests al#ays seem to be p!led on(
In my op!n!on, th!s over-cla!m!ng !s st!mlated by the md logg!ng contractors "a!lre to sell (and the!r cstomers to apprec!ate) the real- In my op!n!on, th!s over-cla!m!ng !s st!mlated by the md logg!ng contractors "a!lre to sell (and the!r cstomers to apprec!ate) the real-
t!me !mportance o" md log data (see t!me !mportance o" md log data (see Chapter 1 Chapter 1)( Instead o" mar)et!ng t!mely data, that allo#s !mproved and accelerated real-t!me )( Instead o" mar)et!ng t!mely data, that allo#s !mproved and accelerated real-t!me
dec!s!on ma)!ng, the md logg!ng contractors try to prom!se data o" a +al!ty srpass!ng that ava!lable later "rom other serv!ces( %!nce dec!s!on ma)!ng, the md logg!ng contractors try to prom!se data o" a +al!ty srpass!ng that ava!lable later "rom other serv!ces( %!nce
these other serv!ces #!ll cont!ne to be rot!nely per"ormed, and so these over-amb!t!os cla!ms cannot o""er any cost bene"!t( 4o matter these other serv!ces #!ll cont!ne to be rot!nely per"ormed, and so these over-amb!t!os cla!ms cannot o""er any cost bene"!t( 4o matter
#hat the salesman has to o""er, !t !s ld!cros to e&pect the some ne# md logg!ng techn!+e #!ll reslt !n rnn!ng less #!re-l!ne logs, #hat the salesman has to o""er, !t !s ld!cros to e&pect the some ne# md logg!ng techn!+e #!ll reslt !n rnn!ng less #!re-l!ne logs,
ctt!ng less cores, or test!ng "e#er !ntervals( The e&plorat!on!st cares abot hav!ng the most data at the end o" the #ell, no matter ho# or ctt!ng less cores, or test!ng "e#er !ntervals( The e&plorat!on!st cares abot hav!ng the most data at the end o" the #ell, no matter ho# or
#hen !t #as gathered( #hen !t #as gathered(
Dr!ll!ng "oremen and eng!neers, on the other hand, are !n the bs!ness o" ;ma)!n2 hole<( They #ant all the !n"ormat!on then can get, as Dr!ll!ng "oremen and eng!neers, on the other hand, are !n the bs!ness o" ;ma)!n2 hole<( They #ant all the !n"ormat!on then can get, as
soon as they can get !t( It !s srpr!s!ng that #hen, dr!ng the soon as they can get !t( It !s srpr!s!ng that #hen, dr!ng the =>s and ?>s, there #as ma,or gro#th !n the cost and comple&!ty o" md =>s and ?>s, there #as ma,or gro#th !n the cost and comple&!ty o" md
logg!ng serv!ces, !t mostly came "rom the add!t!on o" dr!ll!ng data ac+!s!t!on, opt!m!7at!on, and pressre evalat!on serv!ces( Commonly logg!ng serv!ces, !t mostly came "rom the add!t!on o" dr!ll!ng data ac+!s!t!on, opt!m!7at!on, and pressre evalat!on serv!ces( Commonly
!t seemed that the Dr!ll!ng Department #as better e+!pped than the E&plorat!on Department to ma)e se o" real-t!me data, both !n !t seemed that the Dr!ll!ng Department #as better e+!pped than the E&plorat!on Department to ma)e se o" real-t!me data, both !n
t!me saved, and !n dec!s!ons made sooner #h!ch, "or them, also meant better( t!me saved, and !n dec!s!ons made sooner #h!ch, "or them, also meant better(

The On-line Mud Logging Handbook Alun Whittaker
#igure 5;2 This Atago hand re%ractometer is made in Fapan and is not surprisingly$ compact( reliable and reasonably
priced. <eed / say moreA This particular one / donated to the Stan%ord ?ni&ersity Petroleum 'ngineering Department
OJ( it@s not a ,hole building( but then /@m not Mill )atesL$
A portable re%ractometer( similar to the Atago de&ice sho,n in Figure *,( pro&ides a simple( speedy alternati&e %or measuring re%racti&e
inde-. An added ad&antage o% the techni1ue is that it re1uires only a small &olume o% oil. A sample o% ,ell cuttings can pro&ide su%%icient oil
to co&er the small optical cell in the re%ractometer see Ainghorn0 *12,$. Alternati&ely( you can use the smear o% oil le%t behind in the cut
dish a%ter the sol&ent cut test( and be%ore complete e&aporation o% the sol&ent.
A hand re%ractometer is( ob&iously less accurate than the laboratory AbbQ re%ractometer but it is simpler( easier to operate and re1uires no
more sample than can be s1ueeBed %rom a %e, grams o% crushed cuttings. My using only cuttings samples( it is possible( ,ith minimal e%%ort
to a&oid the ,orst o% oil-mud contamination problems and detect any true crude oil( i% present( by its di%%erence in re%racti&e inde- and gra&ity
%rom that o% the re%ined oil-base and its contaminants.
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#igure 572 !e%ractometry ,as de&eloped %or use in petro-chemistry and %ood technology to determine oil purity %rom a
measurement o% !e%racti&e /nde-. This empirical relationship bet,een !e%racti&e /nde- and AP/ )ra&ity o% crude oil
gi&es reasonable accuracy e&en ,hen the oil base type is unkno,n.
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Well-site )eo-chemistry
Mud logging has al,ays been a kind o% ,ell-site geo-chemistry. /n recent years( impro&ed instrument construction technology has allo,ed
more types o% geo-chemistry to become part o% mud logging. More could %ollo, but( in practice there are limitations.
#irstly( the petroleum e-ploration industry de%ines geo-chemistry as the organic chemistry o% petroleum precursors N it is the science o% the
source bed( not o% the reser&oir. The chemistry o% petroleum itsel% is peripheralP minerals and pore ,aters are 1uite out o% the picture.
?sually( these %all ,ithin the realm o% the petro-chemists and petro-physicists respecti&ely. ThatDs okay( thereDs plenty o% problems to go
around.
<e-t( there are practical and cost limitations to per%orming geo-chemistry at the ,ell site. Much geo-chemical sample processing and
analysis e1uipment is large( delicate( e-pensi&e and slo,. /t does not lend itsel% to operation in real-time operations and to the cro,ded(
non-sterile conditions o% the mud logging unit. Much o% it cannot sur&i&e ,ithout skilled technicians to keep it in-tune( and analytical chemists
to %ollo, detailed sample preparation procedures. #inally( the data obtained %rom this kind o% oil%ield geo-chemistry is o%ten re1uired only
%rom limited sections o% the ,ell and mostly %or strategic( rather that real time decision making. The data may not be used until late in the
e-ploration or de&elopment program. /n most circumstances( it ,ould be ,aste%ully e-pensi&e to install this type o% e1uipment at the rig site
%or an entire ,ell( or e&ery ,ell.
On the other hand( the limitations o% remote and international operations %or comparison( see Core Analysis in Chapter .$ may make it
easier to ha&e the e1uipment a&ailable at or near the ,ell site( rather that to mo&e the samples to the e1uipment on another continent. This
does not necessarily mean that the geo-chemical analyBers are literally installed in the mud logging unit. On many large( o%%shore( arctic and
0ungle camp locations( comparati&ely %ully e1uipped geo-chemistry laboratories ha&e been installed( complete ,ith the most delicate
instrumentation and the specialiBed personnel to maintain it. Where this is not possible( some geo-chemical or mud logging contractors can
pro&ide a %ield geo-chemistry unit %or location at remote shore base( or operations centers.
These %ield geo-chemistry laboratories are sel%-contained and portable( like a mud logging unit( although !a%ael )ur&is( one o% the pioneers
o% %ield geo-chemistry( al,ays re%erred to them as not portale ut transportale see Gurvis0 Whittaker0 4 Aremuru0 *12+$. My this( he
meant that the portable buildings could be
mo&ed %rom place to place but that they
re1uired considerably more e%%ort in setting-
up( calibrating( and standardiBing o% the
e1uipment than a regular mud logging unit
,ould need.
An alternati&e to this are locally established laboratories o% ma0or geo-chemistry contractors( local companies and 0oint &entures. These are
o%ten better e1uipped though they may be less ,ell sta%%ed and standardiBed than the %ield laboratories operated by a ,ell organiBed multi-
national ser&ice company. #inally there are the laboratories operated by the ma0or geo-chemical ser&ice companies and by oil companies
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There may be trth !n th!s, bt !t al#ays broght !nto my m!nd an !mage o" a sl!c) salesman There may be trth !n th!s, bt !t al#ays broght !nto my m!nd an !mage o" a sl!c) salesman
#ho hyped h!s prodct by e&pla!n!ng that !t #as not a #ho hyped h!s prodct by e&pla!n!ng that !t #as not a por table por table hose tra!ler, bt a hose tra!ler, bt a
tr anspor table tr anspor table mob!le home( mob!le home(
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themsel&es in oil%ield centers( like the Los Angeles( London( Paris( San #rancisco( 3algary( Rhan0iang( Houston and so on. These are
ob&iously the ideal location %or analyses to be per%ormed( ,ith standardiBation o% procedures and personnel. ?n%ortunately( as ,eD&e seen( it
is not al,ays possible to get the samples to such a location in a time and condition acceptable %or analysis.
/n the %ollo,ing discussion( / ,ill limit mysel% to those analyses ,hich ha&e been o%%ered and pro&ided as ,ell-site ser&ices in mud logging
units on e-ploration ,ells. Oou must decide ,hich o% them %ul%ill the cost( practicality and timeliness parameters %or your o,n operation.
Again( ,ith impro&ed solid state components and processor po,er( this list ,ill continue to gro, and change( both by impro&ed and lo,-
priced instrumentation( and more producti&e utiliBation o% geo-chemical data ,hile drilling.
#igure 582 The L'3O
G
3!-5: Total Organic 3arbon TO3$ analyBer pro&ides the basic geo-chemical measurement
used to indicate source bed 1uality and against ,hich to normaliBe all other geo-chemical measurements. /llustration
courtesy o% 'HLO)( /nc.$
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Total Organic 3arbon
The earliest and( you ha&e my personal assurance( heaviest geo-chemical analyBer to make the mo&e %rom laboratory to ,ell site ,as the
Total Organic 3arbon TO3$ analyBer. There are many &ersions o% this but( in the oil%ield( the L'3O
G
3!-5: see Figure */$ is probably the
standard instrument.
Sample preparation %or TO3 analysis2is &ery time and labor intensi&e( so it is usual to process a large number o% samples and analyBe them
as a batch. /% the analysis is being per%ormed in a mud logging unit( this is best done during trips or other do,n time ,hen the mud logging
,ork load( and other unit acti&ity is reduced.
Sample preparation is as %ollo,s2
✔ Appro-imately :6 grams about S ounce$ o% sample must be selected %rom *.>-mesh sieved cuttings care%ully inspected %or
uni%ormity and the absence o% mud contaminants and organic debris( particularly rubber and plastic.
✔ The cuttings are air dried %or about t,o hours and then ground in a mortar and pestle( slo,ly and care%ully( to a&oid %rictional heating.
✔ A%ter grinding( hal% the sample is set aside %or re-testing and other analyses see belo,$.
✔ #rom the other hal% o% the sample( one gram o% sample is ,eighed and then digested ,ith ,arm( dilute 56T$ Hydrochloric acid until
all carbonate material has %ully reacted and 3arbon Dio-ide e&olution is complete see Waples0 *12/$.
✔ The sample is then re-,ashed( air dried at lo, temperature and care%ully trans%erred into an unglaBed ceramic crucible.
Analysis itsel% is much simpler and 1uicker than sample preparation.
✔ The sample is enclosed in a induction %urnace and s,ept ,ith a supply o% pure o-ygen.
✔ As temperature increases( complete combustion o% all remaining %ree carbon and carbon compounds in the sample produces 3arbon
Dio-ide ,hich is detected by a thermal conducti&ity detector T3D$.
✔ ?sing pre-mi-ed standards o% kno,n carbon content( the detector can be calibrated in terms o% percentage carbon content by ,eight.
With all carbonate material content remo&ed %rom the sample( the TO3 analyBer ,ill reliably indicate only the organic carbon content o% the
rock. TO3 is a use%ul basic geo-chemical tool in obtaining a 1uantitati&e estimate o% the organic-richness and the petroleum producing
capability o% clay or lime mudstone source beds. #igure 5= is a table illustrating the general relationship bet,een source bed 1uality and
TO3 %or shale and carbonate source beds.
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Total organi! !arbon per!entage :b-5eight;: 'our!e bed <ualit
Clastones = 'hales Carbonates
Less than ->1- Less than ->-1 ?nsignifi!ant
->1 to ->%, ->-1 to ->1- Poor
->%, to ->,- ->1- to ->%, 6air
->,- to 1>-- ->%, to ->,- Moderate
1>-- to %>-- ->,- to 1>-- $ood
$reater than %>-- $reater than 1>-- "@!ellent
#igure 5=2 Total Organic 3arbon content and source bed 1uality %or argillites claystones and shales$ and carbonate
rocks limestones( dolomites and calcareous mudstones$.
?n%ortunately( these &alues are not entirely decisi&e because Total Organic 3arbon alone is not capable o% discriminating bet,een2
✔ #resh organic debris(
✔ Jerogen o% &arious types( or diagenetic le&els(
✔ Hydrocarbon oils( tars( or
✔ 3oal( or metamorphic graphite
)ases and the lighter( more &olatile oils( o% course( are not a %actor( being lost %rom the sample during the grinding and air drying stages o%
preparation. So TO3 alone has little diagnostic &alue as a real-time tool operating at the ,ell site ,hile drilling. /n the laboratory( TO3 data is
combined ,ith other analyses so that the amount and type o% organic material can be determined. They are plotted together on a separate
geo-chemical log.
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At the ,ell site( in the absence o% other geo-chemical analyses( mud log hydrocarbon and lithology data may be added to TO3 data to
produce a ,ell-site source bed e&aluation log see Figure *.$.
#igure 592 Total Organic 3arbon pro&ides a reliable 1uantitati&e estimate o% the richness o% organically-deri&ed carbon.
?n%ortunately it cannot indicate the type or present diagenetic state o% the organic material ,ithout additional geo-
chemical or mud logging data.
?sing this combination o% data( TO3 becomes a use%ul part o% the mud log suite( enhancing %ormation e&aluation and impro&ing the
1ualitati&e and 1uantitati&e interpretation o% both source beds and reser&oirs. To put it another ,ay( e&en though the geo-chemical analyses
are being per%ormed %or other audiences and on other budgets( they still can be used to yield use%ul in%ormation %or the e-plorationists
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,orking at the ,ell site.
Pyro-analysis
/n the study o% hydrocarbon detection ,e ha&e looked at both normal and catalytic combustion. Despite occurring at di%%erent gas-air
compositions and rates( both o% these in&ol&e the thermal decomposition o% a hydrogen and carbon-containing compounds in air( and the
combination o% the products o% decomposition ,ith o% o-ygen to %orm 3arbon Dio-ide and ,ater. They are both thermal( o-idation processes.
The L'3O 3!-5: total organic carbon analyBer also operates by a thermal o-idation process.
Pyrolysis is a &ery di%%erent %orm o% thermal decomposition. /n pyrolysis( a compound is heated in an enclosed space( to a temperature
usually much higher than that in&ol&ed in combustion. The enclosed space contains no o-ygen( so that thermal decomposition is not
accompanied by o-idation. The hydrocarbon compound is simply broken do,n( or cracked( into simpler and lighter carbon and hydrogen
containing %ragments. The only o-ygen in&ol&ed is that originally contained in the source material( and liberated by the cracking process.
At less e-treme temperatures( and o&er much. Much longer periods o% time( this is &ery much the same process by ,hich organic debris in
sediments matures to kerogen and( e&entually( to oil and gas.
A Pyro-analyBer pro&ides su%%icient controlled heating to emulate those maturation or cracking processes( and then the %ragmentary
products o% pyrolysis are s,ept %rom the chamber by a stream o% an un-reacti&e( inert gas to &arious types o% gas detectors.
#or se&eral years( accelerated pyrolysis( at higher temperatures has been a popular laboratory techni1ue %or the study o% petroleum
maturation processes( and their intermediates and product yields see ?arker0 *1.5$.
/n the late 5496s( ,ork per%ormed at the /nstitut #rancais du PetrolQ /#P( the #rench Petroleum /nstitute$ and the P'T!O#/<A research
center in Melgium led to the de&elopment o% an analytical instrument that used pyrolysis to make measurements indicati&e o% source rock
1uantity and 1uality in a single analysis see !spitalie et al0 *1..$.
Iarious &ersions o% the /#P-P'T!O#/<A de&ice kno,n as the !ock-'&al
G
,ere manu%actured in #rance( and the ?SA by )eocom also
kno,n as )eomechani1ue$ and D'LS/ also kno,n as )irdel( and Delsi-<ermag$ The latest &ersion that / kno, o%$ is the !ock-'&al =(
manu%actured by Iinci Technologies in #rance.
The !ock-'&al pyro-analyBer ,orks by heating a %ormation sample in an inert helium atmosphere.
As temperature rises2
✔ #irst( %ree hydrocarbons are liberated %irst %rom the sample( then
✔ Then( source material is cracked to liberate %ree Hydrogen ,hich rapidly combines ,ith 3arbon and produces light alkanes in
amounts indicati&e o% the hydrogen richness o% the source rock(
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✔ Any o-ygen ,ithin the source rock combines ,ith carbon and is liberated as 3arbon Dio-ide( and
✔ #inally( a%ter all o% the Hydrogen and O-ygen ha&e combined ,ith carbon( and been remo&ed as alkanes and 3arbon Dio-ide( any
surplus carbon in the source material remains as an elemental carbon residue.
#igure 5>2 The !ock-'&al pyro-analyBer heats a cuttings sample in a helium atmosphere( detects %ree hydrocarbons(
kerogen abundance( type and maturity.
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The relati&e amounts o% gases produced( and the temperature o% peak e&olution are compared ,ith a database o% results %rom a large
number o% standard rock samples prepared by the /#P. #rom this comparison( it is possible to make semi-1uantitati&e deductions about the
organic richness and maturity o% source rocks.
The original !ock-'&al does not detect the total carbon in the sample( only that ,hich combines ,ith hydrogen or o-ygen to escape as
gases. /t is &ery con&enient to run both TO3 and !ock-'&al de&ices together and process sample batches in parallel to gi&e measures o%
the total 3arbon( Hydrogen and O-ygen content and( as ,e@ll see( the diagnostically signi%icant ratios o% those elements.
Sample preparation %or the !ock-'&al is similar to that used %or TO3 analysis e-cept that acid ,ashing is not necessary because the !ock-
'&al does not heat the sample to high enough temperatures %or carbonate-cracking to occur.
Although the pyrolytic heating and analysis program is more comple- that the TO3 analysis( it is controlled in the !ock-'&al instrument by a
microprocessor controller %or each o% the stages o% heating and gas analysis. The de&ice can e&en be loaded ,ith se&eral pre-,eighed
samples and le%t to run unattended %or up to eight hours.
The basic !ock-'&al program ,orks like this2
✔ The sample is loaded into the !ock-'&al o&en( and it is %irst heated up to a constant o&en temperature o% ;66U3 as the system is
purged ,ith inert helium.
✔ The helium %lo, is maintained as o&en temperature is programmed to rise at :8U3 per minute( up to a ma-imum temperature o%
886U3 see Figure *1$.
During this heating program2
✔ #ree hydrocarbons in the sample mainly oil ,ith a little remaining gas$ is dri&en o%%( carried along ,ith the helium %lo,( and detected
by the #/D %lame ioniBation$ detector see #tep * in Figure *2$.
This is displayed as the #* Peak in Figure *1$.
✔ At higher temperatures( kerogen in the sample is cracked to yield more hydrocarbons ,hich is also detected at the %lame ioniBation
detector #/D$ see #tep + in Figure *2$.
This is displayed as the #+ Peak in Figure *1$.
✔ 3arbon Dio-ide( deri&ed %rom the cracking o% o-ygen-rich kerogen is trapped in a chemical trap see #tep , in Figure *2$ to be
released later by heating and detected at a thermal conducti&ity detector see #tep 5 in Figure *2$.
This is displayed as the #, Peak in Figure *1$.
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Mased upon calibration ,ith /#P-prepared and certi%ied organic standards and pure compounds( the gas peaks are directly reported
as milligrams per gram o% rock.
#igure 542 !esults %rom the !ock-'&al pyro-analyBer indicate the presence o% %ree hydrocarbons( and the abundance(
type and maturity o% kerogen %rom the parameters S5( S:( S; and T
ma-.

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✔ With increasing kerogen maturity( the !ock-'&al needs to add more and more heat to the sample be%ore it begins to crack and
liberate the #
+
hydrocarbons. The o&en temperature in degrees 3entigrade( T
ma-
( at ,hich the ma-imum o% the #
+
Peak occurs see
#tep / in Figure *2$ is recorded and reported as a measure o% kerogen maturity.
This is displayed as &
ma$
in Figure *1$.
The #
*
peak has similar signi%icance to the cuttings lender test( re%lecting the %ree hydrocarbons retained in the cuttings. /t is more
reproducible( ho,e&er( because it uses a precisely ,eighed and uni%ormly processed sample. Mecause o% the time delay in storage and
processing in&ol&ed( the S
5
result is unlikely to include any o% the &ery lightest hydrocarbon gases.
The #
*
peak increases ,ith the total amount o% the kerogen in the rock but it also re%lects the maturity and hydrocarbon yield o% the kerogen.
#rom the #
*
and #
+
peaks together( a hydrocarbon production inde$( e-pressed as a %raction o% the total hydrocarbon producti&ity o% the
sample( may also be calculated. This is a measure o% ho, much hydrocarbon has already been generated #
*
$( compared to the total
amount o% hydrocarbons that could be generated #
*
and #
+
$ %rom the organic content o% the rock2
;;;;;;;;;;;;;;;;;;;;; !Cuation *
✔ /mmature source material ,ill ha&e a &ery lo, &alue o% production inde-( because hydrocarbon generation has not yet begun #
*
is
&ery lo,$.
✔ With increasing maturity( the production inde- increases as #
*
gets higher$( but
✔ /t may decline again in post-mature source beds ,here the produced oil and gas ha&e long ago all been generated. Most o% them ,ill
ha&e already migrated a,ay( and are no more are being replaced ,ith ne,ly generated hydrocarbons.
✔ The &ery highest &alues o% production inde-( perhaps as high as *;>> because #
+
is Bero$ occur in reser&oirs that ha&e little or no
source material but a large accumulation o% %ree hydrocarbons %rom other sources.
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The S
:
peak alone can pro&ide a guide to the total hydrocarbon yield to be e-pected %rom the source bed see Figure +>$. Ho,e&er( this
%igure combines both the amount o% organic matter in the rock and the producti&ity o% that matter.
'
%
Peak
:2g Ag of Organi! Carbon;
'our!e 9ed Bualit
Less than %-- $as 'our!e
%-- to /-- Oil = $as 'our!e
$reater than /-- Oil 'our!e
#igure :62 The S
:
peak alone is a measure o% potential hydrocarbon yield o% the ,hole rock.
Alternati&ely( i% TO3 data are also a&ailable( a true Hydrogen )nde$ may be calculated( and this is independent o% the amount o% organic
material in the rock( responding only to the kerogen type and richness.
;;;;;;;;;;;;;;;;;;;;; !Cuation +
A similar "$ygen )nde$ may be calculated %rom the S
;
peak2
;;;;;;;;;;;;;;;;;;;;; !Cuation ,
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Figure +* sho,s the relationship bet,een these 1uantities( source bed 1uality and kerogen type.
Hdrogen ?nde@
'
%
ATOC
:2gAg of Organi! Carbon;
O@gen ?nde@
'
/
ATOC
:2gAg of Organi! Carbon;
'our!e 9ed Tpe
Less than %-- $reater than 1-- $as 'our!e
%-- to /-- ,- to 1-- Oil = $as 'our!e
$reater than /-- Less than ,- Oil 'our!e
#igure :52 The S
:
and S
;
peaks together ,ith the TO3 &alue are a measure o%
kerogen type and maturity
Peaks S
:
and S
;
are indicati&e o% the amount o% kerogen present in the rock and its hydrogen
and o-ygen content respecti&ely. The relati&e richness o% hydrogen and o-ygen in the
kerogen indicates the type and yield o% hydrocarbons to be e-pected %rom it see Figure +*$(
and can be illustrated in a Ian Jre&elen diagram see Figure ++$.
The ratio o% S
:
to S
;
is a measure o% the slope o% the lines representing kerogen types in the
Ian Jre&elen diagram and can gi&e a general indication o% the kerogen type and likely
hydrocarbon production see Figure +,$.
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#igure ::2 The Ian Jre&elen diagram relates Hydrogen /nde- S
:
KTO3$ and O-ygen /nde- S
;
KTO3$ ,ith source type
and maturity
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#igure :;2 The relati&e richness o% Hydrogen re%lected in the #
+
peak$ and O-ygen re%lected in the #
,
peak$ in the
kerogen is diagnostic o% the type and yield o% hydrocarbons to be e-pected %rom it
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Mecause o% the di%%erence in time scale( the o&en temperature at ma-imum hydrocarbon e&olution( &
ma$
( has no meaning%ul relationship to
the actual %ormation maturation temperature. Ho,e&er( by correlation ,ith the /#P database o% standard samples( an e1ui&alent &
ma$
"il
Windo' can be de%ined see Figure +5$.
T
2a@
:
o
C; Produ!ti#it 7Windo58
Less than &/, $as 'our!e
&/, to &1- Oil = $as 'our!e
&1- to ,-- Oil Windo5
$reater than ,-- Post-2ature
#igure :72 #rom correlation ,ith the /#P database( Tma- can be used to indicate maturity o% the source bed
The !ock-'&al data( ,ith TO3 and associated mud log data are plotted on the special ,ell-site geo-chemical log %ormat see Figure +/$.
The process o% thermal decomposition is not a series o% predictable( stoichiometric chemical reactions. The analysis is ne&er completely
reproducible and( in %act( calibration is per%ormed by ad0usting instrument parameters until correct results are obtained matching the /#P
standard source rock samples. T,o or more calibration standard samples are included ,ith e&ery batch o% drilled samples and( i% t,o
machines are being used to process the samples one at the ,ell site( and another at a base laboratory$ inter-calibration samples must also
be run on a daily basis see ClemenB0 7emaison0 and 7aly0 *1.1$.
Some ob0ections ha&e been lodged against the &alidity and reproducibility o% !ock-'&al %or a number o% reasons( such as2
✔ Thermal decomposition is catalyBed by clay minerals in the rock matri-. An abundance o% high 3'3 clays ,ill enhance reaction in the
!ock-'&al o&en( increasing hydrocarbon yield( or achie&ing peak hydrocarbon e&olution at a lo,er T
ma-
see Figure +6$.
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✔ Some less common carbonates decompose and yield 3arbon Dio-ide belo, 886U3. Presence o% these carbonates in trace 1uantities
,ith calcite and dolomite may initiate e&en these more stable carbonates to partially decompose. The e&olution o% 3arbon Dio-ide
%rom carbonates ,ill cause a broadened or %alsely high S
;
peak( and a pessimistic O-ygen /nde-( S
;
KTO3 see Figure +.$.
✔ Some bitumens( tars and hea&y petroleum residues( may ha&e a lo, &olatility and re1uire higher temperatures and longer cracking
be%ore they to are e&ol&ed and detected. /nstead o% %orming part o% the S
5
peak( they ,ill merge ,ith the kerogen-deri&ed
hydrocarbon( producing a broadened S
5
or S
:
peak. Alternati&ely this may also result in a mis-identi%ied S
:
peak and pessimistic
Hydrogen /nde-( S
:
KTO3( and kerogen indication( and perhaps e&en a %alsely lo, T
ma-
maturity indication see Figure +2$.
#igure :82 The ,ell-site geo-chemistry log displays !ock '&alG pyro-Analysis( TO3 or associated mud log and geo-
chemical data and may be used to monitor source rock and reser&oir occurrence( type and maturity.
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#igure :=2 The !ock-'&al source bed
e&aluation may be modi%ied by the presence o%
other non-source materials( such as catalytic(
high 3'3 smectite clays that can enhance
reaction in the !ock-'&al o&en( increasing
hydrocarbon yield( or achie&ing peak
hydrocarbon e&olution at a lo,er T
ma-
.
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The 5R plotted !n the same trac) as T The 5R plotted !n the same trac) as T
ma& ma&
!n !n Figure 25 Figure 25 re"ers to 5!tr!n!te Re"lectance( Th!s method, "!rst developed !n coal e&plorat!on, has re"ers to 5!tr!n!te Re"lectance( Th!s method, "!rst developed !n coal e&plorat!on, has
become the most !mportant method "or determ!n!ng sorce bed matr!ty and h!story, by !ts e&cellent correlat!on #!th the ma&!mm become the most !mportant method "or determ!n!ng sorce bed matr!ty and h!story, by !ts e&cellent correlat!on #!th the ma&!mm
"ormat!on temperatre e&per!enced by )erogen( 5!tr!n!te Re"lectance measrements re+!re the se o" a photometer-e+!pped "ormat!on temperatre e&per!enced by )erogen( 5!tr!n!te Re"lectance measrements re+!re the se o" a photometer-e+!pped
petrograph!c m!croscope, and !s not #ell-s!ted to #ell-s!te operat!ons (part!clarly dsty, and v!brat!ng env!ronments @ l!)e md logg!ng petrograph!c m!croscope, and !s not #ell-s!ted to #ell-s!te operat!ons (part!clarly dsty, and v!brat!ng env!ronments @ l!)e md logg!ng
n!ts$) n!ts$)
The T The T
ma& ma&
o!l #!ndo# o" ABC-to-C>> o!l #!ndo# o" ABC-to-C>>
o o
C correlates #ell #!th 5!tr!n!te Re"lectance vales o" >(C-to-/(/D C correlates #ell #!th 5!tr!n!te Re"lectance vales o" >(C-to-/(/D( (
The On-line Mud Logging Handbook Alun Whittaker
#igure :92 The !ock-'&al source bed e&aluation may
be modi%ied by the presence o% other non-source
materials( such as unstable 3arbonates. These may
initiate decomposition o% stable carbonates at lo,er
temperatures( causing a %alsely higher and ,ider S
;
peak( and a pessimistic O-ygen /nde-
#igure :>2 The !ock-'&al source bed e&aluation may be
modi%ied by the presence o% other non-source materials( such
as dense( in&olatile bitumens resulting in ,idened( and
partially merged S
5
and S
:
peaks.
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These %actors( could cause serious concern i% !ock-'&al results ,ere to be taken alone as ha&ing absolute meaning in %ormation e&aluation.
/n reality( like all mud log hydrocarbon results( !ock-'&al data has only comparati&e &alue. Single &alues can ne&er be used alone. The
trend o% data through a ,hole section is used in combination ,ith all other measurements and obser&ations( to make ,ell-to-,ell or Bone-to-
Bone correlations. ?sed in this manner( possible errors can be acceptable though sometimes troublesome$ in a ,ell-site screening tool.
There are other( more practical ob0ections to using the !ock-'&al and TO3 analyBer at the ,ell site. The machines are &ery large( &ery
e-pensi&e and produce great amounts o% ,aste heat. The complicated sample preparation procedure is time consuming and more suitable
%or large batch processing than %or the sample-by-sample( real-time schedule o% mud logging.
Se&eral alternati&e de&ices ha&e been introduced that attempt to simpli%y or reduce the cost o% ,ell-site geo-chemistry. These include2
✔ Oil Sho, AnalyBerG OSA$( or !ock-'&al /// %rom D'LS/ Figure ,*$(
✔ Thermolytic Hydrocarbon AnalyBerG THA$ de&eloped by L'3O ,ith '-ploration Logging 'HLO)$ Figure ,+$(
✔ PyrologgerG %rom )eoser&ice Figure ,,$( and
✔ !ock-'&al = %rom Iinci Technologies Figure ,5$.
The di%%erences bet,een these de&ices and the original TO3 Figure +1$ and !ock-'&al Figure ,>$ are sho,n belo,.
#igure :42The L'3O 3!-5: measures only total
organic carbon TO3$ in the source rock.
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#igure ;62 The !ock-'&al / and // di%%er only in electronics and processor design. The measurements are essentially the
same2 S
5
( S
:
( S
;
peaks and temperature T
ma-
.
#igure ;52 The Oil Sho, AnalyBer( or !ock-'&al ///( measures 3arbon Dio-ide %or total organic carbon TO3$ content(
and not %or kerogen O-ygen /nde-.
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#igure ;:2 The Thermolytic Hydrocarbon AnalyBer is a simpli%ied pyro-analyBer( indicati&e o% ,hat may become the ne-t
generation mud logging analyBer.
#igure ;;2 The Pyrologger is a another candidate to be the ne-t generation mud logging analyBer.
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The ne,er de&ices ha&e numerous bene%its and dra,backs. Ho,e&er( in summary2
✔ The Oil Sho, AnalyBer and the !ock-'&al ///( see Figure ,*$ attempt to combine the %unctions o% the !ock-'&al and Total Organic
3arbon analyBer( but in doing so they pay the price o% losing the originalDs S
;
O-ygen /nde- peak.
The OSA also has a lo,er temperature stage to the temperature program allo,ing the S
5
( %ree hydrocaron( peak to be subdi&ided
into an S
6
( %ree gas peak and an S
5
D( %ree oil peak.
?n%ortunately( this bonus is probably lost because the time-consuming sample grinding( acidi%ication necessary to eliminate
carbonate minerals contamination o% the TO3 peak$( and air drying steps. /t is likely that( during these processes( e&aporati&e loss o%
%ree gas %rom the sample ,ill be completed long be%ore the it reaches the pyrolysis o&en.
✔ The Thermolytic Hydrocarbon AnalyBer THA( see Figure ,+$ and Pyrologger see Figure ,,$ are simpler de&ices that attempt to
reduce the cost and comple-ity o% the de&ices ,hile speeding up the analysis. <either de&ice is e1uipped %or automatic sample
handling and part o% the simpli%ication %or both includes an easier( 1uicker and partly automated sample processing( using a %i-ed
&olume rather than mass$ o% pressure dried rather than air dried$ sample.
Like the OSA( the THA adds a lo,er temperature stage to the temperature program producing S
6
( %ree gas( peak and S
5
D( %ree oil(
peaks. ?nlike the OSA( the less e-treme and 1uicker sample processing allo, these peaks to be more &alid( and use%ul in source
and reser&oir e&aluation.
✔ The !ock-'&al = see ?ehar0 +>>*( and Figure ,5$ apparatus is the latest &ersion o% the !ock-'&al product line( de&eloped in 544=
by Iinci Technologies. /t is more comple-( automated( and e-tensi&ely programmable de&ice best suited to a standalone %ield
laboratory than a mud logging unit.
My &arying itDs program( the !ock-'&al = can determine any o% the parameters a&ailable to all o% the other pyro-analysis de&ices( and
more.
Sample processing and 1uality is impro&ed because acidi%ication is not re1uired. The !ock-'&al = temperature programming allo,s
3arbon Dio-ide and 3arbon Mono-ide %rom the pyrolysis o% organic and mineral sources to be separated and independently
analyBed using an in%rared /!$ gas detector. /t can also measure 3arbon Dio-ide and mono-ide created by o-idation in the high
temperature TO3$ phase o% the analysis. The !ock-'&al output parameters are sho,n in Figure ,5.
!emembering the non-stoichiometric nature o% sample pyrolysis( it is not surprising that analytical results %rom any o% these pyro-analyBer
are rarely in e-act agreement ,ith each other. As mentioned be%ore( i% t,o or more de&ices o% the same or di%%erent types$ are being used(
then inter-calibration samples must run regularly and machines ad0usted to gi&e compatible results.
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Para2eter .nit 'our!e
'
1
2g HCAg ro!k
6ree hdro!arbons in heliu2 gas strea2* 2easured at 6?3 :fla2e
ioniCation; dete!tor
'
%
2g HCAg ro!k
Hdro!arbons fro2 prolsis of organi! sour!e 2aterial in heliu2 gas
strea2* 2easured at 6?3 :fla2e ioniCation; dete!tor
Tp'
%
DC Measured sa2ple te2perature at 2a@i2u2 of '% peak>
'
/
2g CO
%
Ag ro!k
Carbon 3io@ide fro2 prolsis of organi! sour!e 2aterial in heliu2 gas
strea2* 2easured at ?E :infra-red; dete!tor
'
/
F
2g CO
%
Ag ro!k
Carbon 3io@ide fro2 de!o2position of !arbonate 2inerals in heliu2 gas
strea2* 2easured at ?E :infra-red; dete!tor
Tp'
/
G DC Measured sa2ple te2perature at 2a@i2u2 of '
/
H peak>
'
/
CO 2g COAg ro!k
Carbon Mono@ide fro2 prolsis of organi! sour!e 2aterial in heliu2 gas
strea2* 2easured at ?E :infra-red; dete!tor
Tp'
/
CO DC Measured sa2ple te2perature at 2a@i2u2 of '
/
CO peak>
'
/
GCO 2g COAg ro!k
Total Carbon Mono@ide fro2 prolsis of both organi! sour!e 2aterial
and de!o2position of !arbonate 2inerals in heliu2 gas strea2*
2easured at ?E :infra-red; dete!tor
#igure ;72 Measured and computed parameters a&ailable %rom the programmable !ock-'&al =.
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Para2eter .nit 'our!e
'
&
CO
%
2g CO
%
Ag ro!k
Carbon 3io@ide fro2 o@idation of organi! sour!e 2aterial in o@gen gas
strea2* 2easured at ?E :infra-red; dete!tor
'
,
2g CO
%
Ag ro!k
Carbon 3io@ide fro2 de!o2position of !arbonate 2inerals 2aterial in
o@gen gas strea2* 2easured at ?E :infra-red; dete!tor
Tp'
,
DC Measured sa2ple te2perature at 2a@i2u2 of '
,
peak>
'
&
CO 2g COAg ro!k
Carbon Mono@ide fro2 o@idation of organi! sour!e 2aterial in heliu2 gas
strea2* 2easured at ?E :infra-red; dete!tor
T
2a@
DC Co2puted fro2 Tp'
%
Produ!tion ?nde@ :P?;
ProlCable Organi!
Carbon :PC;
I b 5eight Co2puted fro2 '
1
* '
%
* '
/
* '
/
CO* and '
/
GCO:
Eesidual Organi!
Carbon :EC;
I b 5eight Co2puted fro2 '
&
CO and '
&
CO
%
Total Organi!
Carbon :TOC;
I b 5eight Co2puted fro2 PC and EC
#igure ;7 continued$2 Measured and computed parameters a&ailable %rom the programmable !ock-'&al =.
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Para2eter .nit 'our!e
Hdrogen ?nde@ :H?; 2g HCAg TOC
O@gen ?nde@ :O?; 2g CO%Ag TOC
Mineral Carbon
:MinC;
I b 5eight Co2puted fro2 '
/
G* '
/
GCO and '
,
#igure ;7 continued$2 Measured and computed parameters a&ailable %rom the programmable !ock-'&al =.
Pyro-analyBer technology continues to e&ol&e. As yet there is no consensus on the optimum group o% capabilities and acceptable limitations.
Ho,e&er( it appears likely that %urther de&elopments ,ill continue the parallel trends to,ard more capable laboratory instruments( like the
!ock-'&al =( and simpler( more rugged ,ell-site instruments( like the Pyrologger. Figure +/ demonstrates that pyro-analysis can de&elop
data and in%ormation that is compatible ,ith mud logging and enhances the standard measurements in a manner that can truly be called
ad&anced or ne-t generation mud logging. / con%idently predict that some %orm o% pyro-analysis ,ill become a standard %eature o% mud
logging.
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Temperature Programmed 3hromatography
More sophisticated laboratory chromatographs also use temperature programming. Temperature-programming e-tends the range o% ,ell-
site chromatography( allo,ing the &olatiliBation and separation o% many higher alkanes and more comple- hydrocarbons. The sample port
and columns are heated through a controlled range o% temperature during analysis( This is not intended to crack or decompose
hydrocarbons but to increase the &olatility o% hea&ier components( and impro&e chromatographic separation o% e-isting lighter components.
#igure ;82 Temperature-programmed chromatography can pro&ided e-tended hydrocarbon analyses allo,ing
recognition o% reser&oir character and producti&ity( %or e-ample( petroleum condensate or ,et gas.
With impro&ed reliability and reduced cost o% technology( this type o% chromatograph is becoming a&ailable %or use at the ,ell site. /t is no,
possible to e-tract oil( gas and bitumens %rom cuttings samples and to obtain a chromatogram representing the entire %luid composition. As
mentioned earlier in this chapter( ,ith more components in the chromatogram it becomes easier to identi%y %luids %rom di%%erent reser&oirs(
source beds and oil-mud contaminants see Figures ,/( ,6( ,. and ,2$.
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#igure ;=2 Temperature-programmed chromatography o% a high
gra&ity light and &olatile$ oil.
#igure ;92 Temperature-programmed chromatography o% a
lo, gra&ity dense and hea&y$ oil.

#igure ;>2 Temperature-programmed chromatography o% a &ery dense(
immo&able residual oil. residual oil
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On the other hand( despite impro&ements2
✔ These temperature-programmed chromatographs are still large( e-pensi&e and delicate machines( and
✔ They need skilled and attenti&e operators( and a good deal o% time to prepare and run the specialiBed samples re1uired.
✔ The output o% the de&ices( although un1uestionably in%ormati&e( is also comple- and re1uires care%ul and kno,ledgeable
interpretation.
✔ #inally( the data produced %rom these machines ,ill probably be re1uired only through limited sections o% a ,ell or on limited ,ells
o% an e-ploration and de&elopment program.
All-in-all( there are %e, strong arguments %or putting this type o% e1uipment at the ,ell site. Only logistic or political di%%iculties ,ould 0usti%y the
e-pense and personnel necessary to dedicate this type o% e1uipment to a single rig.
Pyro-chromatography
A %urther de&elopment in gas analysis has been the coupling o% a simple pyrolysis de&ice to a chromatograph. Pyro-gas-chromatography
combines a simple pyro-analyBer ,ith a chromatograph.
✔ #ree hydrocarbon components that comprise the S
5
peak can be separated and displayed as a chromatogram much like that seen in
temperature programmed chromatography see Figure ,1$.
✔ Jerogen is thermally cracked and the gases %rom the S
:
peak can be separated and displayed in the same ,ay. Mecause the
components in the S
:
peak did not e-ist in the sample %ormation %luids( but are ne,ly created in the pyro-analyBer( this is re%erred to
as a %ragmentogram see Figure 5>$.
'-amples o% pyrolysis-gas-chromatography are sho,n in #igure ;4 and #igure 76. There is( again( no doubt that these data are in%ormati&e.
Ho,e&er( these e-amples may be misleadingly simple. /n practice( the results may be o% little diagnostic &alue at the ,ell site. / doubt that
this is the type o% data that is re1uired in real-time or that can be reliably interpreted in the time or ,ith the personal skills a&ailable ,hile
drilling. These are specialiBed tools more suited to the research laboratory. Me%ore they %ind a place at the ,ell site( ,e ,ill need to %ind
better and simpler means o% understanding and interpreting them.
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#igure ;42 A pyro-chromatogram o% the S
5
peak %rom a pyroliBed source bed sample.
#igure 762 A %ragmentogram o% the S
:
peak
%rom a pyroliBed source bed sample.
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Worst 3ase Scenario
Oil-based drilling %luids ha&e been used on-and-o%% throughout the history o% rotary drilling. They ha&e al,ays been unpleasant to ,ork ,ith.
and the cause o% serious di%%iculties in %ormation e&aluation. ?n%ortunately %or the geologist$ they ha&e al,ays been able to sol&e di%%icult
and e-pensi&e drilling problems caused by chemical reaction bet,een a ,ater-based drilling %luid and e-posed %ormations.
/n the late si-ties and se&enties( ,e thought that the problem had been sol&ed %or us. /ncreases in e-ploration o%%shore coupled ,ith greater
en&ironmental concern and regulation almost managed to put and end to oil-based muds. /n order to use the muds o%%shore( and e&en in
some onshore locations( re1uired complicated and e-pensi&e clean-up e%%orts to pre&ent oil-coated cuttings %rom polluting the area around
the rig. The cost o% these acti&ities o&er,helmed the sa&ings achie&ed by using the oil-based mud. Oil-based muds became rare. /n many
cases( ,ater-based mud systems and additi&es ,ere de&eloped to cope ,ith the same problems although( admittedly( not 1uite so ,ell and
usually more e-pensi&ely.
Since the nineties( there ,as been a resurgence in the use o% oil-based muds ,ith the de&elopment o% the so-called en&ironmentally sa%e oil-
based mud materials. ?sually based upon mineral oils also kno,n as ,hite oil( li1uid para%%in( or de-aromatiBed kerosene$( and modi%ied
&egetable( or %ish oils( these may contain pure( high molecular ,eight alkanes or poly-alicyclic compounds. They are lo, in &olatiles and
aromatics( and are claimed to be harmless to the en&ironment and inert in %ormation e&aluation.
As ,e ha&e discussed in pre&ious chapters( these muds ha&e pro&en to be as much o% a problem %or mud log interpretation as the older
to-ic oil muds. There ha&e been many arguments regarding the possibility o% cracking o% the oils by do,n-hole temperature and clay
catalysis to %orm lighter( more &olatile alkanes. /t does appear that it is most o%ten in areas o% higher geothermal gradient that use o% mineral
oil muds is associated ,ith anomalously high total hydrocarbons backgrounds.
Ho,e&er( the real problem ,ith the muds is their a%%inity %or dissol&ing %ormation hydrocarbons and their ability to carry high backgrounds o%
oil and gas %rom disparate( multiple origins. These backgrounds can be carried o&er long periods through a ,ell or e&en %rom ,ell to ,ell. /n
some cases( mud logging %ormation e&aluation becomes almost meaningless. /% a ,ell is spudded ,ith a drilling %luid system already
containing all o% the oils and gases anticipated %or the ,ell( log interpretation becomes( at best( dubious( regardless o% the 1uality o%
e1uipment and personnel.
Throughout this period the mud chemical manu%acturers continued to congratulate themsel&es on the per%ection o% their products ,hile the
mud logging contractors ,ere bombarded ,ith demands %or a solution to the problem. There has been e-perimentation ,ith se&eral
techni1ues attempting to %ind means o% identi%ying an oil or gas sho, in the presence o% this massi&e and broad-based contamination. Some
achie&ed partial success but at unacceptably high cost. <one o% them ha&e had any more degree o% success than the good logging
procedure and logical data e&aluation discussed in pre&ious chapters.
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/% things ,ere not bad enough( a signi%icant stimulant to the resurgence o% oil-based mud has been the increased incidence o% &ery high
angle drilling. /n these steeply angled( and e&en horiBontal ,ells( the problems associated ,ith drill string %riction and sticking in the bore
hole are increased by orders o% magnitude. The much greater lubricity o% oil-based drilling %luids is a great bene%it in reducing drill string
,ear( damage and sticking in the bore hole. This good ne,s %or the driller translates into the ,orst possible ne,s %or the mud logger.
!ecognition o% %ormation tops %rom drilling breaks( cutting lithology and gas sho,s all become more di%%icult ,hen drilling horiBontally( or at a
high angle through the section2
✔ !OP becomes less responsi&e to changes in %ormation drillability ,hen much o% the drill-string ,eight is resting on stabiliBers and
rotary reamers on sections o% the bore-hole ,all.
✔ ?nderstanding the mi-ing o% cuttings and gas in the drilling %luidDs laminar or turbulent %lo, becomes e&en more di%%icult ,hen %or
much o% the bore hole( mud %lo, is horiBontal so that annular &elocity pro%iles and cuttings settling %orces are acting &ertically across
the bore hole.
✔ /ncreased %riction o% the drill collars( stabiliBers and rotary reamers adds to increased damage to the bore-hole ,all and
contamination o% the mud stream ,ith ca&ings and other debris. All this material is sub0ect to %rictional grinding bet,een the drill string
and bore-hole ,all making the cuttings more di%%icult to use( and ca&ings are ground smaller( and less easy to discriminate %rom
cuttings.
✔ When these problems are compounded by the use o% an oil-based drilling %luid carrying a high and regularly recycling background o%
oil a gas( you ha&e the ,orst possible case %or mud logging.
/t is unlikely that pre&enting mud logging di%%iculties is going to be a ma0or consideration in the %uture use o% either horiBontal drilling or oil-
based drilling %luids. So( it is up to us to %ind better ,ays o% doing mud logging in those circumstances. /n this chapter ,e ha&e looked it
some tools( such as %luorimetry( re%ractometry and pyro-analysis( that can make a small( though possibly important impro&ement to routine
%ormation e&aluation. Perhaps( one or more o% these techni1ues can pro&ide the e-tra component that sol&es our problem ,ith horiBontal
drilling and oil-based drilling %luids.
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The S,an Song
When / told people that / ,as ,riting this book( the standard reaction ,as2
VWhat are you going to say about oil-based mud and horiBontal drillingAW. Well. ,hat / ha&e to say is this( there are t,o easy ans,ers to
%ormation e&aluation in oil-based mud2
✔ !asy Ans'er -*= VDonDt use the stu%%.W
✔ !asy Ans'er -+= V/% you must( then plan on coring all potential pay Bones.W
That may sound unrealistic and academic but it is also true. /% the oil-based mud is sa&ing so much money( then ,hy not spend a little o% it
curing the disaster it ,recks on %ormation e&aluationA
/% you must add something to the mud logging unit( try the Atago re%ractometer. #rom practical e-perience( / ,ould claim the re%ractometer to
be at least as reliable as synchronous scanning %luorimetry in identi%ying oil sho,s. This is still not &ery good2 about 76 to =6 percent. On the
other hand it costs only about one hundredth the price o% a %luorimeterL
And <e-t
/n the ne$t chapter( ,e are going to look at drilling monitoring sensors and systems that ha&e proli%erated in mud logging units o&er the last
%e, years. The primary purpose o% these systems is to impro&e drilling economy and sa%ety( and the mud logger needs to kno, ho, to
communicate the sensor measurements to the drillers and engineers ,ho need them.
We may also learn a little bit about ho, these data can also pro&ide use%ul in%ormation and interpreti&e assistance to the mud logger and
geologist.
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