ENM201 WELLS
Oil & Gas Well Drilling Part 2.
Prepared and presented by Owen Jenkins, BA, MA, CEng, CMarEng, FEI, MIMarEST.
© Robert Gordon University and Owen S. Jenkins Ltd. 2010
Introduction to Drill Stem Design
● We’ve already seen some of the basic
tools that make up the drill stem ● Let’s see how we use them.
© Robert Gordon University and Owen S. Jenkins Ltd. 2010
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The Work of Drilling – Remember?
● What makes drilling work? ● Weight – gravity ● Weight-On-Bit (WOB) ● Rotation
■ Torque ■ Speed of rotation of the bit
● Energy stored in the rocks
■ Pore pressure
● A means of clearing away the debris
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The Drill String
● Identification of Drill String
Credentials ● Basic Functions ● Yield, Tensile & Torsional Strength ● Rotary Shouldered Connections ● Buoyancy ● Overpull ● Collapse & Burst Pressures ● ‘Neutral Point’ ● Buckling ● Friction Effects in Directional Wells ● REMEMBER – IT’S NORMALLY IN TENSION
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Identification of Drill Pipe
●Data normally stamped on drill pipe to API,
ISO and NORSOK standards: ●1 = Company owning pipe (e.g. KCADeutag) ●2 = Month welded (e.g. 2 = February) ●3 = Year welded (e.g. 01 = 2001) ●4 = Pipe manufacturer and API licence number ●5 = Drill Pipe Grade (e.g. “S”) ●Range Length ●API pipe will also normally bear the API monogram
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Basic Functions
● Transmit and support axial loads ● Transmit and withstand torsional loads ● Transmit fluid under high pressure to
■ Clean the hole ■ Cool the bit ■ Power the MWD pulser and mud motor (if used)
● It must withstand potential fatigue damage
■ ‘Leak before break’ principle
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Stress/Strain Curve
0.2% Proof stress 0.5% Strain
Plastic strain region Elastic limit – Yield Point Elastic region 0.2% strain offset line, parallel to elastic region
0 0.2 0.5% © Robert Gordon University and Owen S. Jenkins Ltd. 2010
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Yield Strength per API Spec 5D
Grade Total Extension of Gauge Length, % 0.5 0.5 0.6 0.7
● Many sources get
this wrong ● They state that API specifies the 0.2% offset ● API Specs 7 and 71 use the 0.2% offset method for tool joints and BHA components, not drill pipe bodies.
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E-75 X-95 G-105 S-135
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Torsional Strength
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Drill Pipe Grades Manufacture
API Grades E-75 (*) X-95 (*) G-105 (*) S-135 (*) Some Proprietary Grades SS-95 G-120 V-150 Min Yield (lbs/in2) 75,000 95,000 105,000 135,000 Min Yield (lbs/in2) 95,000 120,000 150,000 Symbol E X G S Symbol SS-95 G-120 V
Note: (*) denotes commonly used grades of drill pipe
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Drill Pipe Class Inspection
● Per API RP7G Recommended Practice for Drill Stem
Class Number & Colour of Bands Design and Operating Limits (Includes Errata dated May 2000, and Addendum dated November 2003) 16th Edition August 1998 OD Wear Effect / Remaining Pipe Wall Thickness ≥87.5% nom wall 80% 70% <70% N/A
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1 (New) Premium 2 3 Reject
One White Two White One Yellow One Blue One Red
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Which Joint is the Reject?
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Pipe Selection
● When designing the drill string for a well,
plan on using PREMIUM PIPE. ● Even if pipe is new, once it is inspected in service, the highest classification used is PREMIUM, even if the pipe meets Class 1 (new) dimensions. ● Only use pipe of lower class in shallow, non-critical wells. ● We do not use anything less than Premium Class in the North Sea.
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Tensile Strength Example
● What’s the yield strength of 5” Grade G ● ●
19.5 lb/ft Premium Class Drill Pipe? First: Pipe dimensions From tables - API RP7G or other source, e.g. Wilson website (see link later)
1. Find the I.D. or wall thickness of the tube 2. 5” x 19.5 ppf – nominal wall thickness = 0.362”, so: I.D. = 5 – (2 x 0.362) or 4.276” 3. O.D.: 20% WT reduction allowable: so Min. O.D. = 5” – (0.362” x 2 x 0.2) = 5” – 0.01448” = 4.8552”
© Robert Gordon University and Owen S. Jenkins Ltd. 2010
ID
Min. Premium OD Class 1 New OD
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Tensile Strength Example
● What’s the yield strength of 5” Grade G, ● ● ● ●
19.5# Premium Class Drill Pipe? Second: Cross Sectional Area of Steel = (π/4)(OD2-ID2) = (π/4)(4.85522 – 4.2762) = 4.1538 sq.in. Grade G pipe has a Minimum Specified Tensile Yield Stress of 105,000 psi, so: Yield Strength of Pipe = 105,000 x 4.1538 = 436,149 lbf. Or 436,000 lbf. rounded to nearest 1,000.
Area of pale blue – CSA of 5” 19.5# Premium Pipe = 4.1538 sq.in.
© Robert Gordon University and Owen S. Jenkins Ltd. 2010
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Design Factor (or Safety Factor)
● Such tensile strengths are theoretical values
based on minimum areas, wall thickness, and yield strengths ● Yield strength (as defined in API specs) is not the specific point at which permanent deformation of the material begins but the stress at which a certain total deformation has already occurred ● This deformation includes all of the elastic deformation as well as some plastic (permanent) deformation
© Robert Gordon University and Owen S. Jenkins Ltd. 2010
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Design Factor (or Safety Factor)
● So: if the pipe is loaded to the extent shown
in such tables, it is likely that some permanent stretch will occur; ● Moreover, there are variations in wear and wall thickness, eccentricity etc. ● To allow for these, a design factor of 85% to 90% of the tabulated value is used ● The Operator will define the SF or DF he chooses to use.
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Design Factor (or Safety Factor)
● It may be expressed as:● A percentage e.g. 85% ● A decimal number e.g. 0.85 ●
■ So the Max. allowable stress = Yp x 0.85 Or a figure >1 e.g. 1.18 ■ In which case you DIVIDE the component’s nominal yield strength by the factor to get the maximum allowable load = Yp/1.18 Our design is always based on a percentage of yield strength, NOT ultimate tensile strength.
●
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Tensile Strength Example
● Is that answer good enough? ● That is pure tensile load. ● What about torque? ● What about torque + tension? ● What about internal and external yield due to
pressure differences? ● What about bending? ● What about real life? ● A combination of several of the above, most of the time.
© Robert Gordon University and Owen S. Jenkins Ltd. 2010
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Torsional Yield Strength
● Defined as the resistance of the tube to failure by a ● ● ●
twisting torque or force. The torsional yield strength is based on the shear strength equivalent to 57.7% minimum yield. Considering pipe failure in pure torsion (zero tensile load): API RP7G gives us this formula:Q = 0.096167JYm / D ■ Where Q = Min torsional yield strength, ft-lbs (i.e. lbfft) ■ Ym = Min unit yield strength, psi ■ J = Polar moment of inertia: (π/32)(D4-d4)
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Torsional Yield Strength
● For our 5” 19.5 lb/ft grade G premium
class pipe this is ● Q = 0.096167JYm / D = 0.096167 (π/32)(D4-d4) x 105,000 ÷ D = 0.096167 x.098175(4.85524 – 4.2764) x 105,000 ÷ 4.8552 = 45,200 lbf-ft.
● (or, as it so often called, erroneously, “footpounds”)
© Robert Gordon University and Owen S. Jenkins Ltd. 2010
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Combined Torque and Tension – Pipe Body
● API RP7G gives us this formula for combined
torsion and tension:0.096167 J QT = D
● Where
■ ■ ■ ■ ■ ■
P Y m − A2
2 2
32 = 0.098175( D 4 − d 4 )
J=
π
(D4 − d 4 )
for tubes
QT = minimum torsional yield strength under tension, ft-lb (sic!) J = polar moment of inertia D = outside diameter, inches d = inside diameter, inches Ym = material yield strength (sic), psi P = total load in tension, lbs. and ■ A = cross-sectional area, sq.in.
© Robert Gordon University and Owen S. Jenkins Ltd. 2010
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Combined Torque and Tension – Pipe Body
● Let’s see what this means for our grade G,
5” premium class pipe body
© Robert Gordon University and Owen S. Jenkins Ltd. 2010
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Combined Torque and Tension – Pipe Body
5" G-105 19.5# New, Premium and 90% WT Tube Capability 1.00 SF
600000
500000
19.5 # G-105 Premium Tube
400000
Tension lbf.
19.5 # G-105 New Tube
19.5 # G-105 90% WT
300000
200000
100000
0 0 10000 20000 30000 40000 50000 60000 70000 Torque lbf.-ft.
© Robert Gordon University and Owen S. Jenkins Ltd. 2010
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Tool Joints
● Drill pipe is connected together with TOOL
JOINTS ● These usually conform to API Spec. 7 ● Standard material: 120,000 psi MSYS – 0.2% offset method.
© Robert Gordon University and Owen S. Jenkins Ltd. 2010
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Stress/Strain Curve (Again)
0.2% Proof stress 0.5% Total Strain
For Grades E and X drill pipe. 0.6% for G and 0.7% for S.
Plastic strain region Elastic limit – Yield Point Elastic region 0.2% strain offset line, parallel to elastic region
For tool joints and BHA components
0 0.2 0.5% © Robert Gordon University and Owen S. Jenkins Ltd. 2010
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Tool Joint – Box Connection
Tong space
© Robert Gordon University and Owen S. Jenkins Ltd. 2010
Image edited from FPUK original
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Tool Joint – Box Connection
Box Tool Joint Friction weld External upset Internal upset Pipe body
Rotary Shoulder Thread
Tong space
Hardbanding (optional)
18° tapered load shoulder (for elevators)
Image edited from FPUK original
© Robert Gordon University and Owen S. Jenkins Ltd. 2010
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Rotary Shouldered Connections
● Normal drill stem connections are Rotary
shouldered connections ● The shoulder serves to seal the connection faceto-face and to transmit torque ● The threads are tapered and normally conform to API standards ● There are also proprietary threads and connections, but we shall stay with API for the time being.
© Robert Gordon University and Owen S. Jenkins Ltd. 2010
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Connection Strength
● Torque to yield a rotary shouldered connection
per API RP7G.
Ty = Ym A ⎛ p Rt f ⎞ R f + + ⎜ s ⎟ 12 ⎝ 2π cos θ ⎠ Where
Ty = torque to yield lbf - ft. Ym = material maximum yield strength (stress!), psi. A = cross - sectional area of pin or box, Ap or Ab whichever is smaller. p = lead (pitch) of thread, in. f = coefficient of friction on mating surfaces (normally taken as 0.08) θ = ½ included angle of thread, deg.
© Robert Gordon University and Owen S. Jenkins Ltd. 2010
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Connection Strength
Ty = Ym A ⎛ p Rt f ⎞ + + Rs f ⎟ ⎜ 12 ⎝ 2π cos θ ⎠ Continuing : Rt = C + [C − ( L pc − 0.625 ) × tpr × 112 ] 4 L pc = length of pin, in. the effective radius of the thread
Rs = ¼( OD + Qc ) the effective radius of the shoulder C = pitch diameter of thread at gauge point, in. Ap = Ap = Ab =
π π π
4 4
[(C − B ) 2 − ID 2 ] cross - sectional area of pin withou t relief grooves, or ( DRG − ID 2 ) with relief grooves
2
4
[OD 2 − (Qc − E 2 )] cross - sectional area of box.
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© Robert Gordon University and Owen S. Jenkins Ltd. 2010
Connection Strength
Ym A ⎛ p Rt f ⎞ Ty = + + Rs f ⎟ ⎜ 12 ⎝ 2π cos θ ⎠ Continuing : ID = inside diameter, in. ⎛H ⎞ B = 2⎜ − S rs ⎟ + tpr × 18 × 112 the mean effective height of the thread, in. ⎝2 ⎠ H = thread height height not truncated, in. S rs = thread root truncation, in. tpr = taper, in/ft. OD = outside diameter, in. Qc = box counterbore, in. E = tpr × 3 8 × 112 in.
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Rotary Shouldered Connection
From API RP7G
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Connection Strength
● I’m sure you’ve all memorised that! ● So, that was easy, now
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Make-Up Torque (MUT)
● It is most important that a connection is
done up tight enough. ● It is unusual to have too much torque applied at the surface when making-up connections. ● It is very easy to under-torque a connection ● If you do, it may well try tightening itself down-hole (“downhole make-up”)
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Box Failure From Downhole Makeup
© Robert Gordon University and Owen S. Jenkins Ltd. Courtesy 2010 of FPUK Ltd.
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Make-Up Torque
T = Rt f SA ⎛ p ⎞ R f + + ⎜ s ⎟ 12 ⎝ 2π cosθ ⎠ Where A = cross - sectional area of pin or box, Ap or Ab whichever is smaller. Ap shall be based on pin connections without SRGs. S = recommended make - up stress level, psi.
T = make - up torque lbf - ft.
● You memorised the rest earlier, didn’t
you?
■ You didn’t?! ■ Hock and Shorror!
© Robert Gordon University and Owen S. Jenkins Ltd. 2010
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Allowable Stress
● Maximum make-up stress recommended
by API RP7G in rotary shouldered connections, in weaker of box or pin: ● Tool joints: 60% of minimum tensile yield (= 72,000 psi, for API tool joints) ● BHA components: 62,500 psi, except:
■ 87,500 psi. for 2 7/8 PAC ■ 56,200 psi. for H-90. ■ With a bit of luck, you’ll never need either of these awful connections.
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Combined Torque and Tension in a Connection
Pin tensile failure
NC 50 Connection, 6-5/8" OD x 2.75" ID
1600000 1400000 1200000 Applied Tension 1000000
Shoulder Separation
Box failure – hoop stress
800000 600000 400000 200000 0 0 10000 20000 30000 40000 50000 60000
Recommended Area of Operation
Pin Yield (2)
Pin Yield (1)
Box Yield
Shoulder separation
Pin failure – combined torque and tension
70000
Applied Torsion © Robert Gordon University and Owen S. Jenkins Ltd. 2010
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Combined Diagram for Pipe and Tool Joint
5" G-105 19.5# New, Premium and 90% WT Tube Capability 1.00 SF With NC50 Connections. 6-5/8" x 2¾".
1600000 1400000 1200000
Tension lbf.
19.5 # G-105 Premium Tube 19.5 # G-105 New Tube
19.5 # G-105 90% WT
Shoulder Separation
Pin Yield (2)
Pin Yield (1)
Recommended MUT: 38,000 lbf-ft.
1000000 800000 600000 400000 200000 0 0 10000 20000 30000 40000 50000 60000 70000 Torque lbf.-ft.
Recommended Area of Operation
Box Yield
© Robert Gordon University and Owen S. Jenkins Ltd. 2010
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Easier Ways
● You can look these things up in RP7G, but
it does not include all pipe and connection combinations. ● Try the Grant Prideco Website: ● http://www.grantprideco.com/drilling/produ cts/drilling_products_specsTechs.asp ● You will also find details of their proprietary connections and pipe.
© Robert Gordon University and Owen S. Jenkins Ltd. 2010
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Useful Links
● Drill pipe data:
● http://www.iwilson.com/doc.aspx?fielddoc=prodCatDoc&tabledoc=tb ●
l_product_category_docs&fieldkey=prodCatDocId&valuekey=8&filet ype=application/pdf http://www.iwilson.com/doc.aspx?fielddoc=prodCatDoc&tabledoc=tb l_product_category_docs&fieldkey=prodCatDocId&valuekey=10&file type=application/pdf
© Robert Gordon University and Owen S. Jenkins Ltd. 2010
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References
● For derivation of drill stem strength
formulae:
■ API TR 5C3 Technical Report on Equations and
Calculations for Casing, Tubing, and Line Pipe used as Casing or Tubing; and Performance Properties Tables for Casing and Tubing (replaces Bull 5C2 and Bull 5C3) 7th Edition, December 2008.
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References & Bibliography
● API Spec 5D Specification for Drill Pipe. 5th Edition,
October 2001.
● API Spec 7 Specification for Rotary Drill Stem Elements
(Includes Addendums 1, 2 and 3) 40th Edition, November 2001.
■ Covers tool joints for drill pipe only.
● API Spec 7-1/ISO 10424-1 Specification for Rotary Drill
Stem Elements Petroleum and natural gas industries— Rotary drilling equipment — Part 1: Rotary Drill stem elements (Includes Addendum 1 dated March 2007) 1st Edition February 2006.
© Robert Gordon University and Owen S. Jenkins Ltd. 2010
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References & Bibliography
● API Spec 7-2/ISO 10424-2 Specification for Threading
and Gauging of Rotary Shouldered Thread Connections Petroleum and natural gas industries—Rotary drilling equipment — Part 2: Threading and gauging of rotary shouldered threaded Connections drill-string components. 1st Edition, June 2008.
● API RP 7G Recommended Practice for Drill Stem
Design and Operating Limits (Includes Errata dated May 2000, and Addendum dated November 2003) 16th Edition, August 1998.
© Robert Gordon University and Owen S. Jenkins Ltd. 2010
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ENM201 WELLS
Oil & Gas Well Drilling Part 2.
Prepared by
OWEN S. JENKINS LTD.
4, Charlton Avenue, Aboyne, Aberdeenshire, AB34 5GL, Scotland. Tel. +44 (0)13398 87779. Mobile phone: +44 (0)7803 296779. Email:
[email protected] Website: www.osjl.co.uk
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