Barnett Log Analysis Model, Spears

Devel op ment of a Pre dic tive Tool for Esti mat ing Well Per for mance in
Hor i zon tal Shale Gas Wells in the Barnett Shale, North Texas, USA
Rus sell W. Spears
1
and S. Lance Jack son
1
THE BARNETT SHALE, METROPOLITAN
DALLAS-FORT WORTH, NORTH TEXAS
The Mis sis sip pian Barnett Shale is cur rently under go ing
pro lific devel op ment as a gas resource in and around the
Dal las-Fort Worth area, north east Texas (Fig ure 1). One of
the larg est devel op ment chal lenges to the Barnett Shale has
been its prox im ity to urban areas in and around the greater
Dal las-Fort Worth area. Cre ative devel op ment plans and
oper a tions have been spe cif i cally tai lored to the Barnett
Shale play to min i mize envi ron men tal impact on the area,
includ ing the use of hor i zon tal wells drilled from
multi-well pad sites.
Geo log i cal set ting of the Barnett Shale
Stratigraphically, the Barnett sits uncon form ably above
the Viola and/or Ellenburger For ma tion. The Ellenburger
has seen pro lific pro duc tion in the north Texas area over
many decades. In this par tic u lar study area, the Ellenburger
PETROPHYSICS, VOL. 50, NO. 1 (FEBRUARY 2009); P. 19–31; 15 FIGURES, 4 TABLES
ABSTRACT
Pro duc tion from “uncon ven tional” shale gas res er voirs
has seen increased atten tion and eco nomic via bil ity in
recent years through the use of hor i zon tal devel op ment
wells. Max i miz ing hor i zon tal per me abil ity in such wells
has been found to be one of the larg est keys to unlock ing
shale gas res er voirs and pro duc ing them at eco nomic
rates. Cur rently, a world-class shale gas accu mu la tion is
being devel oped in and around the Dal las-Fort Worth,
Texas, area using hor i zon tal well appli ca tions.
A multi-com po nent approach to derive reli able and
accu rate pre dic tions of hor i zon tal shale gas well per for -
mance is pre sented here, using open hole well log data
from sev eral ver ti cal pilot bore holes that have been
drilled tar get ing the Barnett Shale. Fun da men tally, this
approach is founded upon four key ele ments: a thor ough
proba bil is tic vol ume esti ma tion of lithol ogy, cal cu la tion
of total poros ity, esti ma tion of free gas pres ent using a
mod i fied dual water sat u ra tion model and pre dic tion of
kerogen and total-organic-car bon (TOC) of the inter val.
From the pri mary eval u a tion from open hole logs, net
kerogen-feet, TOC-ft and adsorbed gas-feet have all been
iden ti fied as mean ing ful mea sures of shale “qual ity” that
are use ful as a vehi cle to obtain accu rate pre dic tions of
hor i zon tal well ulti mate recov ery gas vol umes (EUR).
These fac tors have been weighted as a func tion of drilled
lat eral length for the hor i zon tal pro duc tion hole that has
been sub se quently drilled from each pilot. Vary ing the
val ues cal cu lated at the pilot well accord ing to hor i zon tal
length is a key aspect of this eval u a tion tech nique and the
weight ing of these param e ters found to cor re late to
decline-curve based EUR vol umes for the study wells.
The net prod uct has been a reli able indi ca tor for visu al iz -
ing and quan ti fy ing well per for mance in five exist ing
Barnett Shale hor i zon tal wells, using stan dard open hole
well log data acquired in the ver ti cal pilot holes.
Keywords: Shale gas, adsorbed gas, kerogen, pro duc -
tiv ity
Manu script received by the Edi tor Sep tem ber 29, 2008; revi sion manu script received Decem ber 1, 2008.
1
ExxonMobil Pro duc tion Com pany, Hous ton, Texas, USA; Email: rus [email protected]
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