AUTHO RS
Ronald J.Hill $Central Energy Resources Team,U.S.Geological Survey,Box 25046,Mississippi 939,Denver,Colorado 80225;v
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Ronald Hill specializes in petroleum geochem-istry and has more than 12years of profes-sional experience,including his stint in Exxon-Mobil and Chevron.Currently,he is a rearch geologist for the U.S.Geological Survey.His interests include the investigation of shale-gas resources and the process that control pe-troleum generation.He holds geology degrees from Michigan State University (B.S.degree)and the University of California,Los Angeles (Ph.D.),and a geochemistry degree from the Colorado School of Mines (M.S.degree).Etuan Zhang $Shell International Explora-tion and Production Company,Houston,Texas 77001;
Etuan Zhang received a Ph.D.from Pennsylva-nia State University (1994)and joined Chevron as a postdoctoral rearcher in 1994before moving on to Shell in 1997.His rearch is directed toward understanding the kinetics of petroleum generation and investigation of unconventional resources.
Barry Jay Katz $Chevron Corporation Energy Technology Company,Houston,Texas 77002;
Barry Jay Katz received his B.S.degree in ge-ology from Brooklyn College and his Ph.D.in marine geology and geophysics from the Uni-versity of Miami.He has held various tech-nical and supervisory positions in Texaco’s,ChevronTexaco’s,and Chevron’s technology organizations since joining Texaco in 1979.Barry is currently a Chevron Fellow and team leader for hydrocarbon charge in Chevron’s Energy Technology Company.
Yongchun Tang $Petroleum Energy &Environment Rearch Center,California In-stitute of Technology,Covina,California 91722;tang@peer.caltech.edu
Prior to joining the California Institute of Tech-nology,Tang had more than 15years of in-dustrial experience in both upstream and down-stream rearch at Chevron.He is currently the director for the Power Environmental Energy
Modeling of gas generation from the Barnett Shale,Fort Worth Basin,Texas
Ronald J.Hill,Etuan Zhang,Barry Jay Katz,and Yongchun Tang
ABSTRACT
The generative gas potential of the Mississippian Barnett Shale in the Fort Worth Basin,Texas,was q
uantitatively evaluated by aled gold-tube pyrolysis.Kinetic parameters for gas generation and vi-trinite reflectance (R o )changes were calculated from pyrolysis data and the results ud to estimate the amount of gas generated from the Barnett Shale at geologic heating rates.Using derived kinetics for R o evolution and gas generation,quantities of hydrocarbon gas gen-erated at R o $1.1%are about 230L/t (7.4scf/t)and increa to more that 5800L/t (186scf/t)at R o $2.0%for a sample with an initial total organic carbon content of 5.5%and R o =0.44%.The volume of shale gas generated will depend on the organic richness,thickness,and thermal maturity of the shale and also the amount of petroleum that is retained in the shale during migration.Gas that is rervoired in shales appears to be generated from the cracking of kerogen and petroleum that is retained in shales,and that cracking of the retained petroleum starts by R o $1.1%.This result suggests that the cracking of petroleum retained in source rocks occurs at rates that are faster than what is predicted for conventional siliciclastic and carbonate rervoirs,and that contact of retained petroleum with kerogen and shale mineralogy may be a critical factor in shale-gas generation.Shale-gas systems,together with overburden,can be considered complete petroleum systems,although the process of petroleum migration,accumulation,and trap formation are differ-ent from what is defined for conventional petroleum systems.
INTRODUCTION
The Fort Worth Basin in north-central Texas is a foreland basin that formed in respon to the thrusting of the Ouachita structural belt onto the North American continental margin during the Ouachita-Marathon orogeny in the late Mississippian–early Pennsylvanian
AAPG Bulletin,v.91,no.4(April 2007),pp.501–521501
Copyright #2007.The American Association of Petroleum Geologists.All rights rerved.
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Manuscript received June 2,2006;provisional acceptance August 31,2006;revid manuscript received November 22,2006;final acceptance December 6,2006.DOI:10.1306/12060606063
(Flippin,1982;Walper,1982;Grayson et al.,1990).Approximate-ly 0.32billion m 3(2billion bbl)of oil and 0.19trillion m 3(7tcf)of gas have been produced from Ordovician-to Permian-age rer-voirs in the Fort Worth Basin since the early 1900s (Pollastro,2003).The Mississippian Barnett Shale,which averages 4wt.%total or-ganic carbon (TOC),with values as high as 14%in outcrop samples along the Llano uplift (Henk et al.,2000;Jarvie et al.,2001),is the primary petroleum source rock in the basin bad on light hydro-carbon data (Jarvie et al.,2001)and more detailed geochemical analysis (Hill et al.,2007).
Gas shales,and particularly the Barnett Shale,have become some of the most significant onshore exploration targets in the United States,despite extremely low porosity (about 6%)and permeabil-ity (about 0.02md).Initial exploration for gas in the Barnett Shale started in 1982,although it was not until 2000that exploration intensified.Barnett Shale gas yields range from 5300to 7800L/t (170to 250scf/t)bad on corrected methane adsorption data from the Mitchell 2T.P.Sims well and are prent as about 55%free gas and 45%sorbed gas,depending on the interval analyzed within the Barnett Shale (Jarvie et al.,2004).
The organic richness,thermal maturity,gas content,kerogen type,and extent of kerogen transformation are critical for eval-uating shale-gas potential (Jarvie et al.,2004).The data required to complete the appropriate maps for evaluating shale-gas prospects include TOC,Rock-Eval pyrolysis hydrogen index (HI)and T max (temperature at maximum rate of petroleum generation by pyrol-ysis),vitrinite reflectance (R o ),and gas yields.
Integrating petroleum system modeling into the gas-shale pros-pect evaluation process is not routine.The purpo of this article is to demonstrate how kinetic parameters and gas yields derived from pyrolysis experiments can be ud to estimate the gas potential of shales,a potentially valuable tool to further assist in the evaluation of gas-shale prospects,and to establish how shale-gas system
s fit into the petroleum system concept.Geologic Summary
The Fort Worth Basin is an asymmetric,wedge-shape basin con-taining as much as 3700m (12,000ft)of dimentary rocks along the west side of the Muenster arch (Pollastro et al.,2007).This foreland basin formed in front of the advancing Ouachita struc-tural belt as it was thrusted onto the margin of the North America craton during a late Mississippian–early Pennsylvanian episode of plate convergence (Flippin,1982;Walper,1982;Grayson et al.,1990).The Bend arch is a broad,north-plunging,subsurface anticline that extends northward from the Llano uplift (Figure 1)(Pollastro et al.,2007).
The Fort Worth Basin is bounded by the Ouachita structural front to the east and southeast,the Llano uplift to the south,the Bend arch to the west,and the Muenster and Red River arches to the north and northeast (Figure 1).A generalized stratigraphic ction of the
Rearch Center at the California Institute of Technology.Tang has published more than 80articles in the field of geochemistry,chem-istry,and petroleum engineering.His major rearch interests are applying molecular mod-eling and experimental simulation techniques to energy-related problems.He has pioneered the molecular modeling technique to many fields of organic geochemistr
y,surface chem-istry,reaction kinetics,and other petroleum chemistry fields.Tang feels that the major tech-nical barrier of molecular modeling for the pe-troleum industry is the lack of integration be-tween theory and experiments.Thus,his rearch group has a strong integration of modeling and experimental efforts.His main rearch focus are (1)modeling both homogeneous and heterogeneous catalysis;(2)geochemical modeling;(3)interfacial phenomenon model-ing (liquid-liquid,liquid-solid,and gas-solid);(4)nucleation process;(5)emulsion;and (6)ionic liquids.
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ACKNOWLEDGEMENTS
We acknowledge the support of Chevron Pe-troleum Technology Company,Shell Interna-tional Exploration and Production,Inc.,and the U.S.Geological Survey and express our appreciation for their approval to publish the results of our study.We also thank Paul Lillis,J.David King,Peter Warwick,Ken Bird,and Qingming Yang for constructive reviews that significantly improved the article.
502Modeling of Gas Generation from the Barnett Shale
Bend arch–Fort Worth Basin is shown in Figure2.From the Cambrian to the Mississippian,the area that is now the Fort Worth Basin was part of a stable cratonic shelf with deposition dominated by carbonates.The Barnett Shale was deposited over the Ellenburger unconformi-ty during a period of f
oreland basin formation in the late Mississippian,although the Ordovician Viola and Chappell limestones are sometimes prent,and the Simpson is abnt.The formation is prent through-out most of the Fort Worth Basin–Bend arch area and ranges in thickness from a few tens of feet along its western limit to more than305m(1000ft)adjacent to the Muenster arch(Pollastro,2003).Although burial depth is a major factor in Barnett Shale thermal matu-rity,gas generation and conquent gas production are largely controlled by high heat flow related to
Ouachita
Figure1.Generalized
structure map of the Fort
Worth Basin.The lateral
extent of the Barnett Shale
and the U.S.Geological
Survey Fort Worth Basin
boundary are noted.
Modified from Pollastro
et al.(2003).
Hill et al.503
thrusting and fault systems within the Fort Worth Ba-sin (Bowker,2002,2003;Pollastro et al.,2003).The formation is prently in the oil-generation window in the northern and western parts of the basin and in the gas window to the east and south.
EXPERIMENTAL
Two Barnett Shale samples were lected for pyroly-sis,an immature (R o $0.44%),and a mature (R o $1.15%)sample.Geochemical characteristics are sum-marized below.In this study,we have not attempted to characterize gas generation from every facies of the Barnett,but instead have lected two samples that rea-sonably reprent the TOC and Rock-Eval character-istics for the Barnett bad on works of Jarvie et al.(2004).The samples can be ud to compare the gas-generation characteristics of the Barnett at different maturities and can be ud as input into basin mod-eling software to approximate gas generation from the Barnett Shale.
Unpyrolyzed Barnett Shale Samples
玉米烙做法The immature Barnett Shale sample ud in the pyrol-ysis experiments was collected from core from the Chevron 1Moline well,Lampasas County,Texas.The bulk geochemical and maceral data for the shale sample are summarized in Table 1.This sample is relatively immature,with a vitrinite reflectanc
e of 0.44%,TOC of 5.51%,Rock-Eval HI of 346,and an atomic H/C ratio of 1.41.Maceral composition is 93%amorphous,5%vitrinite,1%exinite,and 1%inertinite.
The mature Barnett Shale sample ud in the py-rolysis experiments was collected from core from the Chevron 1St.Clair C well,Erath County,Texas.The bulk geochemical and maceral data for the shale sam-ple are summarized in Table 1.This sample is relatively mature with 1.15%R o ,TOC of 4.51%,Rock-Eval HI of 68,and 1.06H/C atomic ratio.Maceral composition is 91%amorphous,3%vitrinite,1%exinite,and 5%inertinite.
Clod-System Pyrolysis
Sealed gold-tube pyrolysis experiments were per-formed on the immature Barnett Shale kerogen isolate under elevated pressure and two heating rate
conditions
四条包子Figure 2.Generalized stratigraphic ction for the Fort Worth Basin showing the Barnett Shale in relation to other stratigraphic units.Modified from Pollastro et al.(2003).504
Modeling of Gas Generation from the Barnett Shale
following the methods of Tang et al.(1996)and Zhang et al.(2007).The experiments allowed us to accurate-ly monitor the changes in gas yield,gas molecular com-position,vitrinite reflectance(R o),and elemental com-position of the residual shale samples.Bad on the pyrolysis data and using the Lawrence Livermore Na-tional Lab Kinetics software,ts of specific kinetic models were derived for R o change and gas generation.
Pyrolysis experiments were performed using aled gold tubes(50mm[1.9in.]length,3.6mm[0.14in.] inner diameter,and0.4mm[0.015in.]wall thickness) in a high-pressure and high-temperature pyrolysis sys-tem(Hill et al.,1994,1996;Zhang et al.,2007).The clean tubes were welded at one end before sample load-ing.About100mg of vacuum-dried,finely powdered, and homogenized kerogen isolate sample was loaded into each gold tube in a glove box containing an argon atmosphere.The tubes were flushed with argon in the box for15min to ensure the complete removal of air. The other end of the gold tube was then welded under an argon atmosphere using the methods of Hill et al. (1994,1996).
策划书范文案例The aled gold tubes were put into stainless-steel vesls that were then placed in a large oven and kept at a constant pressure of5000psi(34.5MPa)during the cour of the experiment.Water was the pressure me-dium and was controlled by an air-driven pump.The samples were heated using tw
o different nonisothermal heating programs of10j C/hr from150to469j C and 1j C/hr from150to456j C,respectively.The temper-ature was controlled using the oven’s built-in PRO-SET temperature controller and measured directly(accura-cy±1j C)with two thermocouples fixed on the top and bottom of each vesl,recorded,and stored on a com-puter.A vesl containing gold tubes was removed from the oven at temperature intervals of20–30j C between 280j C and the final temperature.Each vesl was quickly cooled to room temperature and then depressurized slowly before the gold tubes were unloaded from the vesls.
Pyrolysis Product Analysis
Pyrolysis products were analyzed for gas yield,molecu-lar composition,and residual vitrinite reflectance(R o). Hill et al.(1994,1996)previously summarized the analytical methods and reproducibility.Briefly,the gold tube was pierced in the vacuum line with a needle, allowing the gas to escape into the line and the liquid products(C6+fractions)to be trapped into a dry ice-acetone trap(T=À77j C).The remaining gas were collected by a Toepler pump into a calibrated volume for total fraction quantification and then introduced directly into a gas chromatograph(GC)for composi-tion analysis.The molecular quantification of both hy-drocarbon and nonhydrocarbon gas was performed on a two-channel Hewlett Packard6890ries GC that was custom configured by Wasson
ECE Instrumenta-tion with two capillary and four packed columns,in conjunction with a flame ionization detector(FID)and two thermal conductivity detectors(TCD).
The C1–C5hydrocarbons were analyzed on chan-nel A of the GC using helium as a carrier gas,two
Table1.Maceral Composition and Geochemical Parameters
for Barnett Shale Samples
Sample Immature Mature
Vitrinite reflectance(%)0.44 1.15
Maceral composition
致命交叉点
Amorphous(%)9391
课题研究总体框架
Exinite(%)11
Vitrinite(%)53
Inertinite(%)15
Rock-Eval and total organic carbon*
TOC(%) 5.51 4.51
S1(mg HC/g rock) 2.39 1.73
S2(mg HC/g rock)19.1 3.07
S3(mg CO2/g rock) 1.080.23
T max(j C)441463
HI(mg HC/g TOC)34668
OI(mg CO2/g TOC)205
PI0.120.36
S2/S317.6813.35
Elemental composition
Carbon32.5622.78
Hydrogen 3.79 2.02
Oxygen 4.39 4.7
Sulfur9.9N.D.**
Nitrogen<0.01N.D.
H/C 1.41 1.06
O/C0.10.15
*S1=thermally extractable petroleum;S2=petroleum generated by pyrolysis;
S3=carbon dioxide generated by pyrolysis;T max=temperature at which
S2generation rate is maximum;HI=hydrogen index(S2/TOCÂ100);OI=
oxygen index(S3/TOCÂ100);PI=production index(S1/(S1+S2)).
**N.D.=not determined.
Hill et al.505
