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Basin-centered gas systems: development (view source)
Revision as of 22:00, 13 January 2015
, 22:00, 13 January 2015no edit summary
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The developmental history of a basin-centered gas system (BCGS) may be viewed as four reservoir pressure cycles. As a consequence of the dynamic nature of geologic processes and the response to those processes, the phases discussed here are geologically ephemeral. [[:file:BasinCenteredGasFig1.jpg|Figure 1]] is a diagrammatic representation showing these pressure phases and the development of direct and indirect BCGSs. Meissner<ref name=Meissner_1978>Meissner, F. Fm 1978, Patterns of source-rock maturity in non-marine source rocks of some typical western interior basins in non-marine Tertiary and Upper Cretaceous source rocks and the occurrence of oil and gas in the west central U.S.:Roky Mountain Association of Geologists Continuing Education Notes, unpaginated.</ref> and Law and Dickinson<ref name=Lawanddickinson_1985>Law, B. E., and W. W. Dickinson, 1985, [http://archives.datapages.com/data/bulletns/1984-85/data/pg/0069/0008/1250/1295.htm A conceptual model for the origin of abnormally pressured gas accumulations in low-permeability reservoirs]: AAPG Bulletin, v. 69, p. 1295-1304.</ref> discussed these phase changes for gas accumulations in low-permeability reservoirs.
The developmental history of a basin-centered gas system (BCGS) may be viewed as four reservoir pressure cycles. As a consequence of the dynamic nature of geologic processes and the response to those processes, the phases discussed here are geologically ephemeral. [[:file:BasinCenteredGasFig1.jpg|Figure 1]] is a diagrammatic representation showing these pressure phases and the development of direct and indirect BCGSs. Meissner<ref name=Meissner_1978>Meissner, F. Fm 1978, Patterns of source-rock maturity in non-marine source rocks of some typical western interior basins in non-marine Tertiary and Upper [[Cretaceous]] source rocks and the occurrence of oil and gas in the west central U.S.:Roky Mountain Association of Geologists Continuing Education Notes, unpaginated.</ref> and Law and Dickinson<ref name=Lawanddickinson_1985>Law, B. E., and W. W. Dickinson, 1985, [http://archives.datapages.com/data/bulletns/1984-85/data/pg/0069/0008/1250/1295.htm A conceptual model for the origin of abnormally pressured gas accumulations in low-permeability reservoirs]: AAPG Bulletin, v. 69, p. 1295-1304.</ref> discussed these phase changes for gas accumulations in low-permeability reservoirs.
[[file:BasinCenteredGasFig1.jpg|thumb|400px|{{figure number|1}}Schematic diagram showing evolution of direct and indirect basin-centered gas systems. Evolutionary phases are shown along the side of each system.]]
[[file:BasinCenteredGasFig1.jpg|thumb|400px|{{figure number|1}}Schematic diagram showing evolution of direct and indirect basin-centered gas systems. Evolutionary phases are shown along the side of each system.]]
==Phase II==
==Phase II==
===Direct systems===
===Direct systems===
Direct systems require gas-prone source rocks and low-permeability reservoirs in close proximity to each other. As the source and reservoir rocks undergo further burial and exposure to increasing temperatures, the source rocks begin to generate gas ([[:file:BasinCenteredGasFig1.jpg|Figure 1]]). Concomitant with increased gas generation, expulsion, and migration, gas begins to enter adjacent, water-wet sandstones. Because these sandstones have low permeability, the rate at which gas is generated and accumulated in reservoirs is greater than the rate at which gas is lost. Eventually, as newly generated gas accumulates in the pore system, the capillary pressure of the water-wet pores is exceeded, and free, mobile water is expelled from the pore system, resulting in the development of an overpressured, gas-saturated reservoir with little or no free water. Examples of BCGA systems exhibiting this overpressured phase include the Greater Green River,<ref name=Law_1984 /> Wind River,<ref name=Johnsonetal_1996 /> Big Horn,<ref name=Johnsonetal_1999 /> and Piceance basins<ref name=Johnsonetal_1987 /> in the Rocky Mountain region of the United States and the Taranaki Basin in New Zealand (B. E. Law, 2000, unpublished data) (Table 1).
Direct systems require gas-prone source rocks and low-permeability reservoirs in close proximity to each other. As the source and reservoir rocks undergo further burial and exposure to increasing temperatures, the source rocks begin to generate gas ([[:file:BasinCenteredGasFig1.jpg|Figure 1]]). Concomitant with increased gas generation, expulsion, and migration, gas begins to enter adjacent, water-wet sandstones. Because these sandstones have low permeability, the rate at which gas is generated and accumulated in reservoirs is greater than the rate at which gas is lost. Eventually, as newly generated gas accumulates in the pore system, the capillary pressure of the water-wet pores is exceeded, and free, mobile water is expelled from the pore system, resulting in the development of an overpressured, gas-saturated reservoir with little or no free water. Examples of BCGA systems exhibiting this overpressured phase include the Greater Green River,<ref name=Law_1984>Law, B. E., 1984, Relationships of source rocks, thermal maturity, and overpressuring to gas generation and occurrence in low-permeability Upper Cretaceous and lower Tertiary rocks, Greater Green River basin, Wyoming, Colorado, and Utah, ''in'' J. Woodward, F. F. Meissner, and J. L. Clayton, eds., Hydrocarbon source rocks of the greater Rocky Mountain region: Rocky Mountain Association of Geologists Guidebook, P. 469-490.</ref> Wind River,<ref name=Johnsonetal_1996>Johnson, R. C., T. M. Finn, R. A. Crovelli, and R. H. Balay, 1996, [http://pubs.er.usgs.gov/publication/ofr96264 An assessment of in-place gas resources in low-permeability Upper Cretaceous and lower Tertiary sandstone reservoirs, Wind River basin, Wyoming]: U.S. Geological Survey Open-File Report 96-264, 67 p.</ref> Big Horn,<ref name=Johnsonetal_1999>Johnson, R. C., R. A. Crovelli, B. G. Lowell, and T. M. Finn, 1999, [http://pubs.er.usgs.gov/publication/ofr99315A An assessment of in-place gas resources in the low-permeability basin-centered gas accumulation of the Big Horn basin, Wyoming and Montana]: U.S. Geological Survey Open-File Report 99-315A, 123 p.</ref> and Piceance basins<ref name=Johnsonetal_1987>Johnson, R. C., R. A. Crovelli, C. W. Spencer, and R. F. Mast, 1987, [http://pubs.er.usgs.gov/publication/ofr87357 An assessment of gas resources in low-permeability sandstones of the Upper Cretaceous Mesaverde Group, Piceance basin, Colorado]: U.S. Geological Survey Open-File Report 87-357, 165 p.</ref> in the Rocky Mountain region of the United States and the Taranaki Basin in New Zealand (B. E. Law, 2000, unpublished data) (Table 1).
{| class = "wikitable"
{| class = "wikitable"
| colspan=5 | <div style="text-align: center;">'''NORTH AMERICA'''</div>
| colspan=5 | <div style="text-align: center;">'''NORTH AMERICA'''</div>
|-
|-
| Colville basin, Alaska || High || Cretaceous || Direct ? || Popov et al.<ref name=Popovetal_2001 />
| Colville basin, Alaska || High || Cretaceous || Direct ? || Popov et al.<ref name=Popovetal_2001>Popov, M. A., V. F. Nuccio, T. S. Dyman, T. A. Gognat, R. C. Johnson, J. W. Schmoker, M. S. Wilson, and C. Bartberger, 2001, Basin-centered gas systems of the U.S.:U.S. Geological Survey Open-File Report 01-135, Version 1.0, 1 CD-ROM.</ref>
|-
|-
| Central Alaska basins || Low/Moderate || ? || ? || Popov et al.<ref name=Popovetal_2001 />
| Central Alaska basins || Low/Moderate || ? || ? || Popov et al.<ref name=Popovetal_2001 />
| Cook Inlet, Alaska || Low || pre-Tertiary || ? || Popov et al.<ref name=Popovetal_2001 />
| Cook Inlet, Alaska || Low || pre-Tertiary || ? || Popov et al.<ref name=Popovetal_2001 />
|-
|-
| Norton Basin, Alaska || High || Eocene/Paleocene || Direct || Smith<ref name=Smith_1994 />
| Norton Basin, Alaska || High || [[Eocene]]/[[Paleocene]] || Direct || Smith<ref name=Smith_1994>Smith, J. T., 1994, [http://archives.datapages.com/data/specpubs/methodo2/data/a077/a077/0001/0000/0025.htm Petroleum system logic as an exploration tool in a frontier setting], ''in'' L. B. Magoon and W. G. Dow, eds., The petroleum system-from source to trap: AAPG Memoir 60, p. 25-49.</ref>
|-
|-
| Alberta basin, Canada || High || Cretaceous || Direct || Masters<ref name=Masters_1979 /><ref name=Masters_1984 />
| Alberta basin, Canada || High || Cretaceous || Direct || Masters<ref name=Masters_1979>Masters, J. A., 1979, [http://archives.datapages.com/data/bulletns/1977-79/data/pg/0063/0002/0150/0152.htm Deep basin gas trap, western Canada]: AAPG Bulletin, v. 63, p. 152-181.</ref> <ref name=Masters_1984>Masters, J. A., ed., 1984, [http://archives.datapages.com/data/alt-browse/aapg-special-volumes/m38.htm Elmworth-case study of a deep basin gas field]: AAPG Memoir 38, 316 p.</ref>
|-
|-
| Charlotte-Georgia Basin, Canada || Low/Moderate || Tertiary/Cretaceous || Direct ? ||
| Charlotte-Georgia Basin, Canada || Low/Moderate || Tertiary/Cretaceous || Direct ? ||
|-
|-
| Willamette-Puget Sound Trough, Washington and Oregon || Moderate/High || Tertiary || Direct ? || Law,<ref name=Law_1996 /> Popov et al.<ref name=Popovetal_2001 />
| Willamette-Puget Sound Trough, Washington and Oregon || Moderate/High || Tertiary || Direct ? || Law,<ref name=Law_1996>Law, B. E., 1996, Southwestern Wyoming province (037), ''in'' D. L. Gautier, G. L. Dolton, K. I. Takahashi, and K. L. Varnes, eds., [http://pubs.usgs.gov/dds/dds-030/ 1995 national assessment of United States oil and gas resources-results, methodology, and supporting data]: U.S. Geological Survey Digital Data Series DDS-30, Release 2, 1 CD-ROM.</ref> Popov et al.<ref name=Popovetal_2001 />
|-
|-
| Columbia basin, Washington || High || Tertiary || Direct || Law et al.,<ref name=Lawetal_1994 /> Law<ref name=Law_1996 />
| Columbia basin, Washington || High || Tertiary || Direct || Law et al.,<ref name=Lawetal_1994>Law, B. E., M. E. Tennyson, and S. Y. Johnson 1994, Basin-centered gas accumulations in the Pacific Northwest-a potentially large source of energy (abs.): AAPG Annual Meeting Program, v. 3, p. 194.</ref> Law<ref name=Law_1996 />
|-
|-
| Modoc Plateau, California || Low/Moderate || Cretaceous || Direct ? || Popov et al.<ref name=Popovetal_2001 />
| Modoc Plateau, California || Low/Moderate || Cretaceous || Direct ? || Popov et al.<ref name=Popovetal_2001 />
| Wind River basn, Wyoming || High || Cretaceous || Direct || Johnson et al.<ref name=Johnsonetal_1996 />
| Wind River basn, Wyoming || High || Cretaceous || Direct || Johnson et al.<ref name=Johnsonetal_1996 />
|-
|-
| Greater Green River basin, Wyoming || High || Lower Tertiary/Cretaceous || Direct || Law et al.,<ref name=Lawetal_1979 /> Law et al.,<ref name=Lawetal_1980 /> McPeek,<ref name=Mcpeek_1981 /> Law,<ref name=Law_1984 /> Law et al.<ref name=Lawetal_1989 />
| Greater Green River basin, Wyoming || High || Lower Tertiary/Cretaceous || Direct || Law et al.,<ref name=Lawetal_1979>Law, B. E., C. W. Spencer, and N. H. Bostic, 1979, Preliminary results of organic maturation, temperature, and pressure studies in the Pacific Creek area, Sublette County, Wyoming, ''in'' 5th Department of Energy symposium on enhanced oil and gas recovery and improved drilling methods, v. 3-oil and gas recovery: Tulsa, Oklahoma, Petroleum Publishing, p. K-2/1-K-2/13.</ref> Law et al.,<ref name=Lawetal_1980>Law, B. E., C. W. Spencer, and N. H. Bostick, 1980, Evaluation of organic maturation, subsurface temperature, and pressure with regard to gas generation in low-permeability Upper Cretaceous and lower Tertiary strata in the Pacific Creek area, Sublette County, Wyoming: Mountain Geologist, v. 17, no. 2, p. 23-35.</ref> McPeek,<ref name=Mcpeek_1981>McPeek, L. A., 1981, [http://archives.datapages.com/data/bulletns/1980-81/data/pg/0065/0006/1050/1078.htm Eastern Green River basin-a developing giant gas supply from deep, overpressured Upper Cretaceous sandstones]: AAPG Bulletin, v. 65, p. 1978-1098.</ref> Law,<ref name=Law_1984 /> Law et al.<ref name=Lawetal_1989>Law, B. E., C. W. Spencer, R. R. Charpentier, R. A. Crovelli, R. F. Mast, G. L. Dolton, and C. J. Wandrey, 1989, Estimates of gas resources in overpressured low-permeability Cretaceous and Tertiary sandstone reservoirs, Greater Green River basin, Wyoming, Colorado, and Utah: 40th Annual Field Conference, Wyoming Geological Association Guidebook, p. 39-61.</ref>
|-
|-
| Hanna basin, Wyoming || High || Cretaceous || Direct || Popov et al.,<ref name=Popovetal_2001 /> Wilson et al.<ref name=Wilsonetal_2001 />
| Hanna basin, Wyoming || High || Cretaceous || Direct || Popov et al.,<ref name=Popovetal_2001 /> Wilson et al.<ref name=Wilsonetal_2001>Wilson, M. S., T. S. Dyman, and V. F. Nuccio, 2001, [http://pubs.usgs.gov/bul/b2184-a/ Potential for deep basin-centered gas accumulations in Hanna basin, Wyoming]: U.S. Geological Survey Bulletin 2184-A, 12 p.</ref>
|-
|-
| Powder River basin, Wyoming || High || Cretaceous || ? || Surdam et al.,<ref name=Surdametal_1994 /> Maucione et al.<ref name=Maucioneetal_1994 />
| Powder River basin, Wyoming || High || Cretaceous || ? || Surdam et al.,<ref name=Surdametal_1994>Surdam, R. C., Z. S. Jiao, and R. S. Martinsen, 1994, [http://archives.datapages.com/data/specpubs/memoir61/ch15/0213.htm The regional pressure regime in Cretaceous sandstones and shales in the Powder River basin], ''in'' P. J. Ortoleva, ed., Basin compartments and seals: AAPG Memoir 61, p. 213-233.</ref> Maucione et al.<ref name=Maucioneetal_1994>Maucion, D., V. Serebryakov, P. Valasek, Y. Wang, and S. Smithson, 1994, [http://archives.datapages.com/data/specpubs/memoir61/ch22/0333.htm A sonic log study of abnormally pressured zones in the Powder River basin of Wyoming], ''in'' P. J. Ortoleva, ed., Basin compartments and seals: AAPG Memoir 61, p. 333-348.</ref>
|-
|-
| Wasatch Plateau, Utah || Moderate/High || Cretaceous || Direct || Popov et al.<ref name=Popovetal_2001 />
| Wasatch Plateau, Utah || Moderate/High || Cretaceous || Direct || Popov et al.<ref name=Popovetal_2001 />
|-
|-
| Uinta basin, Utah || High || Lower Tertiary/Cretaceous || Direct || Fouch et al.,<ref name=Fouchetal_1992 /> Fouch and Schmoker,<ref name=Fouchandschmoker_1996 /> Popov et al.<ref name=Popovetal_2001 />
| Uinta basin, Utah || High || Lower [[Tertiary]]/Cretaceous || Direct || Fouch et al.,<ref name=Fouchetal_1992>Fouch, T. D., V. F. Nuccio, J. C. Osmond, L. MacMillan, W. B. Cachion, and C. J. Wandrey, 1992, Oil and gas in uppermost Cretaceous and Tertiary rock, Uinta basin, Utah, ''in'' T. D. Fouch, V. F. Nuccio, and T. C. Chidsey Jr., eds., Hydrocarbon and mineral resources of the Uinta basin, Utah and Colorado: Utah Geological Association Guidebook 20, p. 9-47.</ref> Fouch and Schmoker,<ref name=Fouchandschmoker_1996>Fouch, T. D., and J. W. Schmoker, 1996, Tight gas plays of the Uinta basin, ''in'' D. L. Gautier, G. L. Dolton, K. I. Takahashi, and K. L. Varnes, eds, [http://pubs.usgs.gov/dds/dds-030/ 1995 national assessment of United States oil and gas resources-results, methodology, and supporting data]: U.S. Geological Survey Digital Data Series DDS-30, Release 2, 1 CD-ROM.</ref> Popov et al.<ref name=Popovetal_2001 />
|-
|-
| Piceance basin, Colorado || High || Cretaceous || Direct || Johnson et al.,<ref name=Johnsonetal_1987 /> Spencer,<ref name=Spencer_1987 /> Spencer<ref name=Spencer_1989a />
| Piceance basin, Colorado || High || Cretaceous || Direct || Johnson et al.,<ref name=Johnsonetal_1987 /> Spencer,<ref name=Spencer_1987>Spencer, C. W., 1987, [http://archives.datapages.com/data/bulletns/1986-87/data/pg/0071/0004/0350/0368.htm Hydrocarbon generation as a mechanism for overpressuring in Rocky Mountain region]: AAPG Bulletin, v. 71, p. 368-388.</ref> Spencer<ref name=Spencer_1989a>Spencer, C. W., 1989, [http://archives.datapages.com/data/bulletns/1988-89/data/pg/0073/0005/0600/0613.htm Review of characteristics of low-permeability gas reservoirs in western United States]: AAPG Bulletin, v. 73, p. 613-629.</ref>
|-
|-
| South Park basin, Colorado || Moderate/High || Cretaceous || Direct/Indirect || Popov et al.<ref name=Popovetal_2001 />
| South Park basin, Colorado || Moderate/High || Cretaceous || Direct/Indirect || Popov et al.<ref name=Popovetal_2001 />
|-
|-
| Raton basin, New Mexico and Colorado || High || Tertiary/Cretaceous || Direct/Indirect || Johnson and Finn,<ref name=Johnsonandfinn_2001 /> Popov et al.<ref name=Popovetal_2001 />
| Raton basin, New Mexico and Colorado || High || Tertiary/Cretaceous || Direct/Indirect || Johnson and Finn,<ref name=Johnsonandfinn_2001>Johnson, R. C., and T. M. Finn, 2001, [http://pubs.usgs.gov/bul/b2184-b/ Potential for basin-centered gas accumulation in the Raton basin, Colorado and New Mexico]: U.S. Geological Survey Bulletin 2184-B, 14 p.</ref> Popov et al.<ref name=Popovetal_2001 />
|-
|-
| Denver basin, Colorado || High || Cretaceous || Direct/Indirect || Higley et al.,<ref name=Higleyetal_1992 /> Popov et al.<ref name=Popovetal_2001 />
| Denver basin, Colorado || High || Cretaceous || Direct/Indirect || Higley et al.,<ref name=Higleyetal_1992>Higley, D. K., D. L. Gautier, and M. J. Pawlewicz, 1992, Influence of regional head flow variation on thermal maturity of the Lower Cretaceous Muddy ("J") Sandstone, Denver basin, Colorado, ''in'' [http://pubs.usgs.gov/bul/2007/report.pdf The petroleum system-status of research and methods, 1992]: U.S. Geological Survey Bulletin 2007, p. 66-69.</ref> Popov et al.<ref name=Popovetal_2001 />
|-
|-
| San Juan basin, New Mexico and Colorado || High || Cretaceous || Direct || Silver,<ref name=Silver_1950 /> Masters,<ref name=Masters_1979 /> Huffman<ref name=Huffman_1996 />
| San Juan basin, New Mexico and Colorado || High || Cretaceous || Direct || Silver,<ref name=Silver_1950>Silver, C., 1950, The occurrence of gas in the Cretaceous rocks of the San Juan basin, New Mexico and Colorado: New Mexico Geological Society, First Field Conference, San Juan basin, p. 109-123.</ref> Masters,<ref name=Masters_1979 /> Huffman<ref name=Huffman_1996>Huffman, A. C., 1996, San Juan basin province, ''in'' D. L. Gautier, G. L. Dolton, K. I. Takahashi, and K. L. Varnes, eds, [http://pubs.usgs.gov/dds/dds-030/ 1995 national assessment of United States oil and gas resources-results, methodology, and supporting data]: U.S. Geological Survey Digital Data Series DDS-30, Release 2, 1 CD-ROM.</ref>
|-
|-
| Permian basin, New Mexico || High || Permian || Indirect/Direct || Broadhead,<ref name=Broadhead_1984 /> Popov et al.<ref name=Popovetal_2001 />
| Permian basin, New Mexico || High || [[Permian]] || Indirect/Direct || Broadhead,<ref name=Broadhead_1984>Broadhead, R. F., 1984, Geology of gas production from tight Abo red beds, east central New Mexico: Oil & Gas Journal, v. 82, no. 24, p. 147-158.</ref> Popov et al.<ref name=Popovetal_2001 />
|-
|-
| Albuquerque basin, New Mexico || Moderate/High || Cretaceous || Direct || Johnson et al.<ref name=Johnsonetal_2001 /> Popov et al.<ref name=Popovetal_2001 />
| Albuquerque basin, New Mexico || Moderate/High || Cretaceous || Direct || Johnson et al.<ref name=Johnsonetal_2001>Johnson, R. C., T. M. Finn, and V. F. Nuccio, 2001, [http://pubs.usgs.gov/bul/b2184-c/ Potential for basin-centered gas accumulation in the Albuquerque basin, New Mexico]: U.S. Geological Survey Bulletin 2184-C, 21 p.</ref> Popov et al.<ref name=Popovetal_2001 />
|-
|-
| Anadarko basin, Oklahoma || High || Pennsylvanian || Indirect || Al-Shaieb et al.,<ref name=Alshaiebetal_1994 /> Popov et al.<ref name=Popovetal_2001 />
| Anadarko basin, Oklahoma || High || [[Pennsylvanian]] || Indirect || Al-Shaieb et al.,<ref name=Alshaiebetal_1994>Al-Shaieb, Z., J. Puckette, A. Abdalla, and P. B. Ely, 1994, [http://archives.datapages.com/data/specpubs/memoir61/ch04/0055.htm Megacompartment complex in the Anadarko basin: A completely sealed overpressured phenomenon], ''in'' P. J. Ortoleva, ed., Basin compartments and seals: AAPG Memoir 61, p. 55-62.</ref> Popov et al.<ref name=Popovetal_2001 />
|-
|-
| Midcontinent Rift, Minnesota and Iowa || Low/Moderate || Precambrian || Indirect/Direct || Popov et al.<ref name=Popovetal_2001 />
| Midcontinent Rift, Minnesota and Iowa || Low/Moderate || [[Precambrian]] || Indirect/Direct || Popov et al.<ref name=Popovetal_2001 />
|-
|-
| Arkoma basin, Arkansas and Oklahoma || High || Pennsylvanian || Direct || Meckel et al.,<ref name=Meckeletal_1992 /> Popov et al.<ref name=Popovetal_2001 />
| Arkoma basin, Arkansas and Oklahoma || High || Pennsylvanian || Direct || Meckel et al.,<ref name=Meckeletal_1992>Meckel, L. D., D. G. Smith, and L. A. Wells, 1992, [http://archives.datapages.com/data/specpubs/basinar3/data/a136/a136/0001/0400/0427.htm Ouachita foredeep basins: Regional paleogeography and habitat of hydrocarbons], ''in'' R. W. Macqueen and D. A. Leckie, eds., Foreland basins and fold belts: AAPG Memoir 55, p. 427-444.</ref> Popov et al.<ref name=Popovetal_2001 />
|-
|-
| Gulf Coast, United States || High || Cretaceous || Indirect || Popov et al.<ref name=Popovetal_2001 />
| Gulf Coast, United States || High || Cretaceous || Indirect || Popov et al.<ref name=Popovetal_2001 />
|-
|-
| East Texas basin, Texas || High || Jurassic || Indirect ? || Montgomery and Karlewiz,<ref name=Montgomeryandkarlewicz_2001 /> Emme and Stancil<ref name=Emmeandstancil_2002 />
| East Texas basin, Texas || High || [[Jurassic]] || Indirect ? || Montgomery and Karlewiz,<ref name=Montgomeryandkarlewicz_2001>Montgomery, S. L., and R. Karlewicz, 2001, Bossier play has room to grow: Oil & Gas Journal, v. 99, no. 5, p. 36-42.</ref> Emme and Stancil<ref name=Emmeandstancil_2002>Emme, J., and B. Stancil, 2002, Anadarko's Bossier gas play-a sleeping giant in a mature basin (abs.): AAPG Annual Meeting Program, v. 11, p. A50.</ref>
|-
|-
| Black Warrior basin, Alabama and Mississippi || Moderate/High || Pennsylvanian || Direct || Popov et al.<ref name=Popovetal_2001 />
| Black Warrior basin, Alabama and Mississippi || Moderate/High || Pennsylvanian || Direct || Popov et al.<ref name=Popovetal_2001 />
|-
|-
| Michigan basin, Michigan || Low/Moderate || Ordovician || ? || Popov et al.<ref name=Popovetal_2001 />
| Michigan basin, Michigan || Low/Moderate || [[Ordovician]] || ? || Popov et al.<ref name=Popovetal_2001 />
|-
|-
| Appalachian basin, eastern United States || High || Silurian/Devonian || Indirect || Davis,<ref name=Davis_1984 /> Law and Spencer,<ref name=Lawandspencer_1993 /> Law and Spencer,<ref name=Lawandspencer_1998 /> Popov et al.,<ref name=Popovetal_2001 /> Ryder and Zagorski<ref name=Ryderandzagorski_2003>Ryder, R. T., and W. A. Zagorski, 2003, [http://archives.datapages.com/data/bulletns/2003/05may/0847/0847.HTM Nature, origin, and production characteristics of the Lower Silurian regional oil and gas accumulation, central Appalachian basin, United States]: AAPG Bulletin, v. 87, no. 5, p. 847-872.</ref>
| Appalachian basin, eastern United States || High || [[Silurian]]/[[Devonian]] || Indirect || Davis,<ref name=Davis_1984>Davis, T. B., 1984, [http://archives.datapages.com/data/specpubs/fieldst4/data/a013/a013/0001/0150/0189.htm Subsurface pressure profiles in gas saturated basins], ''in'' J. A. Masters, ed., Elmworth-case study of a deep basin gas field: AAPG Memoir 38, p. 189-203.</ref> Law and Spencer,<ref name=Lawandspencer_1993>Law, B. E., and C. W. Spencer, 1993, Gas in tight reservoirs-an emerging source of energy, ''in'' D. G. Howell, ed., The future of energy gases: [http://pubs.er.usgs.gov/publication/pp1570 U.S. Geological Survey Professional Paper 1570], p. 233-252.</ref> Law and Spencer,<ref name=Lawandspencer_1998 /> Popov et al.,<ref name=Popovetal_2001 /> Ryder and Zagorski<ref name=Ryderandzagorski_2003>Ryder, R. T., and W. A. Zagorski, 2003, [http://archives.datapages.com/data/bulletns/2003/05may/0847/0847.HTM Nature, origin, and production characteristics of the Lower Silurian regional oil and gas accumulation, central Appalachian basin, United States]: AAPG Bulletin, v. 87, no. 5, p. 847-872.</ref>
|-
|-
| colspan=5 | <div style="text-align: center;">'''SOUTH AMERICA'''</div>
| colspan=5 | <div style="text-align: center;">'''SOUTH AMERICA'''</div>
|-
|-
|ASDF
|Chaco basin, Bolivia || Moderate || Devonian || ? || Williams et al.<ref name=Williamsetal_1995>Williams, K. E., B. J. Radovich, and J. W. Brett, 1995, Exploration for deep gas in the Devonian Chaco basin of southern Bolivia: Sequence stratigraphy, prediction, and well results (abs.): AAPG Annual Convention, Abstracts with Program, v. 4, p. A104.</ref>
|-
| Neuquen basin, Argentina || High || ? || ? || Fernandez-Sevesco and Surdam<ref name=Fernandezsevescoandsurdam_1997>Fernandez-Sevesco, F., and R. C. Surdam, 1997, A new exploration approach in the search for anomalously pressured hydrocarbon accumulations in the Neuquen Basin, Argentina (abs.): AAPG International Conference and Exhibition Program, p. A16.</ref>
|-
| colspan=5 | <div style="text-align: center;">'''EUROPE'''</div>
|-
| Timan-Pechora basin, Russa || High || Permian || Direct || Law et al.<ref name=Lawetal_1996>Law, B. E., V. I. Bogatsky, S. . Danilevsky, L. V. Galkina, G. F. Ulmishek, and C. W. Spencer, 1996, Basin-centered gas accumulations in the Timan-Pechora basin, Russia (abs.): AAPG Annual Convention Program, v. 5, p. A81.</ref>
|-
| Dnieper-Donets basin, Ukraine || High || [[Carboniferous]] || Direct || Law et al.<ref name=Lawetal_1998b>Law, B. E., G. F. Ulmishek, B. P. Kabyshev, N. T. Pashova, and V. A. Krivosheya, 1998, Basin-centered gas evaluated in Dnieper-Donets basin, Donbas foldbelt, Ukraine: Oil & Gas Journal, v. 100, no. 30, p. 74-78.</ref>
|-
| West Netherlands basin, Netherlands || Indeterminate || ? || ? ||
|-
| Vlieland basin, Netherlands || Indeterminate || ? || ? ||
|-
| Polish basin, Poland || Indeterminate || ? || ? ||
|-
| Upper Silesian basin, Poland || Indeterminate || ? || ? ||
|-
| Bekes basin, Hungary || Moderate/High || Miocene || ? || Spencer et al.<ref name=Spenceretal_1994 />
|-
| German basin, Germany || Indeterminate || ? || ? ||
|-
| Ruhr basin, Germany || Indeterminate || ? || ? ||
|-
| Thuringian basin, Germany || Indeterminate || ? || ? ||
|-
| Subhercynian basin, Germany || Indeterminate || ? || ? ||
|-
| Lower Saxony basin, Germany || Indeterminate || ? || ? ||
|-
| Saar-Nahe basin, Germany and France || Indeterminate || ? || ? ||
|-
| Rhine graben, Germany and France || Indeterminate || ? || ? ||
|-
| Nord-pas-de-Calais basin, France || Indeterminate || ? || ? ||
|-
| Lorraine basin, France || Indeterminate || ? || ? ||
|-
| Bresse basin, France || Indeterminate || ? || ? ||
|-
| Southeast basin, France || Indeterminate || ? || ? ||
|-
| Vienna basin, Austria and Slovakia || Indeterminate || ? || ? ||
|-
| Alpine Foreland basin, Switzerland || High || Permian/Carboniferous || Direct || Schegg et al.<ref name=Scheggetal_1997>Schegge, R., W. Leu, and E. Greber, 1997, New exploration concepts spark Swiss gas, oil prospects: Oil & Gas Journal, v. 95, no. 39, p. 102-106.</ref>
|-
| colspan=5 | <div style="text-align: center;">'''ASIA-PACIFIC'''</div>
|-
| Sichuan basin, China || High || Permian/[[Triassic]] || Direct ? || Da-jun and Yun-ho,<ref name=Dajunandyunho_1994>Da-jun, P., and L. Yun-ho, 1994, Genetic mechanism of abnormal pressure, pressure seals, and natural gas accumulation in carbonate reservoirs, Sichuan basin: Proceedings of the AAPG Research Conference Abnormal Pressures in Hydrocarbon Environments, unpaginated.</ref> Ryder et al.<ref name=Ryderetal_1994>Ryder, R. T., D. D. Rice, Z. Sun, Y. Zhanz, Y. Qui, and Z. Guo, 1994, Petroleum geology of the Sichuan basin China-report on U.S. Geological Survey and Chinese Ministry of Geology and Mineral Resources, field investigation and meeting, October 1991: U.S. Geological Survey Open-File Report 94-426, 67 p.</ref>
|-
| Ordos Basin, China || High || Permian || ? ||
|-
| Jungar basin, China || High || Permian || ? || Zha et al.<ref name=Zhaetal_1999>Zha, M., W. Zhang, and Q. Jiangxiu, 1999, Overpressured compartments in Junggar basin, northwest of China: Mechanisms and hydrocarbon distribution (abs.): AAPG Annual Convention, Program with Abstracts, v. 8, p. A158-159.</ref>
|-
| Taranaki Basin, New Zealand || High || Eocene || Direct ||
|-
| Gippsland Basin, Australia || Moderate || Lower Tertiary/Cretaceous || Direct || Stainforth<ref name=Stainforth_1984>Stainforth, J.G., 1984, Gippsland hydrocarbons-a perspective from the basin edge: Australian Petroleum Exploration Association Journal, v. 24, p. 91-100.</ref>
|-
| Barrow Subbasin, Australia || High || Jurassic || ? || He and Middleton<ref name=Heandmiddleton_2002>He, S., and M. Middleton, 2002, Pressure seal and modeling of the Jurassic overpressure in the Barrow Sub-basin, northwest shelf of Australia (abs.): AAPG Annual Meeting Program, v. 11, p. A74.</ref>
|-
| Perth basin (onshore), Australia || Moderate || Jurassic || ? || Crostella<ref name=Crostella_1995a>Crostella, A., 1995, An evaluation of the hydrocarbon potential of the onshore Northern Perth basin, western Australia: Geological Survey of Western Australia Report 43, 67 p.</ref>
|-
| Carnarvon Basin, Australia || Low/Moderate || Permian || ? || Crostella<ref name=Crostella_1995b>Crostella, A., 1995, Structural evolution and hydrocarbon potential of the Merlinliegh and Byro sub-basins, Canarvon basin, western Australia: Geological Survey of Western Australia Report 45, 35 p.</ref>
|-
| Khorat Plateau basin, Thailand-Laos || Low || Triassic/Jurassic || ? || Smith and stokes<ref name=Smithandstokes_1997>Smith, P. F. L., and R. B. Stokes, 1997, Geology and petroleum potential of the Khorat Plateau Basin in the Vientiane area of Lao P.D.R.: Journal of Petroleum Geology, v. 20, p. 27-50.</ref>
|-
| colspan=5 | <div style="text-align: center;">'''SOUTH ASIA'''</div>
|-
| Vendian basin, India || Low/Moderate || Precambrian || ? ||
|-
| Suliaman range foreland, Pakistan || Low || Cretaceous || Direct ? ||
|-
| colspan=5 | <div style="text-align: center;">'''MIDDLE EAST'''</div>
|-
| Risha area, Jordan || High || Ordovician || Indirect || Ahlbrandt et al.<ref name=Ahlbrandtetal_1997>Ahlbrandt, T. S., O. A. Okasheh, and M. Lewan, 1997, A Middle East basin center hydrocarbon accumulation in Paleozoic rocks, eastern Jordan, western Iraq, and surrounding areas (abs.): AAPG International Conference and Exhibition, p. A1-A2.</ref>
|-
| colspan=5 | <div style="text-align: center;">'''AFRICA'''</div>
|-
| Ahnet basin, Algeria || High || Cambrian/Ordovician || Indirect ||
|-
| Benue trough, Nigeria || Moderate/High || Cretaceous || Direct || Obaje and Abaa<ref name=Obajeandabaa_1996>Obaje, N. G., and S. I. Abaa, 1996, Potential for col-derived gaseous hydrocarbons in the middle Benue Trough of Nigeria: Journal of Petroleum Geology, v. 19, p. 77-94.</ref>
|}
|}
===Indirect systems===
===Indirect systems===
In contrast to direct systems, indirect systems require a liquid-prone source rock ([[:file:BasinCenteredGasFig1.jpg|Figure 1]]). Reservoir quality in indirect systems is assumed to have been better than in direct systems. In this case, oil and gas are generated and expelled and migrate to reservoirs where they accumulate in structural and stratigraphic traps as discrete, buoyant accumulations with downdip water contacts. With subsequent burial and exposure to higher temperatures, the accumulated oil undergoes thermal cracking to gas, accompanied by a significant increase of fluid volume and pressures (Barker<ref name=Barker_1990>Barker, C., 1990, [http://archives.datapages.com/data/bulletns/1990-91/data/pg/0074/0008/0000/1254.htm Calculated volume and pressure change during the thermal cracking of oil to gas in reservoirs]: AAPG Bulletin, v. 74, p. 1254-1261.</ref>). The level of thermal maturity at which oil is transformed to gas is commonly thought to be about 1.35% vitrinite reflectance (Ro) (Tissot and Welte,<ref name=Tissotandwelte_1984>Tissot, B. P., and D. H. Welte, 1984, Petroleum formation and occurrence, 2d rev. ed.: Berlin, Springer-Verlag, 699 p.</ref> Hunt<ref name=Hunt_1996>Hunt, J. M., 1996, Petroleum geochemistry and geology, 2d ed.: New York, W. H. Freeman and co., 743 p.</ref>); however, some evidence, discussed in a following section, indicates that the transformation may occur at higher levels of thermal maturity. Alternatively, gas derived from thermally cracked oil within a source rock may subsequently be expelled and migrate to low-permeability reservoirs (Garcia-Gonzales et al.,<ref name=Garciagonzalesetal_1993a>Garcia-Gonzales, M., D. B. MacGowan, and R. C. Surdam, 1993, Coal as a source rock of petroleum and gas-a comparison between natural and artificial maturation of the Almond Formation coals, Greater Green River basin in Wyoming, ''in'' D. G. Howell, ed., [http://pubs.er.usgs.gov/publication/pp1570 The future of energy gases]: U.S. Geological Survey Professional Paper 1570, p. 405-437.</ref><ref name=Garciagonzalesetal_1993b>Garcia-Gonzales, M., D. B. MacGowan, and R. C. Surdam, 1993, Mechanisms of petroleum generation from coal, as evidenced from petrographic and geochemical studies: Examples from Almond Formation coals in the Greater Green River basin, ''in'' B. Strook and S. Andrew, eds., Wyoming Geological Association Jubilee Anniversary Field Conference Guidebook, p. 311-323.</ref> MacGowan et al.,<ref name=Macgowanetal_1993>MacGowan, D. B., M. Garcia-Gonzales, D. R. Britton, and R. C. Surdam, 1993, Timing of hydrocarbon generation, organic-inorganic diagenesis, and the formation of oabnormally pressured gas compartments in the Cretaceous of the Greater Green River basin: A geochemical model, ''in'' B. Strook and S. Andrew, eds., Wyoming Geological Association Jubilee Anniversary Field Conference Guidebook, p. 325-357.</ref> Hunt<ref name=Hunt_1996 />). Under these conditions of changing fluid volume and pressure, the capillary pressure of the water-wet pore system is exceeded, and, like pore pressures in direct systems, the high pressures forcibly expel mobile, free water from the pore system, replacing water with gas, and the development of an overpressured BCGA ensues. An additionally important aspect of this phase is the necessity for the presence of an effective lithologic top seal in reservoirs formerly occupied by discrete oil accumulations.
==Phase III==
==Phase III==
At the point where direct and indirect systems are in the overpressured phase (phase II), the processes involved in the transition to phase III are identical for both systems ([[:file:BasinCenteredGasFig1.jpg|Figure 1]]). Phase III occurs when the overpressured phase of direct and indirect systems evolves into underpressured conditions. Both systems, subsequent to the phase II history of overpressure, may experience a period of uplift and erosional unloading and/or heat flow perturbations. During, or subsequent to, these burial and thermal history disruptions, some gas is lost from the accumulation, and the overpressured gas reservoirs are subjected to reduced temperatures. The loss of gas, in conjunction with reduced temperatures, effectively results in the development of an underpressured BCGA (Meissner,<ref name=Meissner_1978 /> Law and Dickinson<ref name=Lawanddickinson_1985 />). During this pressure transition, Meissner<ref name=Meissner_2000>Meissner, F. F., 2000, Causes of anomalous deep basin fluid pressures in Rocky Mountain basins and their relation to regional gas accumulation, ''in'' 2000 basin-centered gas symposium: Rocky Mountain Association of Geologists, 11 p.</ref> emphasized the importance of gas loss over temperature reduction as the dominant process.
Conjectural evidence concerning the integrity of seals in direct vs. indirect systems implies that gas is lost more easily from direct BCGAs than from indirect BCGAs. Johnson et al.<ref name=Johnsonetal_1994>Johnson, R. C., D. D. Rice, and T. D. Fouch, 1994, Evidence for gas migration from Cretaceous basin-centered accumulations into lower Tertiary reservoirs in Rocky Mountain basins: Proceedings of the Rocky Mountain Association of Geologists and Colorado Association First Biennial Conference, Natural Gas in the Western United States, 8 p.</ref> have shown that gas in conventionally trapped accumulations in several Rocky Mountain basins originated from BCGAs, demonstrating that loss of gas through relative permeability, capillary pressure seals does occur. Examples of underpressured, phase III direct systems include Cretaceous rocks in the San Juan, Raton, and Denver basins, and examples of underpressured, phase III indirect systems include Lower Silurian reservoirs in the Appalachian basin, Ordovician reservoirs in the Risha area of eastern Jordan, and Cambrian and Ordovician reservoirs in the Ahnet basin of Algeria (Table 1).
==Phase IV==
==Phase IV==
Phase IV is theoretical and may be more applicable to direct systems because of the perceived, relatively better quality of seals in indirect systems than seals in direct systems. During phase IV, continued loss of gas from capillary pressure seals in BCGAs is accompanied by water slowly reentering underpressured, gas-bearing reservoirs. Under these conditions, Meissner<ref name=Meissner_1978 /> and Law and Dickinson<ref name=Lawanddickinson_1985 /> hypothesized that the underpressured, gas-bearing reservoirs would eventually evolve into normally pressured, water-bearing reservoirs, thus completing the pressure cycle.
==References==
==References==