Basin-centered gas systems: historical development and classification

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Basin-centered gas systems
Series AAPG Bulletin, November 2002
Author Ben E. Law
Link Web page

Of all the different types of unconventional gas systems, none have been more poorly defined than BCGSs. The problem of definition has led to misconceptions that have, in some cases, impeded exploration efforts. When regionally pervasive gas accumulations, like BCGAs, became known is uncertain; however, Silver[1] alluded to pervasive gas accumulations in Cretaceous rocks in the San Juan basin of New Mexico and Colorado and recognized the gas-saturated nature of the reservoirs and the downdip absence of water. Later, the nuclear stimulation experiments conducted in the United States from 1967 to 1973 seem to have implied knowledge of the presence of regionally pervasive gas-charged reservoirs, although there are no geologic reports confirming this assumption. Nuclear detonations conducted in Cretaceous rocks in the San Juan and Piceance basins of New Mexico and Colorado were unsuccessful, and eventually, because of concerns about environmental and radioactive contamination issues, the tests were abandoned.[2][3][4][5]

The first published, unmistakable reference to this type of gas accumulation was by Masters.[6] In his article, Masters identified the basic concepts of basin-centered gas accumulations, referring to them as deep basin gas, and provided several defining characteristics of gas-saturated reservoirs in the deep basin of Alberta, Canada, and in the San Juan basin of New Mexico and Colorado as examples of such accumulations. Later, in a publication edited by Masters,[7] the various geologic aspects of the so-called deep basin gas accumulation in the Elmworth field of Alberta, Canada, were provided. Other significant early articles concerning BCGAs include those by Law et al.[8][9] and Law[10] in the Greater Green River basin of Wyoming, Colorado, and Utah, and McPeek[11] in the Great Divide basin of Wyoming. Spencer[12][13] and Law and Spencer[14] described many of the attributes common to BCGAs. Several examples of so-called tight gas reservoirs (in most cases equivalent to BCGAs) in the United States are provided in a volume edited by Spencer and Mast.[15] Finley[16] and Dutton et al.[17] also described many additional low-permeability reservoirs.

When the term basin-centered gas accumulations came into use is uncertain; however, the first published reference to the term was by Rose et al.[18] in a study of gas accumulations in the Upper Cretaceous Trinidad Sandstone of the Raton basin. It is likely, however, that the term basin-centered gas accumulations had been informally used by industry people prior to the first published reference of the name.

The term tight gas sands has been widely used to describe BCGAs for many years, and many exploration geologists still use that term. In many cases tight gas sands is an appropriate term; however, it is somewhat ambiguous and may include gas accumulations that are trapped as conventional, buoyant accumulations. The use of the term deep basin gas[6] has some problems also because all BCGAs do not occur at great depths. For example, much of the gas production in the San Juan basin is from BCGAs at depths as shallow as 3000 ft (914 m). More recently, the term deep basin gas has been defined as those gas accumulations deeper than 15,000 ft (4572 m);[19] it is an economic definition and is not based on geologic processes. Finally, the term continuous gas accumulation,[20] although accurately portraying the pervasive nature of BCGAs, is too broad and includes such gas systems as coalbed methane and shale gas.

References

  1. ↑ 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.
  2. ↑ Randolph, P. L., 1973, Nuclear stimulation of gas fields: Canadian Gas Association, National Technical Conference, 21 p.
  3. ↑ Randolph, P. L., 1974, Massive stimulation effort may double U.S. gas supply, part 1: World Oil, v. 179, no. 4, p. 65-71.
  4. ↑ Randolph, P. L., 1974, Massive stimulation effort may double U.S. gas supply, part 2: World Oil, v. 179, no. 5, p. 131-134.
  5. ↑ Randolph, P. L., 1974, Massive stimulation effort may double U.S. gas supply, part 3: World Oil, v. 179, no. 6, p. 81-84.
  6. ↑ 6.0 6.1 Masters, J. A., 1979, Deep basin gas trap, western Canada: AAPG Bulletin, v. 63, p. 152-181. Cite error: Invalid <ref> tag; name "Masters_1979" defined multiple times with different content
  7. ↑ Masters, J. A., ed., 1984, Elmworth: case study of a deep basin gas field: AAPG Memoir 38, 316 p.
  8. ↑ Law, B. E., C. W. Spencer, and N. H. Bostick, 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.
  9. ↑ 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.
  10. ↑ 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.
  11. ↑ McPeek, L. A., 1981, Eastern Green River basin-a developing giant gas supply from deep, overpressured Upper Cretaceous sandstones: AAPG Bulletin, v. 65, p. 1078-1098.
  12. ↑ Spencer, C. W., 1985, Geologic aspects of tight gas reservoirs in the Rocky Mountain region: Journal of Petroleum Geology, p. 1308-1314.
  13. ↑ Spencer, C. W., 1989, Review of characteristics of low-permeability gas reservoirs in western United States: AAPG Bulletin, v. 73, p. 613-629.
  14. ↑ 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: U.S. Geological Survey Professional Paper 1570, p. 233-252.
  15. ↑ Spencer, C. W., and R. F. Mast, eds., 1986, Geology of tight gas reservoirs: AAPG Studies in Geology 24, 299 p.
  16. ↑ Finley, R. J., 1984, Geology and engineering characteristics of selected low-permeability gas sandstones: a national survey: Texas Bureau of Economic Geology Report of Investigations 138, 220 p.
  17. ↑ Dutton, S. P., S. J. Clift, D. S. Hamilton, H. S. Hamlin, T. F. Hentz, W. E. Howard, M. S. Akhter, and S. E. Laubach, 1993, Major low-permeability sandstone reservoirs in the continental United States: Texas Bureau of Economic Geology Report of Investigations 211, 221 p.
  18. ↑ Rose, P. R., J. R. Everett, and I. S. Merin, 1986, Potential basin-centered gas accumulation in Cretaceous Trinidad Sandstone, Raton basin, Colorado, in C. W. Spencer and R. F. Mast, eds., Geology of tight gas reservoirs: AAPG Studies in Geology 24, p. 111-128.
  19. ↑ Dyman, T. S., D. D. Rice, and P. A. Westcott, eds., 1997, Geologic controls of deep natural gas resources in the United States: U.S. Geological Survey Bulletin 2146, 239 p.
  20. ↑ Schmoker, J. W., 1996, Method for assessing continuous-type (unconventional) hydrocarbon accumulations, in D. L. Gautier, G. L. Dolton, K. I Takahashi, and K. L. Varnes, eds., 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.

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