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Line 179: − − Worldwide, there are only a few references available alluding to the presence of BCGAs (Table 1). Many more areas undoubtedly contain BCGAs, but because of the poor understanding of the concepts of BCGSs in countries outside North America, the global distribution of BCGAs is poorly known. For example, in North America, many Rocky Mountain basins contain direct BCGAs. By analogy with Rocky Mountain basins, it is likely that many of the Andean foreland basins of South America also contain BCGAs. Several of the basins in the Middle East and North Africa probably contain indirect BCGAs similar to those in Jordan and Algeria.
Basin-centered gas systems: global distribution (view source)
Revision as of 00:09, 30 January 2015
, 00:09, 30 January 2015no edit summary
[[file:BasinCenteredGasFig13.jpg|thumb|400px|{{figure number|1}}Map of the United States showing the geographic distribution of known and potential BCGAs.]]
[[file:BasinCenteredGasFig13.jpg|thumb|400px|{{figure number|1}}Map of the United States showing the geographic distribution of known and potential BCGAs.]]
The global distribution of basin-centered gas accumulations (BCGAs) is poorly known, and knowledge of the stratigraphic distribution of BCGAs is incomplete. Even in North America, where most of the exploration activity for BCGAs has occurred, the geographic distribution is not well known. [[:file:BasinCenteredGasFig13.jpg|Figure 1]] shows the locations of known and suspected BCGAs in the United States. A tabulation of these areas, as well as areas outside North America, is shown in Table 1. The geographic distribution of BCGAs is probably best known in the Rocky Mountain region, where a considerable amount of research has occurred.
The global distribution of basin-centered gas accumulations (BCGAs) is poorly known, and knowledge of the stratigraphic distribution of BCGAs is incomplete. Even in North America, where most of the exploration activity for BCGAs has occurred, the geographic distribution is not well known. [[:file:BasinCenteredGasFig13.jpg|Figure 1]] shows the locations of known and suspected BCGAs in the United States. A tabulation of these areas, as well as areas outside North America, is shown in Table 1. The geographic distribution of BCGAs is probably best known in the Rocky Mountain region, where a considerable amount of research has occurred.
Worldwide, there are only a few references available alluding to the presence of BCGAs (Table 1). Many more areas undoubtedly contain BCGAs, but because of the poor understanding of the concepts of BCGSs in countries outside North America, the global distribution of BCGAs is poorly known. For example, in North America, many Rocky Mountain basins contain direct BCGAs. By analogy with Rocky Mountain basins, it is likely that many of the Andean foreland basins of South America also contain BCGAs. Several of the basins in the Middle East and North Africa probably contain indirect BCGAs similar to those in Jordan and Algeria.
{| class = "wikitable"
{| class = "wikitable"
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| 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>
| 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>
|}
|}
The stratigraphic distribution of BCGAs extends from the Cambrian through the Eocene (Table 1). However, there appear to be some differences in the stratigraphic distribution of direct and indirect BCGAs. For example, the preponderance of direct BCGAs occur in Cretaceous through Eocene rocks (Table 1), whereas indirect BCGAs more commonly occur in pre-Cretaceous rocks. Although some of the apparent difference in stratigraphic distribution may be attributable to the disproportionate number of studies in Cretaceous and younger rocks compared to numbers of studies in pre-Cretaceous rocks, the question of seal integrity in direct systems arises. As previously discussed, the effective life of capillary pressure seals in direct systems is not known; therefore, because of the perceptions of a leaky seal in direct systems, the occurrence of direct systems in pre-Cretaceous rocks may be less common than in Cretaceous and younger rocks. Some examples, however, of pre-Cretaceous direct BCGAs include Permian rocks in the Timan-Pechora basin, Russia (Law et al., 1996), and the Sichuan basin, China (Da-jun and Yun-ho, 1994); Pennsylvanian rocks in the Arkoma basin (Meckel et al., 1992); and Carboniferous rocks in the Dnieper-Donets basin, Ukraine (Law et al., 1998b) (Table 1).
The stratigraphic distribution of BCGAs extends from the Cambrian through the Eocene (Table 1). However, there appear to be some differences in the stratigraphic distribution of direct and indirect BCGAs. For example, the preponderance of direct BCGAs occur in Cretaceous through Eocene rocks (Table 1), whereas indirect BCGAs more commonly occur in pre-Cretaceous rocks. Although some of the apparent difference in stratigraphic distribution may be attributable to the disproportionate number of studies in Cretaceous and younger rocks compared to numbers of studies in pre-Cretaceous rocks, the question of seal integrity in direct systems arises. As previously discussed, the effective life of capillary pressure seals in direct systems is not known; therefore, because of the perceptions of a leaky seal in direct systems, the occurrence of direct systems in pre-Cretaceous rocks may be less common than in Cretaceous and younger rocks. Some examples, however, of pre-Cretaceous direct BCGAs include Permian rocks in the Timan-Pechora basin, Russia (Law et al., 1996), and the Sichuan basin, China (Da-jun and Yun-ho, 1994); Pennsylvanian rocks in the Arkoma basin (Meckel et al., 1992); and Carboniferous rocks in the Dnieper-Donets basin, Ukraine (Law et al., 1998b) (Table 1).