Possible Future Petroleum Potential of Pre-Jurassic, Western Gulf Basin: Region 6

In the western Gulf basin, the pre-Jurassic section can be subdivided as follows: (1) Paleozoic foreland sedimentary rocks (Black Warrior basin); (2) orogenic geosynclinal facies (Ouachita tectonic belt); (3) late orogenic strata, late Paleozoic; and (4) postorogenic strata, Late Triassic. A good potential for discovery of future petroleum provinces of economic interest can be recognized in the Black Warrior basin and in late orogenic, late Paleozoic sedimentary strata on the Gulf of Mexico side of the Ouachita tectonic belt. A remote possibility is recognized for the presence of commercial accumulations of hydrocarbon in subthrust lower Paleozoic foreland carbonate rocks beneath the interior part of the Ouachita fold belt. The hydrocarbon potential of geosynclinal sedimentary rocks of the Ouachita tectonic belt and of the postorogenic Triassic section is considered to be negligible. The Black Warrior basin of Mississippi and Alabama contains a thick section of Paleozoic foreland sedimentary beds. Although production dates back to 1909, and hydrocarbon shows have been numerous, the proved reserves of the basin are insignificant. The deep structural configuration has been difficult to map, and this has deterred deep drilling. The basin tectonics should be comparable to those of the other foreland basins, in which large, buried normal faults are characteristic. Improved seismic techniques should reveal similar anomalies in the Black Warrior basin. Large hydrocarbon accumulations ultimately may be found in deep fault traps in lower Paleozoic carbonate rocks; such prospects are sparsely tested. There is no production from pre-Jurassic rocks gulfward from the Ouachita front. However, exploration of this section has been limited, mainly because of the absence of attractive objectives. Most wells drilled below the Jurassic have encountered either tight, highly deformed, geosynclinal-facies rocks of the Paleozoic Ouachita system or redbeds and igneous rocks of the Late Triassic Eagle Mills Formation. Since 1960 a few highly significant, but unpublicized, wildcats have penetrated relatively undeformed, very fossiliferous, shallow-water shelf carbonate and clastic beds of Pennsylvanian age beneath the coastal plain. These strata, identified as Desmoinesian from fusulinids, are present on the Gulf of Mexico side of the Ouachita fold belt in wells drilled in northeast Texas and southwest Arkansas. Commercial porosities have been encountered in both sandstone and carbonate rock. Only fragmentary data are available, but the presence of these sedimentary rocks suggests the possibility of a potentially large, virtually unexplored, petroleum province in late Paleozoic rocks of the Gulf coastal plain. A recent 20,000-ft (6,096 m) test in Texas penetrated thick lower Paleozoic shelf carbonate rocks on a large seismic anomaly beneath the interior zone of the Ouachita system. Although the objective carbonate rocks were metamorphosed there, the possibility of encountering favorable reservoir rock elsewhere in this trend was not necessarily eliminated.