The lack of production in the Marfa basin remains an enigma. Although covered with approximately 3,000 ft of thick volcanics, the basin has Paleozoic stratigraphy and lithologies similar to the prolific Delaware basin to the east. In a geologic and geophysical review, we analyzed the overall hydrocarbon potential for this basin.

The lower Paleozoic (Cambrian through Devonian) rocks, which are conducive to hydrocarbon generation in other Permian basins, have many undrilled structures, as revealed by seismic mapping, but have also pervasive fresh water and dead oil. Several fault systems are mapped on the surface. We believe that the rocks were uplifted in Late Mississippian and Pennsylvanian time and in certain areas were exposed to meteoric water. Hydrocarbons leaked out along with induction of fresh water into the formations. Recharge areas have been identified from isopach maps. In certain parts, the lower Paleozoic rocks are overmature and offer further obstacles to exploration.

During the Early Permian, arkosic sediments were deposited in a rapidly subsiding east-west graben. Tilted to the south, the graben accumulated as much as approximately 9,000 ft of Lower Permian sediments that have occasional hydrocarbon shows. Small stratigraphic traps due to pinchouts, truncations, and facies changes are to be expected in these rocks. Possible reef growths in the Late Permian offer further opportunities for trap development.

The rocks were also exposed to meteoric water during nondeposition in the Triassic, Jurassic, and post-Cretaceous periods. However, the subtle Permian traps, being small, could have escaped destruction and freshwater flushing and thus might offer some potential for future exploration.

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