The Delaware-Val Verde basins lie as a continuous elongate northwest-southeast-trending downwarp extending from Eddy County in southeast New Mexico to Edwards and Kinney Counties, Texas. Deep production is confined primarily to gas-condensate reservoirs in the Ellenburger Group of the Ordovician; the Devonian; the Morrowan, Atokan, and Strawn Series of the Pennsylvanian; and the Wolfcampian Series of the Permian. Significant structures include the Brown-Bassett, Bell Lake, Coyanosa, Hershey, Puckett, Rojo Caballos, Toyah, and Worsham-Bayer Fields.

Post-Precambrian geologic history began with a shallow embayment in Cambro-Ordovician time which was followed by the development of the Tobosa basin in the Middle and Upper Ordovician epochs and Siluro-Devonian periods. Epeirogenic uplift in the middle to late Devonian gave rise to a widespread erosional unconformity. Subsequent deposition of Mississippian and early Pennsylvanian sediments was without tectonic incident. In middle to late Atokan time (early Pennsylvanian), severe folding and thrusting occurred in the Ouachita geosyncline and Marathon region, to the south. This rising mountainous area resulted in a flood of Permo-Pennsylvanian clastic sediments which filled the Delaware-Val Verde trough. Renewed uplift of the Diablo and Central Basin platforms and thrusting in the Ouach ta-Marathon region in mid-Wolfcampian time culminated the early history of the Delaware-Val Verde basins. Later tectonic influences--which help account for fluid distribution--include the regional upwarp of the Diablo platform, Marathon uplift, and Ouachita folded belt in the Triassic-Jurassic periods, along with late Cretaceous faulting and Tertiary igneous activity.

Original distribution of the water salinity in the Ellenburger and Devonian zones appears to have been highly modified by subsequent hydrodynamic movement of meteoric waters in the west, southwest, and south portions of the trough. This flushing, extremely active in early Pennsylvanian, late Permo-Pennsylvanian, and Triassic-Jurassic periods, continued to a lesser degree to the present time. Charged meteoric waters introduced carbon dioxide which had as its major origin the solution of carbonate and bicarbonate components in the exposed rocks of the Ouachita, Marathon, and Diablo platform areas. The most likely periods of generation were early Pennsylvanian, late Permo-Pennsylvanian, and during the Tertiary igneous disturbance. Forceful emplacement of carbon dioxide and methane may ha e occurred in the Val Verde basin throughout the time of early Pennsylvanian and mid-Wolfcampian folding and thrusting in the Ouachita-Marathon region.

Absence of oil production from the deep zones in the Delaware and Val Verde basins appears to be the result of two major factors. The first is the hydrodynamic flushing of crude-oil accumulations from all but the deeper and large closures. This scattering of oil occurred coincident with the major periods of hydrodynamic activity. The second factor is that restored maximum overburden, as well as present overburden in many cases, exceeds the gas-condensate conversion point for Delaware-Val Verde basin oils. These oils, derived from the Simpson, Woodford, and Permo-Pennsylvanian shales, disassociate into gas-condensate and gas below depths of 14,000, 13,000 and 8,000 to 9,000 ft, respectively.