Petroleum reservoirs typically yield only a fraction of the oil initially in place because geologic heterogeneity causes incomplete drainage of oil. Accurately predicting oil recovery requires realistic estimates of interwell porosity and permeability patterns that are discontinuous in both the horizontal and the vertical direction. Results of this study, which show the effects of heterogeneity on fluid flow and oil recovery efficiency through several simulation experiments, are applicable to many other carbonate and noncarbonate fields worldwide.

The Hueco Basin of Trans-Pecos Texas and Chihuahua, Mexico, formed in response to Basin and Range extensional tectonism that began about 24 Ma ago and continues to the present. The basin is curvilinear, with the northwestern part of the basin trending north to south and the southeastern part trending northwest to southeast. The Campo Grande fault is located in the southeastern part of the basin. Here the basin is asymmetrical, the thickest sediments having been deposited along the fault-bounded basin axis near the southwestern flank.

The Ellenburger Group (Lower Ordovician) of Texas is a laterally extensive peritidal carbonate shelf sequence. It forms a major deep oil reservoir, having estimated reserves of 1.15 billion barrels of oil, and it also contains an estimated 2.2 billion barrels of oil equivalent.

To recover gas remaining in solution, large volumes of brine must be produced from watered-out gas reservoirs in the Gulf Coast. Secondary gas recovery in a geopressured upper Frio (Oligocene) reservoir in Northeast Hitchcock and Alta Loma fields in Galveston County, Texas, requires the disposal of approximately 20,000 barrels of brine per day (bblld) into several disposal wells.