Abstract

Hydrocarbon production from reservoirs on University Lands in West Texas has been prolific, having a cumulative production of more than 1.5 billion stock tank barrels (BSTB). These reservoirs are located in the maturely explored Permian Basin, where reserve additions from existing fields greatly exceed reserves added from new discoveries. An integrated geologic and engineering assessment of the oil and gas resources in producing University Lands reservoirs was undertaken to ascertain the volumes of remaining oil and gas. Oil and gas reserves, remaining mobile oil, residual oil, and oil and gas-reserve growth potential were calculated within a geologic play framework.

Play analysis and resource assessment were performed on 101 oil reservoirs, each of which has produced more than 1 million stock tank barrels (MMSTB) of oil. Ninety-five percent of all oil production from University Lands has come from these 101 reservoirs, which are grouped into 17 geologic plays. They contained 7.25 BSTB of original oil-in-place, have produced 1.5 BSTB, and contain 0.2 BSTB of proved producible reserves. The remaining oil resource within these reservoirs, in excess of proved reserves, is 5.5 BSTB, of which 2.2 BSTB is mobile to waterflood and 3.3 BSTB is residual. Mobile oil reserve growth potential through the application of advanced recovery strategies is conservatively estimated to be 475 MMSTB. Miscible C02 enhanced oil recovery has the potential to add 436 MMSTB of reserves.

Gas resource assessment was applied to 85 associated and nonassociated University Lands reservoirs. These 85 reservoirs were classified within oil plays or, where applicable, in new gas plays. Total gas production from University Lands has exceeded 1 trillion cubic feet (Tcf), 953 billion cubic feet (Bcf) of which was produced from nonassociated reservoirs. The resource base includes 519 Bcf of reserves. Nonassociated reserves are 308 Bcf, the largest portion occurring in the Siluro/Devonian Carbonate and Ellenburger Tectonically Fractured Dolostone Gas plays. The associated gas-well-gas resource base contains 30 Bcf of reserves, the largest portion occurring in the Delaware Submarine Fan Sandstone play. Reserve growth potential is 213 Bcf for both associated and nonassociated gas reservoirs.