Cores and supporting petrophysical data from 20 wells in McAllen Ranch field were analyzed. This Vicksburg field lies in northern Hidalgo County near the south end of the Texas Gulf Coastal Plain on the downthrown block of a major growth fault that merges with a glide plane dipping 5 degrees to the east beneath the field. The analyses provided a base for interpreting depositional environments.We grouped cored strata into four facies: (1) prodelta shales, (2) distal delta-front sandstones and shales, (3) proximal delta-front sandstones, and (4) distributary-channel sandstones.

Extensively cored cyclic evaporites of the San Andres Formation (Guadalupian) of the Palo Duro Basin, Texas Panhandle, provided fundamental information for interpreting evaporite depositional processes. These evaporites preserve exceptionally sensitive indicators of water-level fluctuation in their depositional environment: (1) sedimentary fabrics that formed during evaporite deposition; (2) sedimentary features, surfaces, and insoluble residues that formed during evaporite dissolution; and (3) diagenetic overprints that formed during evaporite brine evolution.

Lake Meredith, which supplies water for domestic use to all major Texas cities on the Southern High Plains, exceeds State of Texas limits for chloride and sulfate content.

Low recovery efficiencies of sandstone reservoirs in the Jackson-Yegua Barrier/ Strandplain Sandstone play mark it as a large hydrocarbon resource target for advanced recovery techniques. Prado field, Jim Hogg County, South Texas, has produced more than 23 million barrels of oil and more than 32 billion cubic feet of gas from structural-stratigraphic traps in barrier/strandplain sandstones of the Eocene lower Jackson Group. Recovery efficiency is 34 percent from the primary oil reservoir and 72 percent from the primary gas reservoir.