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The Val Verde basin is a northwest-southeast trending foreland basin contained within the southern portion of the Permian basin. The Val Verde basin has several large fields, e.g., Brown Bassett and JM, which have a combined ultimate recovery of over 1 tcf of gas. Structurally, the major fields are complexly faulted features related to differential uplift of basement blocks. Vertical and horizontal displacement resulted from a wrench system dominated by northwest and northerly trending faults. Reverse faults associated with the wrench system appear to exhibit characteristics of both high-angle and low-angle faults, as is typical of foreland structures. Tectonism was initiated during the late Mississippian, consequent to Ouachita plate convergence, and continued into the P rmian.
Middle and Upper Permian strata are not present in the central and southern Val Verde basin. Appreciable amounts of Permian sediment were eroded prior to deposition of Cretaceous strata, thus, Cretaceous rocks unconformably overlie Wolfcamp sediments. Restored estimates for vitrinite reflectance data indicate a minimum of 8,000-10,000 ft (2,400-3,000 m) of Permian rocks have been eroded. Therefore, in the central and southern portions of the basin, Paleozoic rocks are inferred to have occupied depths several miles deeper than present. Vitrinite reflectance values for Ellenburger (Ordovician) rocks at Brown Bassett are approximately 1.8 to 2.0% Ro. Ellenburger reflectance values increase to the south and southeast to values greater than 4.5% Ro. The most southerly wells also have reflectance depth trends which show a break in gradient within Wolfcamp sediments (9,000-10,000 ft, 2,700-3,000 m). The change in gradient suggests a thermal event contemporaneous with the basin's rapid downwarping and Wolfcamp deposition.
Any exploration in the basin, therefore, must recognize the unique relationships between structural timing, structural position, depth of burial, thermal pulses, and hydrocarbon mobility for a large portion of the Val Verde basin.
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