Abstract The Spraberry Formation forms the heart of a multibillion-barrel oil field in the Midland Basin, west Texas. Production is from very fine sandstones and siltstones that form low-permeability and low-pressure reservoirs across eight counties in west Texas. The Sun Oil Co., Lottie Jalonick #1 core is continuous through the upper 222 feet (68 m) of the Spraberry Formation and is ideal for facies analysis. Four lithofacies comprise the terrigenous clastics of the Spraberry and Dean Formations: (1) cross-laminated, massive, and parallel-laminated sandstone, (2) laminated siltstone, (3) bioturbated siltstone, and (4) black, organic-rich shale. Silty dolomite mudstone is a very minor carbonate component. Though not common in other cores, numerous fining-upward sequences of sandstone overlain by shale and laminated siltstone are common in the Jalonick core. These are interpreted to be deposits from saline density currents, generated in shelf lagoons and salt pans, as they were dispersed beyond channel mouths in the distal fringe of an upper Spraberry submarine fan. Laminated siltstones were deposited out of suspension from saline density interflows.

Abstract The Permian (Leonardian) Upper Spraberry Formation in the Happy Field of Garza County, Texas, contains an excellent example of a reservoir composed of resedimented carbonates in a deep-water slope-basin setting. The field has one of the most complete data sets of any producing deep-water carbonate reservoir known, including 15 whole cores with matching full suites of electric logs, and high-resolution three-dimensional (3D) seismic data. Sequence stratigraphic analysis combined with detailed characterization of analogous outcrops, detailed core-based sedimentology, and well-log analysis indicate that the Happy Field ooid fans are positioned within the transgressive systems tract of the fifth composite sequence in the Leonardian. The main reservoir facies are resedimented ooid and skeletal grainstone hyperconcentrated density flows that were focused downslope through a probable reentrant in the shelf margin and deposited in a long-lived topographic depression at the toe-of-slope. Vertical heterogeneity is set up by laterally extensive shale and silt beds that punctuate the oolitic density flows. Lateral heterogeneity and compartmentalization within the reservoir are created by younger mixed carbonate-siliciclastic debris flows that are highly erosive and are characterized by relatively low permeability.