17-8 Geological advances driven by resource development of subsurface Leonardian (lower Permian) deep-marine sandstones, siltstones and organic-rich mudrocks, Midland Basin, west Texas

Session: One Century of Oil and Gas in the Permian Basin

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Geological research on the Midland Basin, the eastern subbasin of the greater Permian Basin, west Texas, has been ongoing for over 100 years. Early outcrop work identified Leonardian (Lower Permian) sedimentary rocks, and in 1923, the dramatic, widely promoted Santa Rita #1 “blew in”, and the Permian Basin became one of the world’s best-studied subsurface sedimentary basins.

Little production was derived from Leonardian deep-water basinal rocks until the 1949 discovery of oil on the Sprayberry lease in Dawson County. This ‘Spraberry’ oil was produced from produced from naturally fractured, low porosity-low-permeability siltstone and very fine-grained sandstone reservoirs over a vast area, such that it was hard to drill a dry hole. However, the Spraberry was underpressured had low porosity and permeability and unimpressive per-well flow rates: an average of 7 barrels (bbl) of oil per day was produced from approximately 8,900 vertical wells. Nonetheless, the 1950’s Spraberry drilling boom provided fundamental knowledge of lithofacies, natural fractures, and initial basinwide isopach maps. Little was known about the deep-marine origin of Midland Basin Leonardian strata. However, the inference that glacio-eustatic sea-level changes resulted in alternating lowstand (sandy-silty siliciclastic deposition) and highstand systems tracts was proposed.

By 1960, conventional Sprayberry drilling and production had plateaued from its early ‘50’s peak and waterflooding operations were underway. Leonardian geologic research waned, although notable papers on deep-water sedimentary processes and mass transport processes and deposits in deep marine basins moved research ahead in the 1970’s and 1980’s. The 1990’s Leonardian focus remained on enhanced oil recovery from the Spraberry siltstones and sandstones.

In the early 2000’s, the ability to comingle Spraberry and underlying Wolfcampian zones and higher oil prices fueled the emergence of the “Wolfberry” vertical-well play. About 90% of Wolfberry production was derived from Spraberry siltstones and sandstones. Vertical drilling gave way to horizontal drilling and hydraulic fracturing circa 2014-2015, and Leonardian oil production has more than quadrupled since then, from under 100,000 bbl/day to over 400,000 bbl/day. Most of the oil produced ‘unconventionally’ in this manner now comes from the highstand shaly zones (Lower and Middle Leonard units). This recent activity has sparked the modern era of renewed interest in Leonardian research, including focus on integration of core sedimentology and geochemistry, petrophysics, and seismic attributes.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-11260

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