Dean Formation, Permian Basin

General Setting

The Leonardian Dean Formation in the Permian Basin is a major oil producer. Together with the overlying Spraberry Formation in what is known as the Spraberry Trend, the two contain more than 10 Bbbl of oil as of 2010 (Bureau of Economic Geology, n.d.). The name “Dean Sandstone” was first applied to a sandstone found in the Gulf Oil Corporation’s Dean No. 1 samples from 7,990 to 8,190 feet (McLennan and Bradley, 1951). The Dean Formation has a similar depositional history to the overlying Spraberry Formation, both co-located in a submarine fan system (Tyler et al., 1997), resulting from channelized flow and suspension settling (Handford 1981). Both formations can be divided into three genetic sequences, each with several hundred feet of interbedded shale and carbonate overlain by sandstone and silts of roughly equal thickness (Handford, 1981). The terrigenous clastics that compromise the formations can be divided into four lithofacies of which descriptions can be found in Handford (1981). The various characteristics of these rocks suggest deposition from turbidity currents, and saline density under-and inter-flow currents. Though the Dean Formation has thick sand units, the formation is generally heterogeneous with low permeabilities, both of which will have to be taken into account when considering the formation for carbon storage.

References

Bureau of Economic Geology. n.d. Wolfberry and Spraberry Play Of The Midland Basin, /research/programs/starr/unconventional-resources/wolfberry-spraberry

Handford, C. 1981. Sedimentology and Genetic Stratigraphy of Dean and Spraberry Formations (Permian), Midland Basin, Texas. AAPG Bulletin. doi: 65. 10.1306/03B5962A-16D1-11D7-8645000102C1865D.

McLennan, L., Jr. ; Bradley, H.W. 1951. Spraberry and Dean Sandstones of West Texas 1: Geological Notes. AAPG Bulletin (1951) 35 (4): 899–908. doi: 10.1306/3D9341FF-16B1-11D7-8645000102C1865D.

Tyler,  N., Gholston, J. C., and Guevara, E. H. 1997. Basin Morphological Controls on Submarine-Fan Depositional Trends: Spraberry Sandstone, Permian Basin, Texas: The University of Texas at Austin, Bureau of Economic Geology, Geological Circular 97-6, 43 p. doi: 10.23867/gc9706D.

Prepared by Emily Moskal, 2020.