ABSTRACT

The Midland Basin of west Texas contains numerous large conventional oil and gas fields, including the giant Kelly -Snyder field (Penn. reef, Horseshoe Atoll) and Spraberry Trend (early Permian deep-water clastics). Recently, the Wolfcamp shale and Spraberry Formation have emerged as two of the nation’s leading unconventional plays. Bounded by the Lower Strawn Limestone below and by middle Permian units above, this thick (~4,000 ft.) package of strata record the history of basin-fill during Late Pennsylvanian - early Permian time. To facilitate the development of these massive unconventional resources, the Wolfcamp – Spraberry interval is now informally subdivided into a number of lithostratigraphic-based operational units and sub-units. Major units include, from oldest to youngest, the Wolfcamp D, Wolfcamp C, Wolfcamp B, Wolfcamp A, Dean, Lower Leonard Shale, Jo Mill, and the Lower, Middle, and Upper Spraberry.

The Wolfcamp D consists of a series of semi-starved, basinal cyclothems deposited during the Late Pennsylvanian icehouse. The Wolfcamp C is a predominantly clay-rich shale representing the distal portions of large delta systems that rapid prograded across the Eastern Shelf. During the upper portion of Wolfcamp C time, the Glasscock Nose was constructed by a series of mounded/progradational deep water carbonate flows (carbonate drift deltas?).  Concurrently, regional structural movements within the Central Basin Uplift resulted in formation of the mid-Wolfcamp unconformity along the western flank of the Midland Basin.  The Wolfcamp B and Wolfcamp A constitute a thick series of organic-rich, silt- and calcareous-rich mud rocks currently residing in the peak oil generative window. Deposition of the Wolfcamp shale was terminated by the first major incursion of deep-water clastics, represented by the Dean sandstone. This was followed by deposition of the Lower Leonard shale, Jo Mill, Lower Spraberry, Middle Spraberry, and Upper Spraberry, a series of silty mudstones and clay-rich siltstones punctuated by numerous deep-water submarine fan complexes containing massive to laminated, fine-grained sandstones. The Dean through Upper Spraberry units are stratigraphically-equivalent to the Bone Spring of the Delaware Basin.

Each Wolfcamp – Spraberry operational unit is geologically unique, the product of a dynamic set of tectonic, climatic, sedimentologic, oceanographic, and biological factors that characterize the Late Pennsylvanian – early Permian setting of western Pangea.  Analysis of regional sea-level curves tie specific operational units to particular periods of long-term lowstands and highstands encapsulating the Late Pennsylvanian icehouse and transition to an early Permian greenhouse. Understanding of the regional geologic setting and sea-level history of these rocks helps unravel the complex lithologies and stratigraphy observed on seismic, logs, and in cores. Recognition of the geologic uniqueness of each operational unit also assists geologists and engineers during the drilling, targeting, completion, and development phases of these important unconventional resources.

BIOGRAPHY

Lowell Waite is currently a Lecturer in the Department of Geosciences and Co-Director of the Permian Basin Research Lab at the University of Texas at Dallas. He received his B.S. degree (Geology major) from the University of Michigan and an M.S. in Geology from the University of Texas at Arlington. From 1981 to 1998 he was employed by Mobil Oil Corp., and by Pioneer Natural Resources from 1998 to 2019. Lowell has held several positions in carbonate research and domestic and international E & P, studying a number of classic petroleum regions including North Africa, Saudi Arabia, Kazakhstan, Venezuela, Mexico, U.S. Gulf of Mexico, and the Permian Basin. His focus at UT Dallas is to provide education on petroleum systems and basins to better prepare students for employment in the oil and gas industry.

Lowell served in the United States Navy Reserve from 1992 – 2000. He is a member of the AAPG, SEPM, GSA, SIPES, and the Dallas Geologic Society.