ABSTRACT: Formation of Clastic Reservoirs in the Queen Formation of the West Midland Basin of Texas

J. Harper, D. Newsom, A. Malicse, J. Mazzullo

The Queen Formation (Permian/Guadalupian) of the Midland basin is a sequence of interbedded back-reef shelf evaporites and clastics. Cores and logs of the upper Queen from Concho Bluff and Concho Bluff North fields in the western Midland basin were examined to determine the depositional history of its clastic members and the origins of its clastic hydrocarbon reservoirs.

The upper Queen contains 11.3 m of sheet clastics. The clastics are bounded by thick beds of laminated and chaotic anhydrite which were deposited in the subtidal areas of an extensive back-reef playa. The clastics consist of planar and wavy laminated fine sandstones and haloturbated and ripple-laminated siltstones and mudstones which are arranged into four stacked symmetrical cycles.

Each cycle grades from a basal silty mudstone to sandstone and then back to silty mudstone, and each records the progradation and retreat of a lobe of fluvial-deltaic sand flats and saline mud flats in and out of the playa.

The two Queen fields were formed by structural closures on a broad regional homocline. Within these closures, fluvial sand-flat deposits form reservoirs with average porosities and permeabilities of 16% and 45 md, whereas the mudstones, siltstones, and anhydrite form the seal of these reservoirs.

AAPG Search and Discovery Article #91003©1990 AAPG Annual Convention, San Francisco, California, June 3-6, 1990