Petrography, Stratigraphic Framework and Depositional Environment of the Wolfcampian Carbonate Deposits on the Northwest Shelf and Midland Basin

Toyly Abdullyev¹, Merlynd Nestell¹, and Robert Trentham²

¹University of Texas at Arlington, Arlington, Texas

Abstract

The Wolfcampian name was first proposed for lowermost Permian strata by Cheney et al. (1945) and strata of this age has been an important target for oil exploration in West Texas. Exploration cores have been taken in a number of wells in the northern part of Northwest Shelf and northwestern margin of the Midland Basin in the 1960's and 1970's that have not been studied until recently. They have been stored at the Midland Core Research Center of Bureau of Economic Geology and in the core repository of The University of Texas of the Permian Basin. Currently, efforts are underway to describe the petrography of the carbonate parts of several of these cores and to build a modern depositional and sequence stratigraphic framework for the northwestern part of Permian Basin. The purpose of this research is to study Wolfcampian cores from five exploratory wells located on the Northwest Shelf and in southeastern New Mexico. The information obtained can then be applied in exploration for petroleum and provide valuable data for companies that are interested in exploring Wolfcampian carbonate deposits. Over ninety percent of the core is limestone, and only some zones are dolomitized. Despite karst diagenetic overprints, two types of cycles have been recognized from core examination. One type of cycle is a mud-dominated to grain-dominated skeletal capped packstone. Main skeletal grains in this cycle are fusulinids, broken fragments of crinoids, trilobites, brachiopods, and other unidentifiable skeletal fragments. Most of intraparticle porosity of the fusulinids has been filled with calcite cement and does not show good reservoir quality, and is less porous and permeable. However, heavy oil bits have been noted in some strata of the lower zones of this cycle. The other type of cycle is dominated by a peloidal, skeletal grain packstone, and is relatively porous and permeable. The data presented in this abstract is based on a preliminary examination of over two hundred feet of core and work is in progress. Further detailed examination of these cores, preparation of thin sections, and a detailed analysis of these cores should lead to a better understanding of Wolfcampian carbonate rocks in the study area.

AAPG Datapages/Search and Discovery Article #90190©AAPG Southwest Section Annual Convention, Midland, Texas, May 11-14, 2014