Abstract

The present Oil Study Committee of the West Texas Geological Society was organized to study the oil composition and related stratigraphy of six projects in the Permian Basin. These projects include the Simpson, Pennsylvanian and Wolfcamp, Abo, Delaware and Yeso rock units and the Multipay field study. Crude oil and associated water samples were analysed by the Bureau of Mines Petroleum Research Center at Bartlesville, Oklahoma. Carbon isotope data were provided by Sinclair Oil & Gas Company, Tulsa, Oklahoma.

Oil samples were distilled and the gasoline and gas-oil part determined. The volume percent of paraffins (straight or branched chains), aromatics, and naphthenes (ring compounds) was derived for boiling fractions 1-7 (gasoline) and also of the aromatics for fractions 8-12 (gas-oil). The carbon isotopic composition was determined for the high boiling fraction (+350°F). This composition is a function of the type of organic material deposited, the environment of deposition, and the maturation history of the organic material. Data from recent sediments show an increasing δC¹³ isotopic composition extending from rocks deposited in the terrestrial environment through those deposited in the open-marine, marine-carbonate and marine-evaporite environments. Water samples were analysed for pH, specific gravity, calcium, magnesium, sulphate, chloride, sodium and resistivity.

Analytical data, including aromatic and naphthene profiles, were used to group the oils based on elements of similarity. These groups were compared with isotopic composition and associated water data. Interpretation was based on the geologic history of the rock units involved in each project.