Abstract

Twenty-five crude oil samples taken along strike, up and down dip, and stratigraphically high and low, along the 75-mile Abo reef trend in southeast New Mexico, were analysed chemically and isotopically. The objective was that these analyses would show significant relationships to geologic data and that conclusions might be made regarding source, migration, and accumulation of the oil.

The Abo reef trend is a narrow belt of dolomitized reef and bank carbonate approximately 75 miles long and one to three miles wide. These middle Permian rocks form the reservoirs for significant Abo fields such as Empire, Vacuum, Lovington, and Corbin. Dolomite of the Abo overlies Wolfcamp limestone. This interface is commonly used to separate rocks of Wolfcampian age from Leonardian age rocks; however, present evidence indicates that at least part of the subsurface Abo is Wolfcampian in age. The relationship of shelf, shelf-edge, foreshelf and basin exists in a north to south direction along the east-west trend. Generally, it can be stated that Abo hydrocarbons originated in the basin, migrated shelfward to the fore-shelf and shelf-edge and were restricted in further updip migration by anhydrite cement, caused by seepage refluxion occurring on the shelf, and extending with decreasing effect toward the basin.

The analyses showed that the crude oil taken from Permian Wolfcamp, Abo and Yeso reservoirs could have been derived from three major source groups: Abo-Wolfcamp basin rocks, Yeso basin rocks, and pre-Pennsylvanian rocks. It has been demonstrated that crude oil analyses along with carbon isotope analyses are useful tools that can be used to determine the age of the source rocks of the Abo oil and enable the geologist to make significant conclusions regarding origin, migration, and accumulation.