Twenty-five crude-oil samples collected along strike, up- and downdip, and stratigraphically high and low along the 75-mi Abo reef trend in southeast New Mexico were analyzed chemically and isotopically. It was hoped that these analyses would show significant relationships with geologic phenomena and that conclusions might be made regarding source, migration, and accumulation.

Geologically the Abo reef trend is a narrow eastwest belt of middle Permian reef and bank-edge dolomitized carbonates approximately 70 mi long and 1-3 mi wide. These rocks form the reservoirs in significant Abo fields such as Empire, Vacuum, Lovington, etc. Dolomite of the Abo overlies Wolfcamp limestone. This dolomite-limestone interface is used commonly to separate rocks of Wolfcamp age from those of Leonard age; however, present evidence indicates that at least part of the subsurface Abo is Wolfcamp in age. The intertonguing relations of backreef, reef, forereef, and basinal facies exist throughout the extent of the east-west "reef" belt. Generally, it can be stated that Abo petroleum originated in the basinal facies, migrated to the forereef and reef facies, and was restricted fro further updip migration by anhydrite cementation. This cementation was caused by seepage refluxion on the shelf at the shelf-reef interface; anhydrite cementation decreases into the reef.

The analyses showed that the crude samples taken from Permian Wolfcamp, Abo, and Yeso reservoirs could be separated into three major source groups: Abo-Wolfcamp basinal rocks, Yeso basinal rocks, and pre-Pennsylvanian rocks. It has been demonstrated that crude-oil analyses and carbon-isotope analyses are excellent 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.

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