KORNACKI, ALAN S., Shell Offshore Inc., New Orleans, LA, HENRY I. HALPERN, Saudi Aramco, Dhahran, Saudi Arabia, and GARY S. STEFFANS, Shell Internationale B. V. Petroleum Mij., The Hague, Netherlands

ABSTRACT: Petroleum Source Potential of Miocene and Eocene Shales from the Continental Slope of the Northwestern Gulf of Mexico

From 1965 through 1968, 80 core holes were drilled by the M/V Eureka above shallow salt bodies on the continental slope of the northwestern Gulf of Mexico (offshore Texas and Louisiana) in water depths of 660-5280 ft. (An additional 13 deep-water core holes were drilled in the north-central Gulf of Mexico.) Approximately 40,000 ft of sediment and small amounts of diapiric salt and/or associated cap rock were penetrated by these 80 Eureka core holes, from which more than 18,000 ft of core subsequently was recovered. Although most core holes penetrated only Pleistocene sediments, allochthonous sequences of older sediments (Pliocene-Upper Cretaceous) emplaced during salt diapirism were penetrated at eight drill sites in the northwestern Gulf of Mexico.

We have determined the petroleum source potential of Miocene and Eocene shales from four deep-water Eureka core holes (water depths of 1890-2350 ft) in the northwestern Gulf of Mexico. All of these samples have attained only moderate levels of thermal maturity (VR (approx.) 0.4-0.6). Two samples of Miocene shale obtained from the East Breaks 672 Block are relatively lean (containing only 0.37-0.54 wt.% total organic carbon), and their kerogen is enriched in gas-prone or inert macerals. Eocene shales penetrated in the Alaminos Canyon 970 and 971 blocks are slightly richer (0.68-0.95 wt.% total organic carbon), principally because they contain migrated petroleum -- aliquots extracted with a strong organic solvent contain only 0.31-0.48 wt.% total organic carbon. The leanest sample is an Eocene shale obtained from the boundary between the Garden Banks 332 and 333 blocks, approximately 18 mi northwest of the deep-water Auger oil and gas discovery. This sample contains only 0.33 wt.% total organic carbon, and its kerogen also consists predominantly of gas-prone or inert macerals. Thus, we conclude that these Tertiary shale samples are not the source of the oil that has been generated in the deep-water realm of the northwestern Gulf of Mexico.

AAPG Search and Discovery Article #90989©1993 GCAGS and Gulf Coast SEPM 43rd Annual Meeting, Shreveport, Louisiana, October 20-22, 1993.