Exploration Implications of Oil and Natural Gas Seepage in Frontier Areas of the Louisiana-Texas Continental Slope, Northern Gulf of Mexico

Alan S. Kornacki, John W. Kendrick, John L. Berry

The occurrence, distribution, and chemistry of crude oil and natural gas seeps along the upper Louisiana continental slope have been used to help recognize and appraise the exploration potential of this frontier area. The presence of deepwater oil seeps was first established more than 25 years ago by the 'Eureka Program', a pioneering effort undertaken by Shell Oil Company that involved drilling coreholes above shallow salt bodies. Subsurface oil seeps were encountered at seven deepwater locations. Three Eureka seeps in the Green Canyon lease area occur downdip of oil discoveries at Bullwinkle and Vancouver. Even more intriguing, a cluster of subsurface oil seeps was identified on the south Texas continental slope in the Alaminos Canyon 970-971 blocks, 155 miles southwest of the nearest significant offshore oil production (at the Snapper Field).

Oil discoveries in water depths significantly >3000 ft have been reported only in the eastern Mississippi Canyon lease area. But oil and natural gas seepage is very common along the middle to lower Louisiana slope in the southern Garden Banks and north-eastern Keathley Canyon lease areas in water depths as great as 6000 ft, downdip of commercial petroleum discoveries at Auger, Bienville, and Cooper. These seeps demonstrate oil charge in a largely unexplored deepwater area off the coast of western Louisiana.

Other than proving regional charge, the presence of petroleum seeps near an untested deepwater prospect does not appear to materially aid in evaluating the likelihood that a commercial oil or gas accumulation exists in the subsurface. Prospect appraisal requires the performance of careful trap, seal, and reservoir analyses, plus an assessment of the vertical and lateral components of petroleum migration into the prospect.

AAPG Search and Discovery Article #91020©1995 AAPG Annual Convention, Houston, Texas, May 5-8, 1995