PETERSEN, LEE, and BOB LUNN
Anadarko Petroleum, Houston, TX

Abstract: Gulf of Mexico Subsalt Exploration: A Fifteen-Year Look

With the advent of Gulf of Mexico area-wide leasing in 1983, exploration for deepwater deposited siliciclastic sandstones under allochthonous salt masses has become a tantalizing target for industry activity. Forty-three wells have been spud with subsalt sedimentary packages as the primary objective. This activity has resulted in thirteen discoveries, nine of which are considered commercial. Within the overall exploratory history of the Gulf of Mexico, the subsalt play is early in its life cycle. Industry interest in subsalt exploration reached its peak in late 1993 through early 1994 with the discoveries of Mahogany and Enchilada. During this time period, a 50% exploratory success rate was achieved. Success continued in late 1995 and early 1996 with exploratory tests at Gemini and Agate, but increased drilling costs and a perception that advancement in below salt imaging techniques was not as rapid as originally thought began to erode industry's confidence in the viability of the play. Single exploratory wells reached a cost of $40 million or more. In addition, during the last eight months of 1996, eight exploratory wells were drilled without a commercial discovery. These factors, in conjunction with industry's reaction to the United States government's royalty relief bill in deep water, pushed industry's attention to the deep water. Exploration of the subsalt continued at a ten exploratory well per year pace in 1996 and 1997, but industry's attention was already focused on the Gulf of Mexico deep water.

The fundamentals of the subsalt play in the Gulf of Mexico are sound. With the discovery at Eugene Island 344, 345, 346 (Tanzanite) during 1998, industry success stands at 35%. Rigorous work to support reservoir-prone fairways, reconstruct salt movement and improve seismic imaging needs to continue if future subsalt exploratory potential is to be realized.

AAPG Search and Discovery Article #90928©1999 AAPG Annual Convention, San Antonio, Texas