Abstract

The emerging Jurassic "salt wall" play in the Mississippi Salt Basin combines large structures, excellent seals, quality reservoirs, and prolific source rocks. Three large Smackover "salt wall" fields, Chaparral, North Clara, and West Chicora, have been discovered since 1989. North Clara (1993) and West Chicora (1998) are geopressured gas/condensate fields with high flow rates and estimated ultimate reserves of 100 billion cubic feet of gas equivalent. The Smackover "salt wall" play is being fueled by over 500 square miles of merged 3-D seismic data shot on a speculative basis between 1995 and 1999.

Intermediate and large salt anticlines are characterized by salt thicknesses ranging from 3,500 to 15,000 feet and lengths ranging from five miles to over 40 miles. Although each ridge exhibits a unique growth history, salt deformation styles and resultant fault patterns are similar from ridge to ridge.

The "salt wall" trap places upper Smackover reservoirs against Louann Salt, which serves as an effective lateral seal. The vertical seal is provided by Haynesville evaporites. Effectiveness of these seals is demonstrated by hydrocarbon columns in excess of 2,000 feet. The basal laminated member (lower) of the Smackover Formation is well documented as a world-class source rock. Hydrocarbons generated migrate into sealed Smackover reservoirs as an immature crude and crack in place during progressive burial.

Magnesium-rich Haynesville brines have extensively dolomitized portions of the upper Smackover, resulting in quality reservoirs with porosities as high as 25% and permeabilities of several hundred millidarcies. Although the Smackover remains the primary exploration target, the "salt wall" trap has also proved effective for Norphlet and Cotton Valley reservoirs.