REQUARTH, JEFFREY S., JOHN J. MORRIS, and MARCUS A. BRANDON , Savannah Oil and Gas, L.L.C., Houston, TX

The emerging Jurassic "salt wall" play of the Mississippi Salt Basin combines large structures, excellent seals, quality reservoirs and prolific source rocks. Three large Smackover salt wall fields, West Chaparral, North Clara and West Chicora, have been discovered since 1989. North Clara (1993) and West Chicora (1998) are pressured gascondensate 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 data shot on a speculative basis by CGG between 1995 and 1999.

Intermediate and large salt anticlines, as described by Hughes (1968), range in salt thickness from 3,500 to 15,000 feet. The length of salt ridges varies 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 efficient lateral seal. The vertical seal is provided by Haynesville evaporites. This quality seal configuration can result in hydrocarbon columns in excess of 2,000 feet. The Brown-Dense Member (Lower) of the Smackover Formation is well documented as a world-class source rock (Klemme and Ulmishek, 1991). Brown-Dense generated hydrocarbons migrate into sealed Smackover reservoirs as an immature crude and crack in place with burial.

Magnesium rich Haynesville brines have completely dolomitized portions of the Upper Smackover resulting in high quality reservoirs with porosities of up to 25% and permeabilities reaching 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.

AAPG Search and Discovery Article #90908©2000 GCAGS, Houston, Texas