ABSTRACT Recent Smackover fields discovered in the Central Mississippi Salt Basin can be characterized by their positions along the flanks of a series of northwest to southeast trending ridges. The majority of the Smackover production discovered in Mississippi during the 1960's and 1970's was in structural/stratigraphic traps associated with low relief anticlines. These discoveries were located along the basin margin and typified by such fields as Prairie Branch, Nancy, West Nancy, East Nancy and Pachuta Creek. Recent discoveries along the flanks of intermediate-size ridges indicate that significant additional Smackover reserves remain untapped. New and rejuvenated fields, such as West Chaparral, Clear Creek Tallabogue Creek, Shubuta and Winchester were located or extended by a combination of methods including deformation modeling, high quality, multi-fold seismic acquisition and interpretation and subsurface analysis of existing well control. Intermediate anticlines, as described by Hughes (1968), range in relief from 3500 to 7000 feet. Although each ridge exhibits a unique growth history, deformation styles and resultant fault patterns are similar from ridge to ridge. Many intermediate ridges have a dominant normal fault that is parallel or subparallel to the crest, and divides the ridge into upthrown and downthrown flanks. On the upthrown side the Smackover Formation has been uplifted by rapid movement during Haynesville deposition and, to a lesser extent, during Cotton Valley deposition. The Smackover Formation on the upthrown flank is truncated updip by the dominant ridge fault or by a subparallel buried fault. On the downthrown flank, Haynesville depositional loading has forced to flow laterally and vertically into the upthrown flank. As a result, the downthrown flank is structurally low due to withdrawal of underlying salt. The dominant normal fault, which transects the ridge, controls the shape of the feature. Yorsten (1989) describes these faults as downbuilding glide plane faults. On the downthrown flank of some ridges, a salt wall can develop along the plane of the dominant normal fault. Norphlet, Smackover and younger formations are successively truncated against the salt. The thickness of Jurassic strata juxtaposed to is dependent on the volume of transferred from the downthrown to the upthrown flank. On some intermediate sized ridges, compensation faults have developed on the downthrown flank, complicating the simple upthrown/downthrown model. Upthrown Smackover fields in Mississippi range in size from 100,000 to 10,000,000 barrels of oil and from one to ten wells. Many of the fields exhibit steep Smackover dips (10 to 50 degrees), thick pay columns and limited areal extent. Lateral and vertical seals are of critical importance in evaluating upthrown traps. Existing field evidence suggest that the best upthrown fields exhibit lateral and vertical reservoir seals formed by Lower Haynesville (Buckner) anhydrites. Relatively few downthrown Smackover fields have been exploited to date. West Chaparral Field, discovered in 1989, has made one million barrels of oil through December, 1991 from seven wells, and may ultimately produce five million barrels of oil. A generalized downthrown trap model shows the Smackover to be terminated updip by Louann Salt with the vertical seal provided by a thick Lower Haynesville section. Bed dips in the Smackover should be lower than those found in the upthrown trap due to the absence of late movement. Thick pay columns and larger closures may be expected in future downthrown fields as a result of excellent lateral and vertical reservoir seals and the lack of late structural movement. End_of_Record - Last_Page 851-------