Smackover Formation of Gulf Coast Region: ABSTRACT

Abstract

The Smackover Formation in the United States Gulf Coast region has been the target of continuing, and indeed renewed, exploratory interest of the oil industry. It is important that geologists understand the depositional and diagenetic realms that affected the Smackover, because of the influence they have on reservoir development. The Smackover was deposited during a major transgressive-regressive cycle. High-energy fossiliferous, pelletal, and oolitic grainstones deposited during the regressive End_Page 534------------------------------ phase form carbonate reservoirs that are widespread in Texas, Arkansas, Louisiana, Mississippi, Alabama, and Florida. Although much of the upper Smackover displays packstone and grainstone textures, there are variations in the type of allochems, percentage of micrite, and clastic sand content. For example, there are oolitic grainstones in the upper Smackover of east Texas, Arkansas, Louisiana, and southeastern Mississippi; micritic, pellet packstones are most common in parts of Alabama and the Florida panhandle; and deltaic, beach, and offshore-bar clastic sands are intermixed with carbonate beds in much of Mississippi. Of greater significance to the exploration geologist are variations in the amount and type of porosity within similar Smackover lithologies. These variations result from differences in diagenetic regimes. In Arkansas, Louisiana, and eastern Mississippi, the best reservoirs display incompletely cemented primary porosity. The preservation of porosity may be the result of early freshwater cementation, which occurred in areas that were uplifted and exposed during salt movement. Most of the updip Smackover carbonate grainstones contain leached moldic porosity, developed as extensive freshwater flushing occurred near the regional shoreline. Combinations of dolomitized intercrystalline and leached moldic porosity are prevalent in east Texas and Alabama-Florida. Dolomite porosity is less depe dent on early salt tectonics, although salt structures may still affect the shape of the productive reservoir. End_of_Article - Last_Page 535------------