Abstract

This stratigraphic study of South Arkansas and North Louisiana demonstrates the existence of at least four progradational calcarenite rock bodies or banks within the Smackover Formation of Jurassic Age. Each bank was deposited approximately parallel to the ancestral Gulf shoreline and basinward of the next older bank. All of these banks are major reservoirs for oil and gas pools.

Prior to 1960, the Reynolds oolite of the Smackover Formation of South Arkansas was correlated with the Smackover “B” oolite of North Louisiana. The absence of anticlines with structural closure and the paucity of untested fault-closures along the Arkansas-Louisiana state boundary produced little exploratory interest in the area. Discovery of oil at Lick Creek Field in 1960 and at Walker Creek in 1968 revealed a trend of traps and led to the geological investigation that resulted in the discovery in 1972 of Chalybeat Springs Field located in Columbia County, Arkansas.

Chalybeat Springs Field is a combination stratigraphic-structural trap in oolitic calcarenite at a depth of 10,250 feet in the Smackover “B” Limestone. Updip the production is limited by the combination of a tilted anticline with a porosity pinchout on its flank. The field originally had 29 producing wells and 10 dry holes and covered approximately 4,500 productive acres. Original oil in place is estimated to have been 37 million barrels and cumulative production through 1985 was approximately 12 million barrels.

The geologic relationships observed in the Smackover Limestone of South Arkansas and North Louisiana can and have been successfully applied to other regions and in different aged carbonate strata in the geologic search for oil and gas fields.

Practical geologic studies of carbonate rocks aided by examination of drill cuttings and thin sections result in lower finding costs for oil and gas reserves.