Regional Stratigraphy of Smackover Limestone (Jurassic) in South Arkansas and North Louisiana, and Geology of Chalybeat Springs Oil Field

A. R. Troell, J. D. Robinson

This stratigraphic and structural study of oil fields in south Arkansas and north Louisiana demonstrates the existence of at least four progradational calcarenite rock bodies or banks within the Jurassic Smackover Formation. Each bank was deposited approximately parallel with the ancestral Gulf of Mexico 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 boundary provided 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 geologic investigation that resulted in the discovery, in 1972, of Chalybeat Springs field, in Columbia County, Arkansas.

Chalybeat Springs field is a combination stratigraphic-structural trap in oolitic calcarenite at a depth of 10,250 ft in the Smackover "B" limestone. Production is limited by the combination of a tilted anticline with porosity pinch-out on its flank. The field originally had 28 producing wells and 10 dry holes, and covered approximately 4,500 productive acres. Original oil in place is estimated to have been 37 million bbl and cumulative production through 1985 was approximately 12 million bbl.

The geologic relationships and principles observed in the Smackover Limestone of south Arkansas and north Louisiana have been successfully applied to other regions and in carbonate strata of different age, in the search for oil and gas production.

Practical geologic studies of carbonate rocks, aided by examination of drill cuttings, cores, and thin sections, combined with mechanical log evaluations, result in lower finding costs for oil and gas reserves.

AAPG Search and Discovery Article #91042©1987 GCAGS and GC-SEPM Section Meeting, San Antonio, Texas, October 28-31, 1987.