ABSTRACT

Upper Cotton Valley sandstones are gas productive in northeast Texas and northern Louisiana. The Frierson Field is a recently developed area that has a potential for significant gas reserves in the Davis, "B," and other sandstone members. The sandstones are interpreted as having been deposited as barrier bars that can be divided into three distinct facies based on vertical changes in texture, composition, and bedding. The facies are termed upper shoreface, middle shoreface, and lower shoreface and are similar to the modern Galveston Island barrier sequence.

The detrital composition of the Davis sandstones has an average of 86% quartz, and minor amounts of feldspars (1%), rock fragments (7%), and clay matrix (6%). These mineralogical components constitute 88% of the rock by bulk volume. The remaining 12% is primary porosity which has been occluded by 75% silica quartz overgrowth and 25% sparry calcite, each representing 9 and 3%, respectively, by bulk rock volume. Detrital composition ranges from 93% quartz in the upper shoreface, to 89% quartz in the middle shoreface, and to 76% quartz in the lower shoreface. "B" sandstones are also highly quartzose but have an average of 29% calcite matrix. Grain size decreases downward with the upper shoreface having a mean of 0.22 mm., the middle shoreface a mean of 0.14 mm., and the lower shoreface a mean of 0.10 mm.

Because the role of cementation is important with regard to the migration, accumulation, and storage of oil in a sandstone reservoir, the order of deposition of cementing materials in the sandstones was established as authigenic quartz overgrowths followed by authigenic calcite. The results of this study may be applicable to other areas of Cotton Valley deposition in northern Louisiana and northeast Texas.