ABSTRACT: A Higher Resolution Stratigraphic and Sedimentological Study of the Subsurface Queen City Formation (Eocene), Nacogdoches and Angelina Counties, Texas

Robert D. Garner, Harry H. Roberts

The Eocene Queen City Formation is a regressive fluvial-deltaic and shallow-marine depositional unit in the East Texas basin. Subsurface core and electric well log data are being used in a detailed subsurface stratigraphic study of the Queen City Formation in a portion of East Texas. Log data from approximately 250 wells across a seven county area of east Texas were used to produce stratigraphic cross sections plus structure, formation, and net sands isopach maps showing the regional structure and distribution of Queen City facies. Structure contour maps on the Formation top and base indicate progradation onto a gently sloping, structurally uniform shelf. Formation and net sand isopach maps reveal two lobate centers of deposition extending

basinward along southeast-trending depositional axes in Houston, Trinity, and Angelina Counties. These maps also indicate interval thicknesses greater than 200 feet in southwest Houston and Trinity Counties but thinning dramatically to the east and downdip to the southeast. Net sand thicknesses vary from greater than 100 ft proximal to the Formation "thicks" to less than 10 ft in the more distal areas.

Cores from producing fields in Angelina and Nacogdoches Counties are being used in a study of the sedimentology and depositional history of subsurface Queen City Facies. Previous studies were primarily based on well log data sets alone. Core studies indicate the Queen City Formation in this area is a dominantly fine-grained interval comprised of mudstones, siltstones, and very fine sandstones. Very thin (< 2 ft) sandstones and siltstones are generally located in the uppermost Queen City interval and are attractive shallow production targets. Thin section petrography, X-ray radiography, and SEM studies reveal Queen City and overlying Weches Formation sediments to contain abundant biogenic and diagenetic features. Vertical and horizontal burrows, shell material, glauconite and glauco ite cements, and diagenetic pyrite are common in the Weches Formation, which is interpreted as the product of shallow-marine shelf deposition characterized by slow deposition and extensive biogenic reworking. In contrast, the Queen City Formation reveals primary sedimentary structures and a general absence of bioturbation and extensive diagenetic features, which suggests rapid deposition and relatively high accumulation rates. These sediments are interpreted as representing the distal portion of a prograding deltaic wedge. This study is intended to provide a more precise qualitative and quantitative understanding of fine-grained Queen City reservoir materials as well as to identify optimal shallow producing trends based on a better stratigraphic interpretation of these subsurface facies. /P>

AAPG Search and Discovery Article #90999©1990 GCAGS and Gulf Coast Section SEPM Meeting, Lafayette, Louisiana, October 17-19, 1990