Reservoir Characterization of Upper Devonian Gordon Sandstone , Jacksonburg , Stringtown Oil Field

The Jacksonburg-Stringtown field was discovered in 1895. It is located on the western flank of the Burchfield syncline, in southeastern Wetzel, eastern Tyler, and northwestern Doddridge counties, West Virginia. Over 500 wells were drilled in the field between 1 897 and 190 1 ; most were plugged by 19 10. Primary recovery has been estimated to lie between 1454 and 1590 barrels of oil per acre. Primary production was a result of solution gas drive and gravity drainage through the mid-1920's and resulted in production of an estimated 13 million barrels of oil. Gas injection began prior to the 1940's. Recovery attributed to gas injection averaged 154 BOPA over a limited portion of the field. The pilot waterflood of the Gordon was installed in 198 1 as an approximately 34 acre dual five-spot. Since 1990, more than 100 new wells have been drilled for water injection and 40 new wells drilled for production. Between January, 1991 and February, 1999, 1,864,782 barrels of oil have been produced as a result of the full-scale waterflood. Three statistically significant, positive correlations involving Permeability is significantly correlated with primary porosity, secondary porosity, and potassium feldspar content. Potassium feldspar grains weather relatively easily into clay, leaving intergranular porosity and hence, permeability. Potassium feldspar content is positively correlated with both secondary porosity and clay content. Four Electrofacies identified in the Gordon are: Electrofacies 1 , corresponding to shales within the Gordon; Electrofacies 2 and 3, corresponding to Non-Pay Sandstones (sandstones of Electrofacies 3 are coarser that 2); and Electrofacies 4, corresponding to Pay Sandstones of the reservoir. Conglomerates are found interbedded with the sandstones of Electrofacies 3 and 4. In vertical crosssection, Electrofacies 3 and 4 are observed to be asymmetrically distributed within the Gordon Reservoir and to be concentrated on the east side of the field. Lithology and sedimentary structures observed in outcrop are similar to features observed in Non-Pay sandstones in the reservoir. Consequently, the minimal permeabilities measured in outcrop are analogous to those in the Non-Pay sandstones in the Gordon. The outcrops as a whole cannot be used as a model of the Pay sandstones in the reservoir. A relationship between core plug permeability values, mini-perms, and geophysical well log data was developed through an Artificial Neural Network. Permeability was predicted with R-squared values greater than 76% with the exception of one well. Redefinition of flow units improved simulation results in the pilot area. Flow unit I consisted of the lower part of the conglomerate-sandstone sequence and the upper part of the sandstone section. This Flow Unit has a slightly lower porosity but much lower permeability. Flow unit I1 is defined as the lower part of the sandstone. It has higher porosity and permeability.