Geologic Observations of the Whirlpool Sandstone in Western Warren County, Pennsylvania
ENSIGN, JAKE, Quaker State Corporation, Pleasantville, PA
The Whirlpool Sandstone represents the lowest member of the Lower Silurian Medina Group. The sandstone is ubiquitous in western New York and northwestern Pennsylvania, but economic development is difficult to predict and locate on a consistent basis. This reservoir appears to be composed of a basal beach sand, which in some areas is overlain by what appears to be a prograding tidal/channel facies.
Gross sequence of strata maps and unique vertical-profile maps have been helpful in reconstructing the depositional history of this reservoir. Porosity-foot maps have been very helpful for most development drilling decisions. Detailed cross sections have also provided valuable insight regarding subtle, but important, structural trends.
Sonic logs and QLA2 logging software have helped to accurately determine that the cementation exponent is lower than 2.0, which is thought to be characteristic of intergranular porosity. This has justified recompletions in some areas where the Whirlpool was originally not completed due to overly pessimistic water saturations. Dipmeter data have further confirmed the existence of two separate depositional environments. Enhanced vertical resolution of logging information has increased the accuracy of data used for mapping and statistical review.
A multiple regression equation has been used to identify those parameters possessing the highest degree of correlation when compared to reserves. The maximum value for r-squared (correlation coefficient) was 0.66. The equation-generated reserves were compared against decline-curve reserves and the results were extremely close, suggesting that the regression equation could be used to predict lifetime reserves even before the well is completed. However, since the independent variables are geographically sensitive, this equation can be used only in very specific areas.
AAPG Search and Discovery Article #91005 © 1991 Eastern Section Meeting, Pittsburgh, Pennsylvania, September 8-10, 1991 (2009)