|Granite Wash, Palo Duro Basin, Texas
After reviewing the pressure-data analyses presented by Orr and others (1985), we chose to use 0.403 psi/ft as the slope of the pressure function for the deep brine aquifer (Granite Wash) of the Palo Duro Basin. We chose this value because it derives from the most consistent data ("Class A") presented by Orr and others (1985). They defined "Class A" pressure data as those values for which both initial and final shut-in pressures were available and that agreed within 10 percent. The original data came from drill-stem tests of petroleum exploration wells. Orr and others (1985) obtained them from Petroleum Information Service, Inc. Note that this value, 0.403 psi/ft, is below the estimated hydrostatic gradient of deep-basin brines, 0.466 psi/ft. By choosing only the "Class A" data of Orr and others, we hope to eliminate one possible reason for the underpressuring of the saline aquifer, poor-quality drill-stem tests. Therefore, according to Orr and others, there are two other possible reasons for this underpressuring: (1) isolation from shallower, hydrostatically pressured aquifers or (2) potential for downward flow within the aquifer. Orr and others presented evidence for both cases in the deep brine aquifer of the Palo Duro Basin.
Orr, E. D, Kreitler, C. W., and Senger, R. K., 1985, Investigation of the underpressuring in the deep-brine aquifer, Palo Duro Basin, Texas: The University of Texas at Austin, Bureau of Economic Geology, Geological Circular 85-1, 44 p.