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Overview of pore pressure in the Anadarko Basin
Philip Nelson1, Nicholas Gianoutsos2
1United States Geological Survey, 2United States Geological Survey
Petroleum reservoirs of the Anadarko Basin extend broadly over western Oklahoma, the Texas and Oklahoma panhandles, and southwestern Kansas. Pre-production pressure data from drillstem tests, mud weights, and bottom-hole estimates are examined for this large area utilizing pressure-depth plots, and geologic maps and cross-sections. A compilation of these data combined with observations from previous publications reveals three areas distinguished by their pressure signatures. The first area lies in the basin proper, with a normally pressured regime extending to about 10,000 ft in depth that is underlain by one or two stepped increases in pressure; pressure gradients are as high as 0.9 psi/ft. The high-pressure volumes were previously mapped as cogent mega-compartments. The second area lies on the north flank of the basin, where, from east to west, overpressured units grade into normally pressured strata without any clear geologic control on the transition. Resistivity and sonic logs indicate that both presently overpressured and normally pressured rocks were overpressured at some time in the geologic past. The third area occupies the Texas and Oklahoma panhandles and southwestern Kansas, where underpressured strata extend to depths of 10,000 ft. This area includes the productive Hugoton gas fields in rocks of Permian age, for which the pressure reference is posited to be in hydraulic communication with an exposed aquifer in eastern Kansas. The goal of this study of pressure distribution is to achieve a better understanding of fluid flow at the time of hydrocarbon generation and its relation to basin structure.
AAPG Search and Discover Article #90097 © 2009 Tulsa Geological Society, Tulsa, Oklahoma
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