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Overpressure Development Through Time Using 4-D PVT Modeling in the Deep Anadarko Basin, Colorado, Kansas, Oklahoma and Texas


A 4-D petroleum system model of the Anadarko Basin of southeast Colorado, western Kansas, northeast Texas, and Oklahoma was built to evaluate pressure development and petroleum generation, migration, and accumulation through time. This pressure-volume-temperature (PVT) model incorporates 3D Darcy flow to replicate fluid flow and pressure evolution. Modeled Mississippian and Pennsylvanian strata are currently overpressured in an area of the deep Anadarko Basin of Oklahoma and Texas. This pressure compartmentalization is mainly present in Morrowan through lower Virgilian strata. Overpressure began 305 million years ago (Ma) within the Mississippian and Pennsylvanian Morrowan layers in the 4D model. This was primarily the result of disequilibrium compaction from (1) rapid burial of strata in the deep basin through the Mississippian and Pennsylvanian, (2) internal seals that include Morrowan and Atokan mudstone lithofacies, (3) underlying and overlying seals of the Devonian-Mississippian Woodford Shale and (4) Missourian-Virgilian shales; these shales also form permeability barriers at the lateral termination of overpressured strata. Strata below the Woodford Shale were not overpressured through time, probably because sedimentation of these strata was gradual enough for pressure to equilibrate. Overpressured strata in the basin form a wedge that pinches out along the east and west boundaries and thins from south to north. Overpressure was probably enhanced as a result of oil and gas generation and expulsion from petroleum source rocks in the deep basin, as indicated by paleopressure and overpressure being enclosed within the Woodford Shale layer oil- and gas-generation boundaries. Overpressure and oil generation from the Woodford Shale was contemporaneous.