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Stratigraphic Architecture, Facies Distribution, and Reservoir Characteristics of the Colony Granite Wash, Anadarko Basin, Oklahoma


The Pennsylvanian Granite Wash of the Anadarko Basin was deposited over a large area as a series of alluvial fans to fan deltas and deepwater deposits composed of clastic and carbonate sediments and detritus eroded from the uplifted Amarillo-Wichita ancient mountain front. For the Desmoinesian-age Colony Granite Wash, located in Washita and Custer counties, Oklahoma, deposits exhibit a complex stratigraphic architecture along a proximal-to-distal transect (south to north into the basin) with highly variable lithofacies and associated reservoir-rock properties. The stratigraphic, sedimentologic, and reservoir characteristics of the Colony Granite Wash are established based on cores, thin sections, well logs, and 3-D seismic data. The Colony Granite Wash consists of three sandstone-rich stratigraphic intervals (A, B and C) that are each bounded by laterally extensive shales and associated marine-flooding surfaces. The shales are recognizable in core and on well logs and are useful for correlation. Detailed core descriptions and well-log characteristics show that the Colony Granite Wash varies from proximal deposits consisting of chaotic conglomeratic debris flows that are highly discontinuous to laterally continuous distal flows displaying cyclic turbidite successions. The dominant lithofacies include calcareous and non-calcareous sandy upward-fining debris flows and calcareous and non-calcareous shales. The producing lithofacies, non-calcareous sandy debris flows, exhibit porosity values that range from 5% to 10.5% and permeability values that vary from 0.003 to 0.02 mD. Wireline-log response is calibrated to detailed lithofacies descriptions from core to establish a rock-type model and to estimate lithology/lithofacies logs in non-cored wells. The lithology and porosity logs are used to condition 3D facies and porosity models of the Granite Wash that show the impact of the stratigraphic architecture and lithofacies distribution on petrophysical properties and associated reserves.