AN INTEGRATED SEDIMENTOLOGY, RESERVOIR QUALITY AND HYDROCARBON SOURCE ROCK ASSESSMENT OF THE PENNSYLVANIAN MIDDLE HOXBAR GROUP IN THE ANADARKO AND MARIETTA BASINS, OKLAHOMA

The Pennsylvanian (Missourian Series) Hoxbar Group in the Anadarko Basin is a prolific producer of oil and gas. Within this clastic interval the most prominent reservoirs include the Wade and underlying Medrano, Marchand, and Culp sandstones. The depositional environment and the relationships among these sandstones and related interbedded shales are poorly understood. The Medrano sandstones and interbedded mudstones are interpreted to be part of a tidally-reworked deltaic/shallow marine system. Similarly, the Marchand sandstone is interpreted to be part of a tidally dominated shoreface system with localized channeling. Hoxbar cores from the southern flank of the Marietta Basin display fining upward successions indicative of fluvial point bar deposition. Bioturbation ranges from low diversity (only Chondrites and Planolites) zones in pro-delta lithologies to very diverse, high bioturbation-index zones in lithologies deposited within shoreface environments.

The average grain sizes of these sandstones range from silt to medium sand. Common allochems include pelecypod, brachiopod and crinoidal fragments. Kaolinite vermicules are noted in some of pores and have considerable microporosity. Electron microprobe analysis of K-feldspars, the width of perthite intergrowths and modal composition of sandstones indicate a source of alkali granite rocks that are present in the Wichita Mountains in southern Oklahoma.

Hydrocarbon distribution patterns and formation water analysis indicate faults and unconformities form the boundaries of reservoir compartments. Additionally, paleobathymetry and differential compaction of the underlying strata has led to thinning and thickening of sandstone deposits. Molecular and isotope analyses of oils from 16 Hoxbar wells in Grady County indicate that the underlying Woodford Shale is the most likely dominant hydrocarbon source with minor petroleum contributions from Pennsylvanian organic mudstones. This study utilized an integrated approached providing insights into the origin of the sediments, depositional processes, tectonic history/paleogeography, diagenesis and potential sources of hydrocarbons.