Controls on Hydrocarbon Entrapment and Reservoir Distribution: The Pennsylvanian Oswego Limestone and Big Lime Limestone in the Putnam Field Area, Anadarko Basin, Oklahoma

James R. Geary¹ and Stacy Atchley^2
1 Anadarko Petroleum, Houston, TX
² Baylor University, Waco, TX

Putnam Field, located along the northern margin of the Anadarko Basin and extending through Custer and Dewey counties in western Oklahoma, USA, has produced over 400 BCF and 13 MMBO from the Pennsylvanian (Desmoinesian) Oswego Limestone and Big Lime. Hydrocarbons are stratigraphically trapped within phylloid algal mound complexes that are isolated within shallowing-upward parasequence sets; mound complexes generally trend west-east across the study area parallel to the northern structural margin of the Anadarko Basin. Reservoir quality within phylloid algal mounds is controlled by variations in the abundance of moldic, vugular, and fracture pore types (average porosity = 2%, median permeability = 0.2 md). Eleven parasequence sets occur within the study interval and from the section base to top stack progradationally within the Oswego Limestone, and aggradationally to retrogradationally within the overlying Big Lime. The change from progradational to retrogradational stacking of parasequence sets most likely reflects an accelerating rate of subsidence during deposition that was induced by thrust-loading along the Ouachita foldbelt. Furthermore, retrogradational stacking within the Big Lime suggests that undiscovered hydrocarbon reserves may exist updip (northward) of the Putnam Trend in slightly younger deposits. Detailed maps of structure, facies, gross pay, and pore volume were generated for each parasequence set, and compared with the spatial distribution of producing wells and their associated drainage radii. From these attributes, a geologic risk assessment was completed across the Putnam Trend to determine the most prospective areas for future step-out development.

AAPG Search and Discovery Article #90039©2005 AAPG Calgary, Alberta, June 16-19, 2005