--> Depositional Interpretation and Sequence Stratigraphic Control on Reservoir Quality and Distribution in the Meramec STACK Play: Anadarko Basin, Oklahoma

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Depositional Interpretation and Sequence Stratigraphic Control on Reservoir Quality and Distribution in the Meramec STACK Play: Anadarko Basin, Oklahoma

Abstract

The Mississippian Meramec Stack Play is emerging as a premier unconventional target in Kingfisher, Blaine, and Canadian counties in the Anadarko Basin of west-central Oklahoma. It is dominantly a clastic system overlying more carbonate-rich Osagean intervals and Devonian Woodford Shale. Primary facies are composed of argillaceous to calcareous siltstones deposited in low energy conditions within or below storm wave base. Sediments were deposited as northeast-southwest elongate clinoforms with inclinations of less than 1 degree, prograding to the southeast. Low inclinations resulted in individual clinoforms forming in relatively similar water depths and energy conditions along depositional dip. These geometries and processes create strike-parallel facies belts through the play. The primary driver of reservoir quality in the Meramec is the percentage of calcite cement within individual facies. Large amounts of cement, occlude all effective porosity while lower volumes of calcite cement result higher porosity. Presence of clays is observed to inhibit cementation and preserve some primary porosity. These trends result in a strong depositional control on reservoir distribution as reservoir units are primarily deposited in low-energy settings below storm wave base with relatively higher volumes of clay, while non-reservoir is primarily higher energy facies deposited near or within storm wave base or in deeper settings by turbidite flows, with high initial depositional porosity that is preferentially cemented. The relationship between reservoir quality and changes in wave base creates a strong eustatic control on vertical segregation of reservoir and non-reservoir units on multiple scales. Mapping geometries and core facies stacking patterns indicate potential 3rd order sea level fluctuations control larger-scale abundance of reservoir and non-reservoir facies vertically through the section, while superimposed potential 4th order changes subdivide and control individual reservoir intervals. Integrated understanding of the overall sequence stratigraphic framework in concert with accurate depositional interpretation drives predictability of reservoir quality facies, aids in high-grading drilling locations and target intervals, and provides insight on play-wide stack potential as a function of sea level change.