Depositional interpretation and sequence stratigraphic control on reservoir quality and distribution in the Meramecian STACK play, Anadarko Basin, Oklahoma, USA

The Mississippian Meramecian play in the greater STACK (Sooner trend Anadarko Basin, Canadian and Kingfisher Counties) play region is an unconventional reservoir in the Anadarko Basin in west central Oklahoma. The play is a fine-grained system composed of quartz silt and sand with varying amounts of carbonate grains and clay. The primary driver of reservoir quality is the quantity of calcite cement. Large volumes of cement are found in coarser grained higher energy facies whereas porosity is preserved in lower energy facies, imparting a strong depositional control on reservoir quality. The play interval comprises a system of deep-water prograding parasequences striking northeast-southwest and prograding to the southeast. Inclinations of clinoforms are less than one degree. Depositional conditions are inferred to be similar along strike, resulting in northeast to southwest facies continuity. The depositional interpretation of this system is a subaqueous delta. These are systems of low-angle, shore-parallel clinoforms fed by fluvial input reworked primarily by longshore currents within or below storm wave base. Core and log analyses indicate the play is a lowstand clastic wedge deposited during early sea-level rise. It is bounded by a sequence boundary and correlative conformity at its base and capped by a transgressive surface of marine erosion. An intermediate order sea-level rise-fall-rise occurs during overall deepening. High order sea-level changes are manifested as stacked parasequences grading upward from argillaceous and quartz siltstones into calcareous siltstones to sandstones. The identified sequence stratigraphic hierarchy imparts a threefold control on reservoir and nonreservoir architecture, as it drives the volume and distribution of porous and nonporous facies at differing scales.