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Oklahoma State University, Stillwater, OK

Abstract: Compartmentalization of the Overpressured Interval in the Anadarko Basin

Reservoir pressures within the lithologic column in the Anadarko basin are a tiered system. The overpressured zone called the Mega-Compartment Complex (MCC) is overlain and underlain by normally pressured intervals. Compartments are classified in three different groups or levels. The basinwide MCC is called a Level 1 compartment. Within the MCC, reservoirs that form fields or districts commonly have similar pressure values. These fields or districts are called Level 2 compartments. Detailed analyses of initial pressure, fluid types and decline curves indicate that Level 1 and 2 compartments contain many smaller and isolated (sealed) compartments called Level 3 type. The seals occur mainly in clay- or sandrich rocks and commonly exhibit diagenetic banding patterns.

Banding patterns in clay-rich rocks appear to form independently of sedimentary textures or result from the enhancement or modification of sedimentary features. Diagenetic bands in sandstones typically consist of silica- and carbonate-cemented layers that are separated by clay-coated porous layers. Stylolites and other pressure-solution features such as penetrating grain boundaries suggest a mechanism for the source of silica cements. The integration of tectonic history, stratigraphic relationships, facies distribution, thermal history, and diagenetic patterns of seal zones suggests that seals and compartments evolved primarily during the Pennsylvanian orogenic episode. This occurred during the rapid subsidence phase of the orogeny over a period of approximately 30 million years.

AAPG Search and Discovery Article #90921©1999 AAPG Mid-Continent Section Meeting, Wichita, Kansas