Megacompartment Complex in the Anadarko Basin: A Completely Sealed Overpressured Phenomenon
Zuhair Al-Shaieb, James O. Puckette, Azhari A. Abdalla, Patrick B. Ely, 1994. "Megacompartment Complex in the Anadarko Basin: A Completely Sealed Overpressured Phenomenon", Basin Compartments and Seals, Peter J. Ortoleva
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Integrated pore pressure, potentiometric, and geologic data in the Anadarko basin demonstrate the existence of a basin wide, completely sealed overpressured compartment, called the megacompartment complex. All reservoirs within this complex exhibit pressure gradients that exceed the normal gradient of 10.515 kPa/m (0.465 psi/ft). These reservoirs have produced large quantities of natural gas, particularly from the Pennsylvanian Red Fork and Morrowan sandstones.
This megacompartment complex is enclosed by top, basal, and lateral seals. The top seal zone, which is located between 2290 m and 3050 m (7500 and 10,000 ft) below the surface, is relatively horizontal, dips slightly to the southwest, and appears to cut across stratigraphy. However, the diageneticide enhanced basal seal is stratigraphically controlled and seems to coincide with the Devonian Woodford Shale. The complex is laterally sealed to the south by a vertical cementation zone associated with the frontal fault zone of the Wichita Mountain uplift and by the convergence of the top and basal seals along the eastern, northern, and western boundaries.
The interior of the complex is subdivided into a myriad of smaller compartments with distinct pressure gradients. In addition, local overpressured compartments are present outside the megacompartment complex in normally and near-normally pressured regions.
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Basins worldwide exhibit an unexpected degree of hydrologic segregation. There can be regions of a sedimentary basin that are isolated from their surroundings by a relatively thin envelope of low-permeability rock with an interior of sufficiently high permeability to maintain a consistent internal hydrostatic fluid pressure gradient. These have been named pressure compartments. Presure compartments have several remarkable features, just one of which is that internal fluid pressures can greatly exceed or be significantly less than any regional topographically controlled hydrologic head or drain. This publication contains 30 chapters that take detailed looks at pressure compartments in general, and detail case studies of these compartments in specific basins, such as the Anadarko and Gulf of Mexico. The volume also looks at other considerations in sedimentary basins such as hydrodynamic and thermal characteristics, and mechanical properties of rock.