The Banded Character of Pressure Seals
Pressure seals in the Anadarko basin contain distinct diagenetic bands that play a significant role in the isolation of high-pressure domains. Both sand-rich and clay-rich clastic rocks exhibit banding patterns. Banding in sandstones results primarily from the processes of pressure solution, pore-fluid interaction, and precipitation. Some banding patterns in clay-rich rocks appear to form independently of sedimentary textures while others result from the enhancement or modification of sedimentary features. All of these bands are noticeably absent in rocks that were never buried deeply enough to be overpressured.
Diagenetic bands in sandstones 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 suggesta mechanism for the derivation of silica cements.
Diagenetic bands in clay-rich rocks appear to have two distinctly different origins. In the Pink/Red Fork interval, diagenetic chlorite bands exhibit no apparent relationship to sedimentary features. The chlorite bands have less porosity and smaller pore-aperture radii than the surrounding shale (Powers, 1991). In the Woodford Shale, silica- and clay-rich bands develop via the diagenetic modification or enhancement of sedimentary features.
Figures & Tables
Basin Compartments and Seals
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.