Diagenesis, Diagenetic Banding, and Porosity Evolution of the Middle Ordovician St. Peter Sandstone and Glenwood Formation in the Michigan Basin
Peter A. Drzewiecki, J. Antonio Simo, P. E. Brown, E. Castrogiovanni, Gregory C. Nadon, Lisa D. Shepherd, J. W. Valley, M. R. Vandrey, B. L. Winter, D. A. Barnes, 1994. "Diagenesis, Diagenetic Banding, and Porosity Evolution of the Middle Ordovician St. Peter Sandstone and Glenwood Formation in the Michigan Basin", Basin Compartments and Seals, Peter J. Ortoleva
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The Middle Ordovician St. Peter Sandstone and Glenwood Formation of the Michigan basin are composed of alternating intervals of quartz sandstone, micritic carbonate, and an occasional thin shale. They contain abnormally pressured compartments in the deepest portion of the basin. Some of these pressure compartments are gas reservoirs and are bounded, above and below, by diagenetically banded sandstone and/or carbonate sedimentary units.
Diagenetically banded sandstones are dominated by bands of quartz cement that formed as a result of chemical compaction, quartz dissolution, and quartz precipitation during burial. Petrographic and geochemical data suggest that quartz overgrowths precipitated from fluids with a slight meteoric component. Dolomite, the second most abundant authigenic mineral in diagenetic bands and elsewhere in the St. Peter and Glenwood, postdated quartz overgrowths and precipitated from hypersaline fluids at high temperatures. Values of 513C from the dolomite indicate that the carbon was partially derived from the maturation of organic matter, and the carbon isotopic composition appears to be stratigraphically controlled. Bands of dolomite and quartz cement occur in horizontal and cross-bedded siliciclastic lithofacies that contain planar depositional discontinuities, such as grain size laminations.
Original porosity in the St. Peter Sandstone and Glenwood Formation was relatively homogeneous within a given lithofacies. Diagenesis, especially the development of diagenetic bands, resulted in heterogeneous porosity distribution. The porosity was reduced to 0 to 3% in the tightly cemented bands (quartz and dolomite) and in intervals that experienced intense intergranular pressure solution. The most significant porosity modification occurred in the deep burial environment. Depositional controls on diagenesis include bedding style, degree of bioturbation, and original mineralogical composition of the sediments. The correlation between depositional facies and diagenetic banding may allow regions of low porosity and permeability to be predicted within a sequence stratigraphic framework in deeply buried sandstones.
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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.