Hydrologic analysis of Gulf Coast-type geopressured zones

Conference · Tue Jan 01 04:00:00 EST 1985 · Geol. Soc. Am., Abstr. Programs; (United States)

OSTI ID:6577418

Bethke, C M

Hydrologic analysis of compaction-driven groundwater flow provides insights to the distributions and causes of geopressured zones in subsiding sedimentary basins, such as those found in the US Gulf Coast. Geopressured zones, subsurface areas of near-lithostatic fluid pressures, can localize petroleum reservoirs and economic mineralization, control sediment deformation, restrict groundwater circulation, cause problems in drilling, and may provide a future energy resource. Occurrences of geopressures are most frequently attributed to compaction disequilibrium caused by slow rates of fluid escape, aquathermal pressuring from thermal expansion of pore fluids, or the subsurface dehydration of smectite. The Lagrangian equation of compaction-flow, including effects of aquathermal pressuring and dehydration reactions, may be solved for the permeability profile required to maintain a lithostatic pressure gradient in a subsiding basin. Comparison of the closed-form solution with measured permeabilities shows that geopressured zones are likely to occur only in shaly or evaporite-rich basins which subside more rapidly than about 1 mm/yr. Solutions which consider fluid expansion alone give permeability values about two orders of magnitude less than those which only consider compaction, suggesting that aquathermal pressuring is much less important than compaction disequilibrium in causing geopressures. Solutions also show that of the likely contributions of smectite dehydration to geopressures, including release of structural water at depth, possible expansion of released fluids, and change in host rock permeability, the most important contribution is the observed decrease in shale permeability during dehydration.

• Research Organization: Univ. of Illinois, Urbana (USA)
• OSTI ID: 6577418
• Report Number(s): CONF-8510489-
• Conference Information: Journal Name: Geol. Soc. Am., Abstr. Programs; (United States) Journal Volume: 17
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
580100* -- Geology & Hydrology-- (-1989)
ENERGY SYSTEMS
FLUID FLOW
FLUID MECHANICS
GEOLOGIC STRUCTURES
GEOPRESSURED SYSTEMS
GROUND WATER
GULF COAST
HYDROGEN COMPOUNDS
HYDROLOGY
INTERSTITIAL WATER
MECHANICS
NORTH AMERICA
OXYGEN COMPOUNDS
PERMEABILITY
SEDIMENTARY BASINS
USA
WATER