--> Abstract: Fluid Expulsion from Abnormally Pressured Strata along Growth Faults in the Eugene Island Block 331 Area, Gulf Of Mexico, by P. B. Flemings, L. L. Alexander, M. Spiegelman, and R. N. Anderson; #91012 (1992).

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ABSTRACT: Fluid Expulsion from Abnormally Pressured Strata along Growth Faults in the Eugene Island Block 331 Area, Gulf Of Mexico

FLEMINGS, PETER B., Lamont-Doherty Geological Observatory, Palisades, NY, LAUREL L. ALEXANDER, Cornell University, Ithaca, NY, and MARC SPIEGELMAN and ROGER N. ANDERSON, Lamont-Doherty Geological Obserratory, Palisades, NY

Perturbed temperature and pressure fields along a north-south cross section in the Eugene Island Block 331 area indicate that focused fluid flow may be occurring along or adjacent to basin-bounding growth faults. The transition with depth to pressures greater than hydrostatic (geopressures) is illustrated with contour maps of mud weight data. We define soft geopressures at 12 lb/gal (~0.65 psi/ft), hard geopressures at 15 Ib/gal (~0.75 psi/ft), and the vertical distance between the two as the geopressure transition. In the hanging wall, soft geopressures reach depths up to 8000 ft and the geopressure transition is as wide as 4000 ft. The transition zone rises 3500 ft and is compressed to a width of 2000 ft as it approaches the basin-bounding fault. In the foot wall, soft geopressuring occurs at shallow levels but the transition zone widens again away from the fault to ~4000 ft. Isotherms, defined by bottom-hole temperatures, reveal a temperature anomaly with ~500 ft of relief in the hanging wall immediately above the basin-bounding fault. The anomaly coincides with the compressed geopressure surfaces and is greatest in the transition zone. Above the transition zone, the temperature anomaly decreases and becomes more diffuse.

Pleistocene strata in this area are regressive, changing upward through the section from bathyal shales and basin-floor fan deposits to inner-neritic deposits which range in age from Lenticulina-1 time (~2.2 Ma) to present. Growth faulting (down to the south) occurred synchronously with deposition of fan deposits in the hanging wall, resulting in more than 3500 ft of vertical displacement. The pressure and temperature data, when combined with the stratigraphy and timing of faulting, imply that geopressured fan sediments in the hanging wall are releasing fluids laterally toward the basin-bounding faults. These fluids are then carried upward, through the low permeability geopressured strata, where they are dispersed into more permeable, normally pressured, rocks above.

 

AAPG Search and Discovery Article #91012©1992 AAPG Annual Meeting, Calgary, Alberta, Canada, June 22-25, 1992 (2009)