Permeability-porosity relationships of shallow mudstones in the Ursa Basin, northern deepwater Gulf of Mexico

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doi: 10.1029/2012JB009438
Author(s): Reece, Julia Schneider; Flemings, Peter B.; Dugan, Brandon; Long, Hui; Germaine, John T.
Author Affiliation(s): Primary:
Bureau of Economic Geology, Austin, TX, United States
Rice University, United States
ExxonMobil Upstream Research Company, United States
Massachusetts Institute of Technology, United States
Volume Title: Journal of Geophysical Research
Source: Journal of Geophysical Research, 117(B12). Publisher: American Geophysical Union, Washington, DC, United States. ISSN: 0148-0227
Note: In English. 22 refs.; illus., incl. sketch map
Summary: In the Ursa Basin, Gulf of Mexico, in situ mudstone permeability near the seafloor declines from 1.1 × 10-16 to 5.8 × 10-19 m2 over a depth of 578 m. We can reproduce this in situ permeability-porosity behavior through consolidation experiments in the laboratory. We use uniaxial constant-rate-of-strain consolidation experiments to measure permeability-porosity relationships and derive in situ permeabilities of 31 mudstone samples collected at Integrated Ocean Drilling Program (IODP) Sites U1324 and U1322. Although these mudstones have similar grain-size distributions, permeability at a given porosity varies significantly between the samples due to small variations in composition or fabric. We calculate an upscaled permeability relationship based on the observed permeability variation in the samples and determine a resultant large-scale permeability anisotropy of around 30. Based on this upscaled relationship and observations of in situ pressure, we calculate upward fluid flow rates of 0.5 mm/yr. We find that given the observed compressibility, permeability, and the geologic forcing at Ursa, overpressures are predicted as observed in the subsurface. The primary mechanism for overpressure generation at Ursa is sediment loading due to rapid burial. Low vertical permeabilities, accompanied by high sedimentation rates, can cause severe overpressure near the seafloor, which controls fluid flow and can reduce slope stability as observed in the Mississippi Canyon region. Such flow systems, especially at intermediate depths on passive margins, are important due to their control over macroscale behavior such as topographic gradient of continental slopes and submarine landslides, but have been largely understudied in the past.
Year of Publication: 2012
Research Program: IODP Integrated Ocean Drilling Program
Key Words: 06 Petrology, Sedimentary; 30 Engineering Geology; Atlantic Ocean; Clastic rocks; Expedition 308; Grain size; Gulf of Mexico; IODP Site U1322; IODP Site U1324; Integrated Ocean Drilling Program; Mudstone; North Atlantic; Permeability; Porosity; Rock mechanics; Sedimentary rocks; Size distribution; Textures; Uniaxial tests; Ursa Basin
Coordinates: N280600 N280600 W0890100 W0890200
N280500 N280500 W0890800 W0890800
Record ID: 2013063011
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