ABSTRACT:

Present models that predict pore pressure and structural style of critical tapers all assume constant values for the friction angle and the slope of the compression curve for mudrocks in these tapers. Experimental studies, however, show that these parameters both decrease significantly with stress level over large stress ranges encountered in these tapers (e.g., up to 100 MPa). We modify present analytical models to accommodate these behaviors and use the modified models for mudrocks from Eugene Island, Gulf of Mexico, to quantitatively illustrate the impacts of these stress-level-dependent behaviors on pore pressure and structural style of critical tapers. We demonstrate that the stress-level decrease of the friction angle causes a concave-upward topography, a concave-downward profile for thrust faults, and lower overpressure in critical tapers. In contrast, the stress-level decrease of the slope of the compression curve causes a higher overpressure in upper sediments and a lower overpressure in lower sediments of these tapers.

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