ABSTRACT

Jolliet Field is believed to be the first development in the offshore U. S. Gulf of Mexico to exploit a major thrust fault structure and, as such, represents a new and potentially important type of deep-water structural play. The field's multiple, stacked reservoirs consist of Pleistocene lowstand gravity flows deposited in upper slope fans. The thrust fault is documented by 3-D seismic interpretation, repeated paleontologic markers, and correlation of up to 3000 feet of repeated pay section. This fault is believed to be the toe thrust of a major gravity slide which was triggered in the Lower Pleistocene when sediments were tilted to a critical angle by a rising salt diapir. Seismic data suggest that the resulting slide surface is approximately cylindrical, connecting a major growth fault on the west side of Green Canyon Block 184 to the Jolliet Field thrust fault. Salt withdrawal in the area produced normal faults, some of which cut the thrust fault, adding structural complexity to the field. In addition to the geologic and geophysical evidence, the structural model is supported by slope stability computer modelling using realistic sediment shear strengths, densities, and pore pressures.