Fault-Plane Reflections as a Diagnostic of Pressure Differences in Reservoirs - South Eugene Island, Offshore Louisiana

Seismic data taken at Blocks 314, 315, 330, and 331 of the South Eugene Island field contain reflections from a major growth fault. Out of a list of possible causes, we find that differences in pore pressure across the fault give rise to the fault-plane reflections over a large portion of the fault. The pressure differences are detectable since pore pressures that exceed the hydrostatic pressure, or overpressures, lower the seismic velocity. Thus, the presence of the fault-plane reflections point to the fault providing a significant lateral seal. We develop a processing scheme to highlight the fault-plane reflections while simultaneously removing the reflections from the layered structure. Using this processed data set, we extract the amplitude of the fault-plane reflections on the fault-plane. The areas of strong reflection amplitude correlate well with the geology and known zones of overpressure. Over a limited area on the fault, we observe reflectivity originating fiom elevated pore pressures in the fault zone itself.