GENERATION OF OVERPRESSURE AND COMPACTION-DRIVEN FLUID-FLOW IN A PLIOPLEISTOCENE GROWTH-FAULTED BASIN, EUGENE ISLAND 330, OFFSHORE LOUISIANA

The complex pressure and porosity fields observed in the Eugene Island (EI) 330 field (offshore Louisiana) are thought to result from sedime nt loading of low-permeability strata. In this field, fluid pressures rise with depth from hydrostatic to nearly lithostatic, iso-pressure s urfaces closely follow stratigraphic surfaces which are sharply offset by growth-faulting, and porosity declines with effective stress. A on e-dimensional hydrodynamic model simulates the evolution of pressure a nd porosity in this system. If reversible (elastic) compaction is assu med, sediment loading is the dominant source of overpressure (94%). If irreversible (inelastic) compaction and permeability reduction due to clay diagenesis are assumed, then thermal expansion of pore fluids an d clay dehydration provide a significant component of overpressure ( > 20%). The model is applied to wells on the upthrown and downthrown si des of the major growth fault in the EI 330 field. Assuming that sedim ent loading is the only pressure source and that permeability is a fun ction of lithology and porosity, the observed pressure and porosity pr ofiles are reproduced. Observation and theory support a conceptual mod el where hydrodynamic evolution is intimately tied to the structural a nd stratigraphic evolution of this progradational deltaic system.