Generation of overpressure and compaction-driven fluid flow in a Plio-Pleistocene 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 sediment loading of low-permeability strata. In this field, fluid pressures rise with depth from hydrostatic to nearly lithostatic, iso-pressure surfaces closely follow stratigraphic surfaces which are sharply offset by growth-faulting, and porosity declines with effective stress. A one-dimensional hydrodynamic model simulates the evolution of pressure and porosity in this system. If reversible (elastic) compaction is assumed, 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 and clay dehydration provide a significant component of overpressure (>20%). The model is applied to wells on the upthrown and downthrown sides of the major growth fault in the EI 330 field. Assuming that sediment loading is the only pressure source and that permeability is a function of lithology and porosity, the observed pressure and porosity profiles are reproduced. Observation and theory support a conceptual model where hydrodynamic evolution is intimately tied to the structural and stratigraphic evolution of this progradational deltaic system.