Quantitative analysis of slip-induced dilation with application to fault zone fluid migration

A new quantitative model for calculating the amount of fluid migration during fault slip is developed. This model is based on observations from laboratory rock mechanics experiments of porosity evolution during frictional sliding and geophysical data that demonstrate the existence of propagating slip pulses that experience transient dilation during earthquakes. The nature of dilation during slip is dependent on the frictional behavior, that is whether the fault experiences seismic or aseismic slip. The transient dilation that occurs during seismic slip is more efficient in transporting fluids along the fault than the semi-permanent, but relatively reduced dilation that occurs during aseismic slip. For aseismic faults, fluid migration rates are primarily dependent on the existing (static) permeability structure of the fault rock. For the seismic case, both the static and dynamic (i.e, during seismic slip) permeability are important. Applications of these models to estimate leakage using fault parameters derived from seismically active faults that trap hydrocarbons in the Cuisiana Field, Columbia, and aseismic faults at Eugene Island Block 330 Field, Gulf of Mexico, are grossly consistent with observed hydrocarbon volumes and inferred along-fault migration rates. Results of this model have broad implications for understanding the effects of faults on charge/migration, compartmentalization, and providing permeable pathways for the leakage of reservoir fluids on exploration (geologic) and production time scales.