Modeling Faults as Conduit-Barrier Systems to Fluid Flow in Siliciclastic Sedimentary Reservoirs

Bense, Victor, Mark Person, Indiana University, Bloomington, IN

Faults can act as barriers to horizontal fluid flow and compartmentalize pore fluids in hydrocarbon reservoirs and shallower aquifer systems. However, the same fault systems can also form preferential pathways for vertical flow. This is evidenced by geothermal anom­alies, fault hosted ore deposits, and preferential oil migration via faults. We propose that this enigmatic behavior of faults could be caused by a strong hydraulic anisotropy in the fault plane. This anisotropy results from clay-smearing, dragging of sand, and grain re-orienta-tion. We propose a new algorithm to predict fault width, lithological heterogeneity, and hydraulic anisotropy from fault throw and the clay content of the lithologies flanking the fault zone. Example simulations of reservoir and sedimentary basin scale flow systems indicates that permeability perpendicular to the fault plane is up to four orders of magnitude lower than in the direction parallel to the fault plane. We found that fault zone hydraulic anisotropy had a profound effect on fluid flow paths, temperature patterns, and age distribution of flu­ids around in and around the fault zone.