Faults as Barrier/conduit Systems in Oil Migration

The sealing nature of faults has been well documented in numerous compacting rift basins such as the Gulf of Mexico and the Niger Delta. However, thermal and salinity anomalies observed along faults suggest that they can also act as vertical conduits for fluid flow. We investigate the three-dimensional, conduit-barrier nature of faults in extensional basins. We place particular emphasis on the analysis of oil migration in overpressured basins using a new finite element model RIFT3D. We carried out a sensitivity study in which fault throw, sedimentary layer thickness, clay content, and fault block geometry are systematically varied. Fault slip rate, strata thickness and clay content are used to update hydraulic properties of the fault zones over time following the approach of Bense and Person (2006). Results indicate that in general faults, act as barriers to lateral, cross-fault flow while being conduits for along- fault flow. However, cross-fault flow and oil migration can occur when a reservoir is juxtaposed to a permeable unit on the other side of the fault and under conditions of intermediate fault zone clay content. Buoyancy pressure generated by oil column can also help to push through barriers created by fault and migrate in faulted basin.