Faulting and fault sealing in the TAGI Formation of the Ourhoud Field, Algeria

Little is known about the nature of faults that cut the Triassic Argilo-Greseux Inferieur reservoir of the Berkine Basin, Algeria. To rectify this, an analysis was performed of faults in the Ourhoud Field in terms of their geometry, connectivity and fault sealing potential. Different oil-water contacts had been identified across the field, suggesting a degree of fault compartmentalization. Fault-rock material from cored wells in the Ourhoud Field was analysed to determine the type, permeability and capillary threshold pressure. The suite of fault rock present is highly varied, ranging from disaggregation faults and cataclasites in clean sands to clay smears. All the fault rocks have lower permeabilities and higher capillary threshold pressures than the undeformed host rock of the Triassic Argilo-Greseux Inferieur. The observed oil-water contact and pressure differences can all be supported by the dominant fault rocks if their clay content exceeds 20%. Fault-rock data were also used to generate transmissibility multipliers for incorporation into the Ourhoud geological and simulation models. Significant reductions in transmissibility multiplier are generated by more clay-rich fault rocks separating reservoir units with permeabilities ranging from 10 mD to 1000 mD.