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Fault Impact on Reservoir Performance: A Synthetic Case Study of Host Rock Sand Lenses in Fault Cores

Niclas Fredman1, Jan Tveranger1, Siv Semshaug1, Alvar Braathen1, and Einar Sverdrup2
1 Center for Integrated Petroleum Research, Unifob, University of Bergen, Bergen, Norway
2 Roxar Software Solutions, Oslo, Norway

We present a synthetic study on fault impact in siliciclastic reservoirs using a volumetrically defined fault.

Normally, simulation models of faulted reservoirs include faults as grid offset in combination with transmissibility coefficients. This approach tends to ignore the actual 3D architecture of fault zones commonly seen in seismic scale faults. Representing faults as 3D rock volumes in reservoir models may capture effects which are presently overlooked and possibly yield a more realistic description of the structural heterogeneities.

An experimental, synthetic 3D model with a single normal fault was constructed by defining a fine grid around the fault plane. The fault grid was subsequently populated with two conceptual fault rock types; host rock sand lenses and fault gouge. The fault gouge permeability and host rock sand lens permeability were systematically varied between 0.01-1 mD and 50-500 mD, respectively. A total of 480 realizations were generated and flow simulated.

Simulation results show, among other results: (i) host rock sand lenses in contact with undeformed host rock can constitute an important flow path through faults, especially when the fault gouge matrix permeability is low. (ii) As the fault gouge matrix permeability is increased towards 1 mD, the host rock lenses become less important as flow paths and the fault gouge matrix permeability is becoming more important. (iii) Host rock lenses not in contact with undeformed host rock do not appear to affect fluid flow significantly.