FAULTS AND RESERVOIR COMPARTMENTALIZATION AT KUPARUK RIVER FIELD, ALASKA

The Kuparuk River field, located on Alaska’s North Slope, is the second largest oil field in North America. Since start-up in 1981, this field has produced over 2 billion barrels of oil from Cretaceous sandstones. 3D seismic interpretation reveals a high density of intra-reservoir faults, including over 6000 mapped at the full-field scale. Production data indicate that some faults are baffles or barriers. These faults subdivide the reservoir into hundreds of compartments, with uncertain flow connections. Economic production of remaining reserves requires accurate fault property prediction.

Over 30 years various approaches to fault characterization have had mixed success. Early efforts to derive simple predictive rules (fault strike, throw thresholds) failed. Detailed fault characterization has proven more successful, but time-consuming. Business needs have promoted an integration of multidisciplinary approaches to assigning fault properties that can be scaled to fit the area of investigation and number of faults in question.

Based on detailed studies, we have established relations between fault displacement, stratigraphic variation, reservoir flow units, and fault seal potential. These can be applied to individual faults or the entire field. A second approach derives fault properties from observed well interactions and from analysis of production and injection history. Rapid injector-producer response implies open faults; delayed or no response suggests faults that are baffles or barriers. A third method interprets the amplitude patterns seen in recent 3D seismic as a response to fluid saturations and/or reservoir pressure distribution. Contrasting amplitudes across faults suggest seal, and local amplitudes “spilling” through fault relays reveal leak points.

The integration of these three methods allows for the generation of new infill drilling opportunities and for a reduction of the associated risks, while greatly increasing the number of faults that have been characterized. Thus we have included more sophisticated fault properties in all stages of reservoir development planning, from screening for under-produced reserves to well planning to reservoir modeling. Recent drilling results support the integrated approach and provide additional feedback to the fault characterization.