Characterizing Faults and Predicting Seal Behavior from Kuparuk Field, Alaska
The Kuparuk River field, located on Alaska’s North Slope, is the second largest oil field in North America. Discovered in 1969, with start-up in 1981, this field has produced over 2 billion barrels of oil from lower Cretaceous sandstones. 3D seismic interpretation reveals a high density of intra-reservoir faults, including over 6000 mapped at the full-field scale. Both pre- and post-production data indicate that some faults are baffles or barriers. Key challenges at Kuparuk include maximizing reserves depletion while managing operating costs. Fault characterization and predicting reservoir compartmentalization are critical to accessing the remaining resource and value.
Over the past 20 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 efforts have 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 and lab tests of core samples, we have established relations between fault displacement, lateral stratigraphic variation, 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 detailed 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 3D seismic as a response to fluid saturations and/or to reservoir pressure distribution. Thus contrasting amplitudes across faults suggest seal, and local amplitudes “spilling” through fault relays reveal lateral leak points.
The integration of these three methods allows for the generation of new infill opportunities and for a reduction of the associated risks and uncertainties, 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 supports the integrated approach and provides additional feedback to the fault characterization.
AAPG Search and Discovery Article #90090©2009 AAPG Annual Convention and Exhibition, Denver, Colorado, June 7-10, 2009