An Integrated Approach to Refining Reservoir Description Through Monitoring Fluid Movements in the Prudhoe Bay Reservoir

Abstract

Accurate reservoir description significantly enhances the ability to assess reservoir performance and to predict future performance from simulation and analytical techniques. These predictions impact infill drilling, waterflood area selection and operation, production offtake strategies, well completions, and workover philosophy. An integrated approach that uses available production and surveillance data has been employed to refine reservoir description. The available data includes: open and cased hole log data, reservoir pressure and transient analysis interpretations, RFT pressure data, and individual well production histories. Downdip production from beneath continuous shale complexes has resulted in lateral movement of gas from the original gas cap at Prudhoe Bay. This and other physical evidence of barriers to vertical flow have been used to calibrate and enhance confidence in geologic shale maps based on well to well correlations. In areas where vertical gas cap expansion has occurred, tracking reservoir fluid movements has provided a method to identify the occurrence and observe the drainage of oil lenses from discontinuous shales. In addition, the data has allowed the computation of volumetric sweep efficiencies to improve reserve estimates, and delineate areas where recoveries can be increased by adjustments to offtake strategy, or application of future improved oil recovery techniques.