Integration of Geology and Reservoir Engineering to Produce Reservoir Simulation Model at Cabin Creek Field, Cedar Creek Anticline, Montana

Ron Pieterson, Michael J. Dimarco, and Sandra S. Sodersten

Because of its mature stage of development, a key aspect of continued economic development of the Cedar Creek Anticline (CCA), Montana (STOOIP > 2 billion barrels with over 360 MMstb produced) is the identification of remaining pods of high S₀ within the original field boundaries. Present economic conditions make it essential to select drillsites with high prnbabilities of success and high prognosed flow rates in these remaining high S₀ area. Integration of a well-constrained geologic model and reservoir simulation pinpointed remaining pods of oil in a 3-m thick, subvertically fractured, dolomitic limestone reservoir of the Carboniferous Mission Canyon Formation in the Cabin Creek Field of the CCA. This resulted in a successful high-flow-rate hori ontal well (initial rate >800 BOPD) whose oil production was accurately predicted by a 3-D reservoir simulation. The 3D model layers coincide with the geologic sub-zones 1, 2 and 3 of the Mission Canyon 5 Formation. In addition, two aquifer layers were attached to simulate bottom water encroachment in this natural water-drive reservoir. The model has 53,750 gridblocks each of which is 60 by 60 m. The effect of the natural-fracture network was constrained with the k_v/k_h (vertical to horizontal permeability ratio). The simulation covered a 40-yr. production period. Gross production was input as a constraint; oil and water rates were matched. Adjustments to absolute permeability, aquifer volume and relative water permeability were required to obtain a match between bserved and simulated production rates. The model was fine tuned by matching the production of individual wells in areas with a high remaining S₀. This entailed adjustments to transmissibility, k_v/k_h, and the contributions of sub-zones. In some cases, significant adjustments of k_v/k_h were necessary. This project demonstrated that (1) interplay of geology and reservoir engineering provided a better reservoir model than could have been done individually, (2) simulation work identified horizontal drilllng and recompletion candidates, with one successful horizontal well completed to date, and (3) use of the reservoir simulator for field-scale modeling in conjunction with a well-refined geologic synthesis can successfully pinpoint undevel ped reserves at CCA.

AAPG Search and Discover Article #91019©1996 AAPG Convention and Exhibition 19-22 May 1996, San Diego, California