Reservoir Analysis and Simulation of an Oil Pool with a Leaky Fault

Abstract Oil production from the Cecil Lake North Pine C pool in northeast British Columbia started in 1972. Due to the sand dune depositional environment, the reservoir has well sorted sand grains resulting in high permeability rock. The C pool directly offsets the larger Cecil Lake North Pine A pool to the north, separated only by a fault with a throw of about 40 meters. Pressure, depletion and material balance analyses clearly indicated flow communication between the A and C pools through what has to be a leaky fault. It was then necessary to include both oil pools in the geological modeling and reservoir simulation work. To allow flow communication, connections were established between the grid blocks on the fault edge of both pools. Based on the validated composite simulation model of both pools, it was found that incremental oil reserves can be realized from the C pool by providing energy support through down-dip water injection. However, this development scenario was deemed uneconomic due to the remoteness of the water source in the field and the challenging topography for laying the necessary water injection pipelines. Introduction The Cecil Lake North Pine A and C Pools are located in township 84, range 17 and township 84, range 18, West of the 6th meridian, just north of the Fort St. John Graben (Figures 1 and 2). Separated by a fault from the A pool, the C pool currently has a low oil recovery factor of about 12% OOIP. Therefore, a reservoir simulation study was conducted to gain a better understanding of its upside potential. Several C pool development scenarios were evaluated such as initiating a water injection scheme, further drilling of infill wells and blowing down the gas cap. Geological Overview The Cecil Lake North Pine A and C pools are separated by a normal fault trending northeast to southwest based on interpretation of available seismic data. The throw on this fault is approximately 40 meters as illustrated by the top North Pine porosity structure map (Figure 3). Previous geochemical work by Reidiger et al suggests that the source of the hydrocarbons in the Charlie Lake is the phosphate zone of the Doig and that the hydrocarbons migrated along vertical faults and fractures that cut through the impermeable dolostone, mudstone, siltstone and anhydrite zones of the Charlie Lake.(2) The North Pine Member of the Upper Triassic Charlie Lake Formation, part of the Schooler Creek Group, consists of a fine to medium grained, moderately to well sorted and well rounded, calcareous quartz sandstone and cryptocrystalline anhydrite. This zone is up to four meters in thickness, and approximately 650 meters below sea level in the Cecil Lake Area (Figure 4). The North Pine is interpreted to be an erosional remnant of an Aeolian dune field, deposited within a sabkha and lagoonal environment as part of a barrier island complex.(1) The Cecil Lake North Pine sandstone averages 2 – 4 meters in gross thickness with an average net pay of approximately 2.0 meters (Figure 5).

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