Waterflood Optimization of the Buffalo Coulee Bakken Heavy Oil Pool of Southwestern Saskatchewan

Abstract

Abstract Since 1969, a waterflood scheme has been implemented in the Bakken sand heavy oil reservoir in the Buffalo Coulee field of southwestern Saskatchewan. Even with 20-acre well spacing in the waterflood area located in section 22-32-24 W3M, projections of oil recovery appear to be low, especially in the northern half of the section where much of the original gas cap still exists. Reservoir simulation was employed to investigate the potential of well spacing reduction from 20-acre to 10-acre by infill drilling, the merit of additional water injection into the reservoir, and the effect of gas cap blowdown on oil recovery. A reservoir model representing section 22 and the surrounding waterflood area was calibrated by history matching the historical production and injection performance of the 48 wells in the study area. Based on history match results, the shale layer between the oil pay and the gas cap provides a vertical permeability barrier in the gas cap area of the reservoir. This was confirmed by the findings of a recently drilled well where injected water was found to have completely flushed the gas cap, resulting in water currently situated on top of the oil zone in that portion of the reservoir. Based on performance predictions conducted on the calibrated reservoir model, the current 20-acre well spacing is adequate for the waterflood scheme in the pool, since infill drilling with either vertical or horizontal wells will not recover any significant incremental oil reserves. Furthermore, blowing down about 14.9 × 106 m3 of gas from the gas cap will have no detrimental effect on the estimated oil recovery of about 18% of the original oil-in-place (OOIP), based on current water Injection rates in section 22. If water injection in section 22 is increased by about 50%, oil recovery from section 22 can be improved to about 22% of the OOIP, corresponding to an incremental oil recovery of about 76,000 m3, or 4% of the OOIP. Introduction The Buffalo Coulee Bakken Sand Pool is located approximately 7 kilometres northwest of Coleville, Saskatchewan (Figure 1). The discovery well, 21/7-22-32-24 W3M, was drilled in August, 1952. The pool covers sections 15, 16, 21, 22 and 23-32-24 W3M. Independent Energy Inc. ("Independent") is the operator for 21 and 22, while Dan oil Energy Ltd. is the sections 15 and 23. P. 369