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Few heavy oil reservoirs with strong bottom water drives have been developed successfully because of severe water coning. Water coning tends to cause low ultimate recovery, low well productivity, and high water production. Although thermal and gravity-assisted methods might improve recovery in oil reservoirs, such methods are widely perceived as either economically unfavorable or technologically infeasible. This study proposes a new, cold production technique, called Bilateral Water Sink (BWS), to meet those challenges. The BWS method suppresses water cresting by producing oil and water simultaneously from separate, horizontal wells completed in the oil and water zones; the oil and water completions are parallel, with the oil well directly above the water well. In conventional horizontal well production, water cresting causes water to bypass oil, making the water drive mechanism ineffective. BWS controls water invasion by altering the pressure distribution in the near-well area. With cresting suppressed, the oil completion remains water-free, allowing water to displace oil from the edges of the well drainage area to the oil completion, increasing ultimate recovery. Unlike existing heavy oil recovery methods, BWS exploits the natural reservoir energy in the bottom water drive. This makes BWS economically, technically, and environmentally appealing especially for offshore applications, where cold production is currently the only option and oil-water separation is a problem. In this study, BWS oil recovery is investigated analytically and numerically. A new mathematical model identifies controlling variables and project design parameters, and describes the relationships among them. The design model is used to select rates of water and oil in BWS wells for best performance. The analytical model is verified by a comparison to numerical simulations. These two approaches together provide the quantitative account of the BWSs effect on avoiding water cresting and improving oil recovery. The results show that BWS can increase oil recovery from 10 percent to over 40 percent in a conventional case, while avoiding the problem of oil-contaminated water production. As a result, the mathematical model of BWS well behavior is shown to be a practical reservoir management tool to guide development of heavy oil reservoirs with bottom water drives. |
