Medium/heavy oils are successfully waterflooded in the Lloydminster region of Alberta. Two major areas are Wainwright and Wildmere. This paper gives an explanation as to how and why those waterfloods work well and the insights gained from a theory of fractal flow. Oil is gradually "wrung" out of the formation while water is circulated for some pressure support but primarily for gas saturation control. Injection water is quite dirty and plugs the formation. Induced fracture networks allow the formation to simultaneously filter the input water and dispose of the filtrate, a procedure which would otherwise be quite costly. Differences between fractal flow and frontal displacement are discussed along with the various mechanisms of pressure support, gas saturation control, mixed phase flow, imbibition and emulsification. Conclusions are drawn which include expected pressures, errors and special care required in voidage calculations. A schematic analogue of the life history of the injection/production interchange and suggestions for well and pattern conversions are also made. In difficult economic times, optimizing current production by altering the pressure gradients in the reservoir can yield a good return.

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