Field Measurements of Low Energy Oil Sands Mobility

Abstract The bitumen contained in Axe Lake Discovery in Saskatchewan has very high viscosity, well over 10 million centipoises under original reservoir condition. Since bitumen viscosity decreases with increasing temperature even at low temperatures, and since the Axe Lake reservoir is highly permeable and extremely coarse grained, preliminary reservoir simulations indicated that it is possible that effective, early time, communication between production wells at the bottom of the reservoir can be established by efficient low energy heating and intermittent water pressure pulsing. In order to evaluate the heating concept, we measured the response of the reservoir to heating with down-hole heaters at low temperatures (100 °C). A description of the field test is provided. Different analytical formulations and simulation models were used to analyze the results of the field test and the analyses were compared to prior published work. Field results were also used to determine effective thermal conductivities and effective mobilities at low temperatures for different grid sizes using Cartesian, radial and hybrid simulation grids. A comparison to analytical heat transfer formulations under different boundary conditions is discussed. Calibrated simulations show that not only can the heater be used to preheat the formation but also as an efficient bitumen viscosity reduction tool to increase bitumen mobility during the full bitumen production life of the reservoir. Moreover, high temperature heaters can be combined with cold water injection to generate steam in the reservoir directly. The paper concludes with a simple analysis which shows that such a combined technology can produce bitumen more efficiently and economically when compared to conventional SAGD. Introduction Axe Lake Discovery is located in northwestern Saskatchewan, about 90 km northeast of Fort McMurray. The bitumen reservoirs are buried about 200m below the surface. The bitumen is quite heavy and highly viscous, with a viscosity of over 10 million centipoises at original reservoir condition. Since bitumen viscosity decreases when the temperature rises, thermal technologies such as steam and hot water injection have become the preferred means for bitumen recovery. However, the bitumen reservoir at Axe Lake is relatively shallow and the efficient recovery of bitumen may be not possible using high pressure steam and hot water injection. Preliminary reservoir simulations indicated that it is possible to establish effective communication between producers at early time by efficient low energy heating and intermittent water pressure pulsing. Measuring the response of the reservoir to heating with downhole heaters at low temperature 100 °C, a two-stage test was planned and the second stage is currently being implemented. Different analytical formulations and simulation models were used to analyze the results of the measurement. The effective thermal conductivity and mobility of the bitumen at low temperature will be obtained from the results. Simulation studies also indicated that it was possible to obtain bitumen recovery effectively and economically using high temperature down-hole heater combined with cold water injection. This method takes advantage of simple and safe surface facilities and without losing heat outside the wells when compared to conventional steam injection from the surface.