Numerical-Simulation Investigation of the Effect of Heavy-Oil Viscosity on the Performance of Hydrocarbon Additives in SAGD

Heavy oil and bitumen are expected to become increasingly important sources of fuel in the coming decades. There are extensive deposits in Alberta that could be a principal source of fuel in the coming century. The Athabasca oil sands, the largest petroleum accumulation in the world: the Cold Lake oil deposit; and the Lloydminster reservoir are all major Canadian oil-sands deposits. Steam-assisted gravity drainage (SAGD), which has shown considerable promise in all three of these major deposits, remains an expensive technique and requires large energy input. The energy intensity of SAGD and the environmental concerns make it imperative to find new oil-extraction technologies. Coinjecting hydrocarbon additives with steam offers the potential of lower energy and water consumption and reduced greenhouse-gas emission by improving the oil rates and recoveries. In a previous paper by the same authors (Hosseininejad Mohebati et al. 2010), we showed that the selection of a suitable hydrocarbon additive and the effectiveness of this hybrid process are strongly dependent on the operating conditions, reservoir-fluid composition, the heavy-oil viscosity, and the petrophysical properties of the reservoir. Among these factors, the heavy-oil viscosity, which is the main difference between these three reservoirs, could be a very important parameter in the performance of this hybrid process. Therefore, it is necessary to optimize the hydrocarbon additives to SAGD for these three oil-sand deposits separately. Extensive numerical studies in a 3D model by means of a fully implicit thermal simulator were conducted to evaluate the efficiency of each hydrocarbon additive with different heavy-oil viscosities (resembling those of Athabasca bitumen, Cold Lake heavy oil, and Lloydminster heavy oil). Varying mole percents of hexane, butane, and methane were coinjected with steam to each reservoir with different heavy-oil viscosity. The optimum amount of hydrocarbon injection was reported in each case. This culminated in a novel method for selecting the most advantageous hydrocarbon additive and its optimum concentration considering the heavy-oil viscosity.