The amount of oil that is contained in the Canadian oil sands represent the third largest oil accumulation in the world. Approximately half of the daily oil production from the oil sands comes from mining processes and the other half is produced mostly using steam assisted gravity drainage (SAGD). This method is effective at reducing the viscosity of the oil. However, the generation of steam requires a significant amount of energy. Thus, there is an ongoing effort to reduce the energy needed to produce oil from the oil sands. In this article the intermittent injection of a solvent, along with steam, is investigated as a means of reducing the amount of energy required to extract oil from the Canadian oil sands. A simulation-based study examined the effect of the type of solvent, the cycles’ duration, the solvent concentration and the number of cycles. The simulations covered a time span of 10 years during which several different solvents (methane, ethane, propane, butane, pentane, hexane, and CO2) were injected under varying injection schedules. The solvents that were investigated are compounds that are likely to be readily available at a heavy oil production site. The solvent injection periods ranged from six to 24 months in length. The results reveal that SAGD combined with intermittent injection of hexane resulted in the most significant improvement to the cumulative oil production and in the cumulative energy-oil ratio (cEOR). Compared to SAGD without solvent injection, the cumulative oil production was increased by 45% and the cEOR was reduced by 23%. It was also seen that the performance of the proposed process is highly dependent on the resulting physical properties of the solvent-bitumen mixture. Finally, a simplified economic analysis also identified SAGD with intermittent hexane injection as the scheme that resulted in the highest net present value. Compared to SAGD without solvent injection, the intermittent injection of hexane led to an 85% increase in the net present value.
Approximately half of the daily oil production from the Canadian oil sands comes from the application of steam assisted gravity drainage (SAGD). Due to the high steam requirements of SAGD, many studies have focused on solvent injection as a means of reducing the steam consumption. One of the multiple variations of the steam-solvent injection process consists on the intermittent co-injection of solvent with steam, also known as a cyclic expanding-solvent (ES)-SAGD process. The current study represents a first attempt to create an analytical model that can describe a cyclic ES-SAGD process. The proposed analytical model uses previous SAGD and ES-SAGD models to describe the steam plus solvent stages of the process. The results obtained from the analytical model were contrasted against numerical simulation results for cases in which the solvent was hexane, pentane, and butane, as well as for cases in which hexane is a solvent and the injection cycle length is variable. In all cases, it was seen that the cumulative oil production computed by the analytical model and the numerical model are in good agreement. Over the range of conditions that were tested the absolute relative difference in the cumulative oil production, after a period of 10 years, ranged from 8.6% to 9.4%, with a median value of 9%. However, compared to the numerical simulations, the analytical model did not fully match the oil rate and the steam chamber shape. This difference was attributed to the analytical model’s simplified description of heat and mass transfer during the process. Thus, it is recommended that further studies be conducted, and recommendations for further investigations are given.
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