Steam-Solvent Process: A Gamechanger in Cutting Emissions in In-Situ Recovery of Oil Sands

Due to extensive energy requirements and the volume of emitted greenhouse gases associated with burning natural gas to generate steam in the SAGD process, there has been always a strong motivation to develop oil recovery processes for bitumen reservoirs with lower energy and emissions intensities. A hybrid steam-solvent co-injection process, which is to synergize the advantages of both SAGD and VAPEX processes and minimize their drawbacks is the subject of ongoing research and field piloting since early 2000. Most of the past efforts of the steam-solvent process were primarily focused on improving the oil rate or improving the process's economic benefits. However, due to Canada's ambitious greenhouse emission reduction target (net zero emission by 2050) along with the significant increase of carbon tax ($170 by 2030), the primary focus of the oil industry is shifting towards reducing steam injection and cutting the GHG emission drastically. This study revisited the steam-solvent process to find a suitable combination of solvent type and operating strategies that can reduce the steam injection and GHG emission significantly, and without significantly compromising the oil production. Two hydrocarbon pure solvents, propane and butane were recommended in this project to cut the steam injection drastically and without having a significant negative impact on the oil production. Among the two solvents, butane may be preferred. However, to reduce the cost further and cut energy input, propane may be a better choice than butane. Propane is cheaper than butane and it requires less energy to vaporize propane. The process should start with steam-only injection (as SAGD) and next inject solvent after the chamber is somewhat developed. The solvent may not be effective if the oil production is already in the natural decline stage. At later stages, the solvent retention in the reservoir could also be high. During the solvent injection period, a small amount of steam could be continuously injected with the solvent or steam could be intermittently injected as needed to keep enough energy in the reservoir. This will help to vaporize the solvent and prevent the chamber from being cooled down significantly.