Cold CO₂ and steam injection for heavy oil recovery

Steam-Assisted Gravity-Drainage (SAGD) is one of the most effective ways of recovering heavy oil. Injection of cold solvent into the SAGD formation is an enhancement to SAGD recovery technology to reduce the energy consumption and heat loss. SAGD process is a high energy-intensive process where it requires a high amount of steam to mobilize and recover the heavy oil. Besides, generation of steam requires the combustion of natural gas which adversely impacts the economics of SAGD, especially when the price for natural gas is high. Furthermore, large amounts of injected steam are retained in the reservoir where it reduces the thermal efficiency of the process. Therefore, this research aims to develop better recovery process with lower energy and emission intensities. In this study, a thermal compositional simulation was carried out using a commercial simulator to examine the performance of cold solvent in assisting heavy oil recovery. In this process, the cold solvent is injected into a mature heavy oil field where it has been recovering using SAGD process. The solvent will then utilize the energy retained in the reservoir to vaporize and spread within the steam chamber. The low temperature of the solvent will cool down the temperature of steam chamber where it enhances the solubility of solvent in the oleic phase and accelerates recovery. Carbon dioxide is chosen as the solvent for this process as it is considered as a lower-cost alternative compared to hydrocarbons. The simulation shows a secondary peak oil rate due to the cold solvent, followed by a steady increase in oil production rate. This is also aided by the viscosity reduction due to carbon dioxide solubility. Steam injection is ceased when a cold solvent is injected into the formation, hence significantly reducing the steam requirement in heavy oil recovery. Overall results show that the cold solvent process increases the oil recovery by 2%, reduces steam-oil-ratio, reduces total heat loss by 16% and reduces steam requirement by 24%. Hence, the advantageous results from the simulation prove that cold solvent is a profitable and energy-efficient recovery method in recovering mature SAGD formations.