Use of Acid Gas (CO2/H2S) for the Cyclic Solvent Injection (CSI) Process for Heavy Oil Reservoirs

Abstract

ABSTRACT Acid gas is a greenhouse gas (GHG) composed of (CO2/H2S). It is produced during oil, gas, and petrochemical operations. During the last several years, there has been an increasing pressure within the oil industry in Canada to further reduce GHG emissions. Another environmental problem within the oil industry comes from the elemental sulphur, which is converted from the H2S and is accumulated on the surface. Currently, there exist two technological solutions to deal with this challenge. The first one is acid gas injection into geological formations for sequestration purposes. This option has been developed in Canada over the last 22 years. The second one is the use of it for EOR operations in conventional oil reservoirs. This option has successfully been applied in Zama, a Canadian conventional oil reservoir. There is an interest within the oil industry again to evaluate the performance of CO2/H2S to also recover heavy oil during the Cyclic Solvent Injection (CSI) process. The CSI process has already shown success in improving heavy oil recovery after primary cold production (CHOPS) using pure solvents or (CO2 /propane or CH4/propane) mixtures. Consequently, if feasible, CO2/H2S injection for CSI could also contribute to increase the heavy oil recovery factor while eliminating the accumulation of sulphur on the surface and sequestering this greenhouse gas. The results of this work indeed demonstrated that the CO2/H2S mixture tested performs better for the CSI process than some of the conventional solvents previously tested i.e. pure CO2 or methane/propane mixture. Not only the recovery factor was better but also the oil recovery declined less with subsequent cycles by using CO2/H2S mixture rather than using pure CO2. It is important to mention though that the mixture of CO2/propane still shows the best performance in the series of solvents studied so far for the Cyclic Solvent Injection at Alberta Innovates Technology Futures.