Utilization of carbon dioxide and methane in huff-and-puff injection scheme to improve heavy oil recovery

Previous studies showed that using non-condensable gases in huff-and-puff is successful in producing light oil components, but heavier components cannot be produced during the puff cycle. This study aims to validate the feasibility of solvent based huff-and-puff method with respect to enhancing heavy oil recovery for a wide range of operating conditions. Thus, an experimental approach was applied and a physical model with 1.774 μm2 absolute permeability and 24% porosity Berea core mounted in a high pressure stainless steel core holder was designed. For all tests, the core was saturated with a sample of Saskatchewan heavy oil with viscosity of 952 mPa s at 28 °C. Over eight sets of huff-and-puff experiments at different operating pressures and a constant temperature of 28 °C were performed, utilizing the pure carbon dioxide (CO2) and pure methane. A soaking time period of 24 h and a cut-off pressure of 276 kPa were considered for all cycles. In addition, each set of cyclic injection process were continued until production dropped below 1% of the original oil in place. Hence, 66 huff-and-puff cycles were performed. Considering the performance of all tests, at higher operating pressure the produced oil was lighter and the recovery factors were higher due to higher diffusion coefficient and solubility factor of solvent. Ultimate oil recovery of 71% was obtained by injecting pure CO2 at near supercritical condition of 7239 kPa and 28 °C, while that of pure methane at the highest operating pressures of 6895 kPa was 50%. The governing mechanisms contributed to the production were recognized to be solution gas drive, viscosity reduction, extraction of lighter components, formation of foamy oil and to a lesser degree diffusion process. The produced oil viscosity was reduced to 62 mPa s (at 28 °C) by injecting CO2 at 7239 kPa. In addition, most of the produced oil occurred during the first five cycles for each set of huff-and-puff test. The highest incremental recovery for all CO2 tests occurred at the 2nd, while that of methane happened at the 3rd cycle. Also, the solvent diffusion process was identified qualitatively by pressure depletion around the core during each experiment.