Vapour extraction (VAPEX) process has a low production rate and is not suitable for thin reservoirs due to lack of efficient gravity drainage. Cyclic solvent process (CSP) has been proposed to improve the production rate of solvent processes. A major problem of CSP is that during production, the reservoir pressure has to be greatly reduced in order for the solvent gas drive to occur during which oil regains its high viscosity because a significant amount of solvent gas evolves out of oil. Also, at low-to-intermediate pressures, the methane solubility in the oil is not high. Additionally, continuous free gas saturation during early production results in high gas mobility and the pressure, and thus, the drive energy can be quickly depleted by gas production. To overcome the problems of VAPEX and CSP, a new process for in-situ heavy-oil recovery- Enhanced CSP (ECSP) is developed in this study. ECSP effectively utilizes the viscosity reduction and solvent gas drive mechanisms during the production.
ECSP experiments are performed to analyze the mechanisms and develop the optimal combination of two solvent slugs and injection/production strategy to optimize the injection process for improving the CSP in thin heavy-oil reservoirs. It is also shown that other ways of improving CSP is either to repressurize the system using water injection, i.e., conducting cyclic gas-alternating-water injection, or to conduct surfactant-enhanced CSP. Various aspects of ECSP are investigated under different injection sequences of two gas slugs. The impact of foamy solution gas drive mechanism on ECSP is also investigated. Then, phase behavior simulation is carried out for different heavy oil-solvent systems to predict the phase behavior of gas/gas mixtures with heavy-oil. Using a validated simulation model, the impacts of various parameters on ECSP are examined to analyze the mechanisms and illustrate the possible optimum ECSP designs.
This study has produced experimental results for CSP, ECSP, cyclic gas-alternating-water injection, surfactant-enhanced CSP, extended waterflood, PVT data and phase behavior simulation, detailed cyclic solvent injection technique, PVT and simulation models for evaluation and optimization of ECSP, history-match and parametric study of ECSP, and guideline of ECSP for thin heavy-oil reservoirs.