The flue gas-solvent assisted steam assisted gravity drainage studies: experiments and numerical simulation in extra-heavy oil reservoirs

Steam-assisted gravity drainage (SAGD) has been used successfully for developing extra-heavy oil around the world. But many experiments and field production have pointed out problems, such as heat loss to the overburden and low oil-steam ratio. Compared with SAGD, flue gas-solvent assisted SAGD (FGS-SAGD) is a relatively new thermal recovery technology. FGS-SAGD combines the multiple advantages of gas injection, solvent injection, and thermal recovery processes. In this paper, 3D sand pack models were established to study the steam chamber expansion characteristics and the development performance of different drainage experiments. Numerical models based on the experimental parameters were conducted to further study the gas and solvent migration and its effect on the temperature and oil saturation profiles. The results show that in the process of FGS-SAGD, the accumulation of flue gas effectively inhibited steam override and reduced heat loss to the overburden, which slowed the vertical expansion of steam chamber and improved the lateral expansion of steam chamber. Solvent was vaporized under high temperature and mixed with extra-heavy oil at the edge of steam chamber to reduce oil viscosity, which further improved the profile of steam chamber. Both flue gas and solvent injection significantly improved the heat utilization efficiency and increased the steam sweep volume and oil recovery. The oil recovery of FGS-SAGD (41.9%) was 12% higher than that of SAGD in the experiments. In addition, the oil mobility was increased by 26.2%, and water phase mobility was decreased by 19.7% in the process of FGS-SAGD. The study indicates that FGS-SAGD is a feasible technique for improving development performance in extra-heavy oil reservoirs.