Experimental and numerical study of steam-chamber evolution during solvent-enhanced steam flooding in thin heavy-oil reservoirs

Abstract

Steam flooding (SF) is an effective technology to exploit thin heavy-oil reservoirs. Long-term indoor experiments and field tests, however, show that SF has the problems of great heat loss and a limited steam-chamber affected area, which severely limits steam utility and the ultimate economic benefit of thin heavy-oil reservoirs. In this paper, based on a specific oil field in China, we designed a two-dimensional experimental model to investigate the effect of solvents on steam-chamber distribution and production dynamics, and the effect of heat-solvent coupling (molar ratio of steam and solvent) on steam-chamber front expansion. Then, based on the parameters of indoor experiments, we built a numerical model by CMG STARS to further study the influence of solvent migration in steam chambers under different injection molar ratios of steam and solvent. The results show that: i) According to experimental results, for SF, steam-chamber affected area is limited and oil recovery is low which is only 21.3%. After the solvent is added, steam-chamber affected area can be largely enlarged and displacement efficiency can be enhanced. Compared with SF, oil recovery of Solvent-Enhanced Steam Flooding (SESF) can be enhanced to 34.3%–58.3%; ii) According to the results of the numerical simulation, oil viscosity can be greatly reduced after the solvent is added. As a result, steam-chamber expansion can be improved, steam-chamber affected area can be enlarged, and displacement efficiency can be enhanced; iii) the optimal injection molar ratio of steam and solvent was around 8:1 for SESF.