Experimental investigation on cyclic steam stimulation assisted modified THAI to enhance oil recovery in steam-treated heavy oil

Steam injection is well accepted as a main method for heavy oil reservoirs. Currently, most heavy oil reservoirs have reached the late stage of steam treatment and encountered various challenges thus alternative methods are needed to develop the remaining oil. CSS1 Assisted Modified THAI2 (CSSAMT) is proposed to be an effective follow-up method in heavy oil reservoirs treated by steam. CSSAMT combines the benefits of ISC3 and steam, with steam acting as a protective agent for production wells threatened by combustion as well as a restrainer for oxygen breakthrough. A 3-dimensional physical model was conducted for the experiment to simulate the process and investigate the mechanism. The result demonstrates the feasibility of the CSSAMT process with a high oxygen availability of 99.8% and an average apparent H/C ratio of 0.71, achieving an oil recovery factor of 44.01%. Optimal steam injection parameters were determined as a 0.03 T (dimensionless time)-soak period followed by a 0.06 T production period. Additionally, oil upgrading results were quantitatively described through the carbon number variations, and a prediction formula correlating the sweep efficiency and the carbon number variations was proposed, showing a correlation coefficient of 0.9. •CSSAMT as a new EOR method is proposed.•Mechanisms and oil upgrading performance of CSSAMT are revealed.•Other processes (liquid production, oil upgrading characteristics) are quantitatively analyzed.•An empirical formula was established to predict the sweep efficiency.