Investigating the heated zone evolution and production performance of cyclic steam stimulation with horizontal well in thick-layer heavy oil reservoirs

Abstract

Cyclic steam stimulation with horizontal well (CSSHW) has emerged as an efficient commercial recovery technique for heavy oil reservoirs. Accurately calculating the evolution of the heated zone and the production performance closely linked to it is crucial for addressing the economic and environmental issues that arise in the CSSHW process. Most previous analytical or semi-analytical models have relied on the assumption of uniform temperature distribution and have focused on thin-layer heavy oil reservoirs. In this study, through analyzing the evolution of the heated zone in the CSSHW experiment, the study observes that the temperature distribution within the heated region is non-uniform and exhibits a centrally symmetric distribution with the wellbore as the axis. Then, a semi-analytical model was developed to predict the heated zone evolution and production performance of CSSHW for thick-layer heavy oil reservoirs. Next, the model was validated using field data and numerical simulation. Finally, this study analyzed the evolution of the heated zone under a multi-cycle mode and examined the effects of various factors on oil production. The results reveal that the heat, the area, and the average temperature within the heated zone all increase with the number of cycles attributed to the influence of residual heat. Single-variable analysis indicates that increasing BHP reduces the pressure differential, lowering oil production, and that permeability significantly affects oil production. Multivariate analysis shows that lowering BHP with constant steam amount improves COSR or thermal efficiency. Lower steam amount achieves higher efficiency in high vertical or horizontal permeability reservoirs, while higher BHP maintains high efficiency in such reservoirs due to better fluid mobility. The temperature-dependent threshold pressure gradient (TTPG) analysis reveals that although TTPG reduces oil production, the reduction lessens with more cycles. TTPG's impact varies with steam amount, BHP, and permeability; increasing steam enhances TTPG's effect in low vertical or horizontal permeability reservoirs, while higher vertical or horizontal permeability reduces TTPG's effectiveness. This article provides a tool for rapid optimization and performance forecasting in thick-layer heavy oil field applications.