Shaohao Huang, Zhibin Li, Xuefeng Song, Binshan Ju, Chen Zhang, Bing Xu
Heavy oil reservoirs often retain substantial remaining oil after polymer flooding with vertical wells due to unfavorable oil-water mobility ratios and reservoir heterogeneity. Although horizontal wells can improve oil displacement efficiency by providing a larger contact area with the formation, systematic studies on the displacement behavior and key influencing factors of polymer flooding in opposed horizontal wells are still lacking. This study addresses this gap by combining two-dimensional physical simulation experiments with Eclipse numerical simulation to investigate the displacement dynamics and remaining oil distribution. The experimental results show that increasing well spacing prolongs the water-free oil production period and enhances final recovery. At the same time, the recovery at a crude oil viscosity of 50 mPa$\cdot$s is 15.31% higher than that at a crude oil viscosity of 300 mPa$\cdot$s at a well spacing of 14 cm, indicating that horizontal well polymer flooding is more effective in relatively low viscosity heavy oil reservoirs. Numerical simulation shows that the optimal distance is 390 m, beyond which the incremental recovery will become negligible. Both experimental and numerical simulation results confirm that polymer flooding in opposed horizontal wells can effectively alleviate water fingering and channeling, delay water breakthrough, and improve sweep efficiency. In the vertical direction, the remaining oil saturation of the middle layer increases from the inside out, with higher saturation in the upper part than in the lower part, and better recovery rates are observed at lower reservoir positions. By providing experimental validation, this study not only serves as a basis and verification for numerical simulations, but also offers scientific insight and engineering guidance for optimizing polymer flooding strategies in unconventional and mature horizontal-well reservoirs.