Experimental and Numerical Investigation on Deep High-Pressure Vertical-Horizontal Well Channel-Steam-Assisted Gravity Drainage in Heavy Oil Reservoirs

Summary

Vertical-horizontal well steam-assisted gravity drainage (VH-SAGD) is a highly effective thermal recovery technology for heavy oil reservoirs. However, under deep, high-pressure conditions in heavy oil reservoirs, steam override and caprock heat loss reduce steam quality and thermal efficiency. The development mechanisms under these conditions remain unclear. In addition, conventional startup processes hinder the optimization of efficiency and cost. Ultimately, these factors restrict the development process. To address these challenges, vertical-horizontal well channel-steam-assisted gravity drainage (VH-CSAGD) technology is proposed. A 3D high-temperature and high-pressure physical simulation experiment was designed and conducted based on field sampling from the S Block in the Liaohe Oil Field, China. Through this approach, the steam injection process of VH-CSAGD was elucidated, along with the mechanisms of channel-assisted improvement. Expanded numerical simulations were also conducted to validate the laboratory experiments and field applications. Subsequently, a comprehensive evaluation system for development performance and energy efficiency was constructed. A sensitivity analysis was performed based on this system. The results demonstrate that a stable heat and mass transfer drainage channel was successfully formed at the reservoir bottom in VH-CSAGD. During the subsequent steam injection, a trapezoidal composite displacement pattern was generated, integrating hot water drive, steam drive, and gravity drainage. Steam override was effectively suppressed. The ultimate oil recovery factor reached 72.7% in the physical experiment. According to the numerical simulations, the preheating period was shortened, and the production build-up phase was advanced. Compared with conventional VH-SAGD, this technology significantly enhances the development performance and energy efficiency. A bottom channel strategy and a stepwise-increasing steam quality injection method were proposed. Furthermore, an optimal well spacing of 20.0–50.0 m was determined, and a reservoir thickness exceeding 20.0 m was required. These findings provide theoretical and technical support for efficient VH-CSAGD development under deep, high-pressure conditions in heavy oil reservoirs.