Study on the Influence of Secondary Water Body in the Near-Well Region on the Oil Bank Formation and Movement

In-situ combustion (ISC) is an effective follow-up technique for the heavy oil reservoirs developed by steam injection. However, the influence of secondary water body (SWB) generated during cyclic steam stimulation on the formation and movement of the oil bank remains unclear and requires further investigation. Oil sand with varying water saturation was packed near the injection end of the combustion tube to simulate SWB formed during cyclic steam stimulation development. This study investigated the effect of the water content in SWB within the near-wellbore region on oil bank formation, movement behaviors, and oil recovery performance. The results show that appropriate SWB saturation near the wellbore promotes the formation of thicker, mobile oil banks and enhances oil recovery, while excessive water hinders oil bank development and disrupts stable combustion. When the SWB water saturation is below 27.9%, the evaporated water enhances oil mobility, promoting the gradual accumulation and stable migration of a thick oil bank with a maximum thickness of 18.2 cm and an oil saturation of less than 68%. This condition facilitates sustained fire front propagation, efficient oil displacement at relatively low pressure, and a high oil recovery factor. In contrast, when the SWB water saturation exceeds 41.9%, premature air breakthrough occurs, disrupting the continuous accumulation of the oil bank, which results in a reduced oil bank thickness ranging from 10.6 cm to 12.2 cm and leads to unstable fire front advancement. Nevertheless, the enhanced oil displacement effect from evaporated water under high saturation conditions can still yield an oil recovery factor exceeding 61%. These findings enhance the understanding of the impact of SWB near air injection well on oil bank formation and movement, which provides theoretical guidance for the application of ISC technology in steam flooded reservoirs.