Research on Influencing Factors in the Development Mechanisms of Steam Chambers for Offshore Thick-Bedded Extra-Heavy Oil in SAGD Production

SAGD is an effective way to enhance super-heavy oil recovery after cyclic steam stimulation CSS procession. The good formation and expansion of steam chamber is the key to successful implementation of SAGD. In development of thick extra-heavy oil, the development characteristics of steam chamber can be monitored by observing wells on land. However, for offshore large well spacing mode, it is difficult to judge the production state and make adjustments due to the lack of monitoring means. Therefore, it is necessary to study the expansion characteristic and influencing factors of the steam chamber.To address this issue, reservoir numerical simulation was employed to integrate steam chamber evolution patterns with 3D experimental production curves. By establishing their correlations, a SAGD development stage chart was developed, which clearly defines three development phases with corresponding steam chamber configurations and production characteristics. According to the chart, history matching of 3D physical model experiments was conducted through numerical inversion using the STARS module of CMG simulation software, establishing a same-scale numerical model for extended studies. Through expanded numerical simulation, comparative analysis was performed on key geological factors influencing steam chamber development, including reservoir thickness, heterogeneity, and aquifer multiples. The results show that oil layer thickness mainly affects the time of the rising and horizontal expansion of the steam chamber. The heterogeneity mainly affects the rising and downward expansion speed. The water volume mainly affects steam chamber size. Top water drastically reduces ultimate recovery and prematurely terminates stable production and also intrusion causes severe steam chamber degradation. Interbedded layers impede the vertical development of the steam chamber, effectively reducing the reservoir's productive thickness and degrading recovery efficiency. The research results support the completion of offshore SAGD production planning, which has important guiding significance for improving the development effect of thick extra-heavy oil reservoirs, especially the optimization of production system after cyclic steam stimulation.