Abstract: Underground gas storage (UGS) facilities in China are predominantly developed in gas reservoirs, exhibiting limited diversity, while UGS conversion from depleted oil reservoirs remains in its nascent stage. To address key challenges such as complex post-waterflood fluid distribution, intricate seepage mechanisms, and undefined technical policies for synergistic development, this study focuses on the X Oil Reservoir in the Jidong Oilfield. A comprehensive investigation was conducted to optimize collaborative hydrocarbon recovery enhancement and storage capacity expansion. By integrating high-resolution geological characterization, dynamic evaluation of individual well injectivity/productivity, and optimal well pattern selection, a numerical simulation model was established. Quantitative analyses were performed to evaluate the impacts of full-cycle liquid drainage, timing of transitioning to areal flooding, and staged pressure ramp-up on storage capacity utilization and oil recovery. The results are as follows: 1) Full-cycle liquid drainage significantly enhances drainage rates and working gas volume compared to conventional methods; 2) The optimal transition to areal flooding occurs when the gas front reaches the structural low, effectively mitigating gas breakthrough risks while accelerating working gas formation; 3) A“staged and stepwise pressure ramp-up” strategy is proposed, with the initial pressure increase timed at the shift from single-pattern gas drive to areal flooding, enabling synchronous growth in both storage capacity and drained liquids. Simulation forecasts indicate that the“full-cycle drainage + pressure ramp-up” mode will achieve the target working gas volume of 10.52×10⁸ m³ by 2034—2035, maximizing both storage space and recovery efficiency. These results provide critical technical foundations for realizing the“high deliverability with fewer wells and efficient UGS development” objective in similar depleted oil reservoir conversions.

Key words: collaborative construction of reservoir-type UGS, EOR and capacity expansion, well pattern optimization, injection-production scheme optimization, numerical simulation