Abstract:

Oil reservoir-based gas storage is a novel development model that has gained significant attention in recent years. Many oilbearing structures in China possess favorable conditions for conversion into gas storage, offering substantial potential for enhancing oil recovery, diversifying gas storage types, and meeting regional energy supply demands. In this study, full-diameter cores from the Banshen-37 Fault Block in the Dagang Oilfield were utilized to design multi-cycle alternating displacement experiments, tailored to the gas injectionproduction characteristics of reservoir-based gas storage. The experimental results showed that: ① Gas exhibited both displacement and extraction effects on water and oil, playing a positive role in increasing gas storage capacity. ② In multi-cycle gas-driven oil and water displacement alternating experiments, the expansion capacity increased with the number of injection-production cycles, following a power function relationship. The final expansion rates were 27.73% and 33.74%, respectively. Appropriately lowering the minimum operating pressure in gas storage could further enhance its expansion efficiency. ③ In multi-cycle gas-driven oil and water displacement alternating experiments,（with initial water saturation values of 47.04% and 63.50% for the core sample in the two experiments）, it was clarified that under oil-water coexistence conditions, the higher the water saturation, the weaker the expansion capacity of the gas storage reservoir, with the final expansion rates of 32.51% and 31.85%, respectively, for the two experiments. ④ Based on oil-gas relative permeability curves, a rapid method for predicting the productivity of single wells in converted gas storage was proposed, differing from conventional numerical simulation methods. Productivity equations and absolute open flow rates were established for various injection-production cycles. The findings provide valuable guidance for the early-stage capacity evaluation and productivity design of gas storage converted from oil reservoirs.

Key words: sandstone oil reservoir, converted gas storage, productivity prediction, gas production rate, laboratory experiment