Experimental research on capacity expansion simulation of multi-cycle injection-production in reconstruction of oil reservoir to underground gas storage

Abstract

Most simulation experiment methods of gas storage use the backpressure valve to control the fluid pressure and adopt the “huff and puff” mode, which is not quite consistent with the current model of “injection and production in different wells”. Backpressure valve control fluid pressure is challenging to control the injection-production rate, and the experimental repeatability is poor. Therefore, a new simulation experiment method of converting oil reservoir into gas storage is established based on controlling fluid pressure by capacitive liquid level meter and constant speed and constant pressure pump. It overcomes the defect of poor repeatability of conventional methods, facilitates oil-gas-water separation and monitoring, and conforms to the mode of “injection and production in different wells”. By this method, simulations of reconstructing gas storage from water-layer and reservoirs with different water saturation under high temperature and pressure were conducted. The expansion capacity in repeated injection and production are analyzed. The results show that the expansion capacity of the pure water layer is limited. Under the minimum operating pressure of 18 MPa, after 7 cycles of injection and production, the cumulative expansion capacity is 31.35 %. The higher the initial oil saturation of the gas storage remodeled from the reservoir, the stronger the expansion capacity. Reservoirs with water saturation of 39.28 %, 47.04 %, and 63.50 % were converted into gas storage. After 5 cycles; the oil retention rate decreased by 23.92 %, 21.72 %, and 17.97 %, the water retention rate decreased by 9.84 %, 10.79 %, and 13.88 %, and the cumulative expansion capacity is 33.76 %, 32.51 %, and 31.85 %, showing the dual effect of capacity expansion and enhanced oil recovery. This research deserves vital guiding significance for analyzing the expansion capacity during the repeated injection-production of the gas storage based on the oil reservoir and the selection of the construction time.