Research on Injection-Production Capability and Seepage Characteristics of Multi-Cycle Operation of Underground Gas Storage in Gas Field—Case Study of the Wen 23 Gas Storage

Abstract

With the increasing energy demands of current modern society, underground gas storage (UGS) in gas fields is the most popular type of UGS used to meet the seasonal variation of gas consumption. However, compared with gas fields, UGS in gas fields has the characteristics of periodic high-speed injection and production of exploitation modes and operation rules, which causes the rules of gas-water seepage and utilization of reserves to be more particular and complicated. In this paper, based on Wen 23 gas storage, the rules of multicycle injection and production flow and the utilization of UGS pore volume were investigated. The experimental results showed that variation in porosity and permeability caused by injection and production pressure changes in Wen 23 gas storage can be neglected. The pore volume of gas storage and the degree of gas recovery increased gradually in the pre-UGS gas zone, which was higher than that of reservoirs. In the initial stage of UGS operation, the pore volume of gas storage and the degree of gas recovery were low in the gas-drive-water gas zone as a result of water invasion during the process of reservoir exploitation. During operation of multicycle high-speed injection and production, the seepage conditions in the gas-drive-water gas zone gradually improved. The higher the reservoir permeability, the greater increases in pore volume and degree of gas recovery. In the gas-water transition zone, gas and water were reciprocated and displaced with the multicycle injection-production of UGS, resulting in the gradual deterioration of pore volume and gas recovery, which remained stable at a low value. The negative effects of reservoir heterogeneity on the effective utilization of UGS occurred in the gas-water transition zone. These findings may contribute to a better understanding of the rules of multicycle injection and production flow and utilization of UGS to optimize the injection-production efficiency of Wen 23 gas storage.

Research status of CO2 as cushion gas in underground natural gas storage

“…During the multi-round injectionproduction process in the gas storage, some pores that were originally occupied by water and crude oil are filled with injected gas, and frequent injection and production causes changes in reservoir temperature, pressure, geological structure and so on, resulting in changes in injection and production capacity and storage capacity [56][57][58] . Researchers obtained the following conclusions through multiple rounds of "gas-water" interdrive experiments: 1) Wettability had a significant effect on the characteristics of gas-water co-driving and infiltrating flow; 2) Multi-cycle gas-water co-driving could cause an increase in the relative permeability of the gas phase, a decrease in the relative permeability of the water phase, and an increase in the residual gas saturation in the coexisting zone of gas and water; 3) The reciprocating movement of water during the operation of the gas storage caused the formation of a large number of dead zones in the pore space of the reservoir, resulting in a decrease in the availability of the pore space and storage capacity utilization; 4) For reservoirs with widely developed fractures, multi-cycle gas-water co-driving produced certain water blockage damage, reducing the effectiveness of storage capacity utilization [59][60][61][62][63][64][65] . However, the above conclusions may not necessarily apply to the gas storage of CO2 as cushion gas.…”

Physical Simulation Experimental Technology and Mechanism of Water Invasion in Fractured-Porous Gas Reservoir: A Review

“…China's annual natural gas output has exceeded 100 million tons of oil equivalent, and natural gas consumption has grown at an average annual rate of 12% in the past decade, playing a significant role in the country's transition to low-carbon energy [1][2][3][4][5][6][7][8][9][10]. Proven reserves of aqueous gas reservoirs account for more than 50% of conventional natural gas in China, which is the core area of natural gas development to increase production [11].…”