Experimental Investigation of Injection Pressure Effect on the Natural Gas Storage in Aquifers

Abstract

Abstract-Storing natural gas in underground reservoirs is a key element in the gas supply market. Depleted oil and gas reservoirs, salt caverns and aquifers are major candidates for natural gas storage, and between them aquifers have a high potential for effective balancing of a variable demand market. Aquifers are underground water bearing formations which may extend over distances of several miles, and in the absence of depleted reservoirs, saline aquifers are a proper option for underground gas storage. Because of water and gas movements in the reservoir, it is worth to know about the flow behavior across the porous medium. The behavior of natural gas in contact with brine has not been considered widely in the literature, and the effect of injection pressure on the process has not been studied experimentally before. Therefore, for the first time in this research the natural gas storage capacity at different pressures were calculated and gas and water flow behavior under high injection pressures in a low permeability rock is investigated by experimental tests.Natural gas flooding experiments were performed using a core flood set up at constant temperature 46 °C, and in each test the low permeability core sample taken from an Iranian aquifer was cleaned by methanol injection for 24 hours. Then it was dried in oven at 90°C for 12 hours. After that the core was vacuumed for 8 hours and saturated by two pore volume of the synthetic brine with 210000 ppm salt concentration. After that natural gas was injected at a constant flow rate into the core plug saturated with brine, and at the gas breakthrough time experiments were stopped and the storage capacity of sample was measured by comparing its weight difference before and after the test. Obtained results illustrate that the injection pressure plays an important role in the gas storage process, and increasing the pressure improves the sweep efficiency and water withdrawal. In other words, by doubling the injection pressure from 80 to 160 bar the gas storage capacity enhances about 7%.Index Terms-Natural gas, storage, aquifer, pressure effect.

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“…The storage capacity is affected by the injection flow rate, pressure and salt precipitation. The storage volume increases with the increase in the injection pressure [741]. Further, the storage capacity is affected by the distribution of pore and throat in the reservoir and water lock [742].…”