Objective Underground gas storage involves significant equipment and facilities for compression, filtration, and metering. Methane escape or leakage may occur at the sealing points of valves, connectors, open pipes, flanges, and other equipment, leading to environmental pollution and operational risks. However, a method for quantifying methane escape from these sealing points and an inversion equation for the escape rate are not yet available both domestically and internationally.

Methods This study took an underground gas storage as the example, with field measurements conducted at sealing points of 2,030 sets of equipment in six areas, including the separation, metering, well site, and inlet and outlet areas. The analysis examined the distribution intervals of methane escape volume fractions and the leakage probabilities for four types of equipment in these six areas. Based on the measurement results, the inversion equation for converting methane escape volume fraction into escape rate was revised to quantify the methane escape from the sealing points of surface equipment for the underground gas storage.

Results Seventy leakage points with methane escape volume fractions exceeding 0.01％ were identified in the gas storage, primarily located in the inlet and outlet valve group area, gas skid area, and filtering & separation area. The proportions of leakage points at connectors, flanges, valves, and open pipes were 40％, 26％, 20％, and 14％, respectively. The calculated methane escape from the equipment sealing points of the gas storage was approximately 2.4 t/a, with 0.44％ of these points contributing to about 90％ of the escape. The revised inversion equation was compared with those from the Environmental Protection Agency (EPA) and Lan Facong, showing similar calculation results for small-diameter connectors and open pipes, while yielding higher results for large-diameter valves and flanges.

Conclusion The calculation result of the revised inversion equation represents the total amount of escape from the equipment, providing a more accurate estimate of methane escape. In addition, the localization of inversion equation has been achieved, offering a basis for quantifying the total methane escape from equipment sealing points of underground gas storage in China and informing strategies to reduce methane emissions from surface equipment.