Study on the long-term airtightness of salt cavern gas storage considering the permeability variation of surrounding rock

To analyze the variation laws of seepage range and pore pressure within surrounding rock during the long-term operation of salt cavern gas storage, a basic differential equation for seepage considering the variation in porosity and permeability of surrounding rock with time was established based on the constitutive equation of porous media. The seepage differential equation was solved using the plane radial seepage theory and the spherical centripetal seepage theory. Then the prediction model for the horizontal and vertical seepage range of salt cavern gas storage was constructed, and the relationships of seepage range with operating time and pore pressure with seepage distance were derived. On this basis, the variation laws of the seepage range and pore pressure within the surrounding rock of a proposed salt cavern gas storage were analyzed using the theoretical model, and the pillar width, roof thickness and floor thickness of the storage were determined from the perspective of long-term airtightness. Moreover, the rationality of the theoretical model was verified utilizing the numerical simulation method. The results indicate that the calculation results obtained by theoretical model are in good agreement with the numerical simulation results. Finally, the influences of the initial permeability of salt rock and the interlayer location on the airtightness of the salt cavern gas storage were studied using the theoretical model.