Abstract: The salt cavern underground gas storages in China are mostly built in layered salt rock strata with varying permeability. Ensuring good airtightness of the salt cavern gas storages is important. To solve the problem that the “open-hole section” of the wellbore accidentally traverses the micro-permeable layer and causes the airtightness failure of gas storage, a grouting test platform for plugging the micro-permeable layer was independently developed and a feasibility test of grouting plugging was designed based on the geological leakage situation on site. After determining the proportion of slurry with fluidity and filling compactness, an experimental study on plugging cores with ultra-fine cement was conducted. The test results show that the ultra-fine cement can effectively fill the pore and reduce the core permeability. The porosity and permeability of the cores are decreased by about 16% and 95% after the grouting tests. The plugging test data show that the plugging range is in the power function relationship with the grouting time, and the grout flow pattern satisfies the power law flow instead of the Newtonian flow. This study can provide theoretical and experimental basis for the grouting method to plug the micro-permeable layer in salt cavern gas storage, and it is critical for the secondary utilization of similar airtightness failure of the wellbore.

Key words: salt cavern underground gas storage, micro-permeable interlayer, ultra-fine cement, grouting, seepage migration