Experimental Study on Plugging of Micro-Leakage Interlayer (MLI) in Underground Salt Cavern Gas Storage (Jintan, China)

The permeability of a certain mudstone interlayer in underground salt cavern gas storage (Jintan, China) is slightly high, as indicated by pressure tests (leakage rate of approximately 1~2 L/d). This layer is referred to as the “Micro-Leakage Interlayer (MLI)”. The MLI significantly impacts the tightness of gas storage, potentially leading to substantial losses. To address this problem, an experimental study was conducted. Initially, a method utilizing brine crystallization to plug the micro-leakage interlayer (MLI) was proposed. After crystallization, the porosity of the MLI cores exhibited a notable increase, and the permeability of the MLI cores increased significantly, further exacerbating the risk of gas leakage. These results indicate that the plugging solution requires further exploration. Finally, a combined plugging solution utilizing brine crystallization and ultrafine cement was proposed. Using saturated brine and waterproof coatings, an ultrafine cement slurry was prepared, and specimens were created for testing. The results indicate that the specimens exhibited a porosity of approximately 3%, a permeability below 10−19 m2, and a uniaxial compressive strength of about 40 MPa. The ultrafine cement particles had an average particle size of 3 µm, and the ultrafine cement slurry exhibited extremely low porosity and permeability, as well as high strength. The results indicate that this solution is highly feasible and can be applied to field engineering.