Repair of irregularly shaped salt cavern gas storage by re-leaching under gas blanket

Abstract

During cavern leaching for salt cavern gas storage in China, cavern shape irregularity has become a growing problem. It reduces cavern volume and the utilization ratio of the salt formations. The collapse of the irregular parts may cause downhole accidents and threaten cavern stability. In this paper, shape repair of an irregular salt cavern by re-leaching under gas blanket is proposed for the first time in China. The technological process of the cavern repair under gas blanket is introduced. A mathematical model is set up to predict the real-time three-dimensional shape of the salt cavern during the repair process. The upper and lower limit of the gas-brine interface, the depth of the leaching tubing and the salt-brine mass transfer rates are included in the model. The coupled equations for shape prediction are derived, which consider the effects of brine concentration and velocity. A VC++ program is developed based on these equations. To verify the proposed model, the repair process of a gourd-shaped salt cavern is carried out in the laboratory and is simulated by the program. The comparison of the experimental and simulation results shows that the proposed model has a high accuracy. The prediction model and the VC++ program are used in the field repair work of JT86 cavern of Jintan underground gas storage. The irregular parts are well repaired, and the cavern is enlarged by about 9000 m3. The sonar imaging and injection-production data of the repaired cavern coincide well with the simulation results obtained by the proposed model, which further validates the reliability and precision of the model.