Feasibility and stability study of single-well retreating horizontal cavern gas storage in deep bedded salt rock of Liulin, China

In order to deal with the challenges of constructing underground salt caverns in Liulin salt district, which has a 1900m burial depth and layered structure, this paper has proposed and verified the efficacy of a novel, single-well retreating horizontal (SWRH) cavern construction method, which is advantageous to traditional methods in terms of cost efficiency, lower risk of leaking, and stability. In preparation for the analysis of the feasibility and stability of SWRH caverns, SWRH cavern shape was determined via physical similarity experiments and numerical simulation methods and the mechanical properties of surrounding rock were obtained using various tests, namely Brazil disk splitting, variable-angle shear, and triaxial creep, from the target formation. Thereafter, injection and withdrawal operations were simulated using a 3D-geomechanical model, which was generated based on the geologic structure and mechanical parameters of the target formation, at constant internal gas pressures (IGP) and cyclic IGP. The results of the simulations show that 26 MPa and 40 MPa are the lowest and highest constant IGP that satisfy the stability requirement and SWRH caverns also exhibit stability under cyclic IGP ranging from 26 to 40 MPa. Additionally, the displacement, plastic zone, and volume shrinkage of the cavern all decreased with increasing IGP and cycle frequency. Comprehensive analysis indicates that the SWRH cavern have high feasibility as gas storage in deep bedded salt formation.