Abstract: During thousands of years of salt mining in China, a large number of brine-mining salt cavities have been formed. Compared with underground salt cavity gas storage reservoirs, brine-mining salt cavities are characterised by complex geological conditions, extremely irregular cavity morphology, and poor confinement and stability, etc. In order to study the sealing performance of brine-mining salt cavities, this paper with the thin irregular brine mining salt cavity as the research object based on the results of geological, logging and laboratory coretests, a three-dimensional fine geological model and a three-dimensional dynamic geomechanical model of the Y Salt Cavity and wellbore in the Sichuan Basin were established, and numerical simulations of the micro-annularity and fracture extension at the cementing interface were carried out. The results show that: 1) on the basis of clarifying the model permeability and pressure distribution, the simulation results show that the Y Salt Cavity in Sichuan Basin has good closure; 2) the fatigue damage and plastic strain under cyclic loading will be concentrated locally, mainly at the interface between the cement ring and the casing; 3) appropriately lowering the modulus of elasticity of the cement ring and the content of the fibre will enhance the closure ability at the wellbore; 4) when evaluating the closure ability of the salt cavity, the surrounding rock permeability is the main factor. During the construction of the salt cavity gas storage reservoir, a part of the thickness of the top plate of salt rock should be reasonably reserved according to the strength of the closure ability of the rocks in the region to guarantee the cavity tightness.

Key words: Sichuan Basin, brine-mining salt cavity, confinement, three-dimensional geological model, numerical simulation