Solution mining technology of enlarging space for thick-sandwich salt cavern storage

Aiming at the current problem that thick sandwiches are commonly developed in domestic salt mines, this study investigated whether thick sandwiches would collapse to allow connection of salt deposits above and below, consequently expand single cavern capacity by laboratory experiments, numerical simulation and field tests. The analysis of water-soluble mechanism and changing patterns of mechanical parameters of sandwich layers after water immersion shows that: after water immersion, sandwiches dissolve into honeycomb structure with cracks that easily flake, and the residues occupy small space; after water immersion, mechanical strength of sandwiches decrease greatly, susceptible for failure and collapse. Based on the calculation model for critical limited span, the collapse timing was predicted. In addition, laws of thick sandwiches' collapse were obtained by numerical simulation, which indicate that the smaller thickness, as well as the larger depth, limited span and storage height of the sandwiches are more likely to cause the sandwich collapse. The design idea of “full immersion and secondary cavity construction” was proposed, and cavern leaching design for a 12 meter thick sandwich in a gas storage was made, and tests on two wells were conducted. The results prove that thick sandwiches could collapse, increasing leaching height and single cavity capacity, and the technology is technologically and economically feasible.