An innovative method to deal with thick insoluble interlayers in the solution mining of salt-cavern gas storage

At present, the most popular method to deal with thick insoluble interlayers in the solution mining of salt-cavern gas storage is to weaken the strength of the insoluble interlayers by immersing them sufficiently until they collapse naturally.For thick insoluble interlayers whose thickness is more than 10 m, however, the collapse is quite difficult. The critical collapse span for the thick insoluble interlayers could be as much as 60 m, and its collapse by full immersion takes long time, so that the solution mining efficiency is decreased and the leaching strings below thick interlayers may be damaged. In this paper, an innovative solution mining method in consideration of thick interlayers was proposed with the geological data of one well in Huai'an Gas Storage as an example. In this innovative method, solution mining is carried out separately above and under the interlayer. A conventional vertical cavern is leached above the interlayer, while a horizontal cavern is leached below the interlayer. The cavern above the interlayer is horizontally staggered from the one below the interlayer to maintain the stability of the thick insoluble interlayer as the roof of the horizontal cavern. It is indicated from the simulation results that by virtue of this innovative method, a cavern volume of 50 000 m³ more can be created in the same conditions of salt layer, and the damage risk to the leaching string below the interlayer can be avoided. Finally, it was recommended to arrange wells by the cluster well technology so as to reduce land charges and rig moving and installation expenses while optimizing the drilling procedure by adopting the mobile drilling unit so as to improve the economical efficiency of drilling operation in the process of solution mining.