Research On The Damage Mechanism And Optimization Of Cavity Strings In Salt Cavern Storages

With the fast development of natural gas industry and the operation of projects like ‘West-to-East Gas Transmission' and ‘Sichuan-to-East Gas Transmission' in China,the adjusting function of underground gas storage becomes more and more important in the gas supply chain.Gas storage in salt caverns is one of the major forms of underground gas storage in China.During the dissolving process of salt caverns,tubular strings always encounter severe bending and collapsing,which not only greatly increases the construction cost but also requires longer construction time as a result of unavoidable workovers.This paper mainly focuses on the bending mechanism of cavity strings and the lab experiment of brine corrosion.Following works have been done:Based on the field investigation of gas storage in salt caverns,the parameters that resulted in the bending collapse of strings were analyzed.On the basis of the oscillation equation of single-flow pipe in vibration mechanics,the simplified model for tubular strings in caverning was built.Mesh and computation were accomplished by means of numerical simulation with fluid-structure interaction in ANSYS.It was revealed that under current working conditions,the bottom of the strings had the largest oscillation amplitude,which would lead to the vibration buckling of strings and consequently induce severe impact wreckage.The effect of axial stress on the strings was analyzed using theoretical method.In addition,the lab experiment program concerning the effect of brine corrosion on strings was designed and conducted.It turned out that higher temperature,brine concentration and flow rate would all accelerate the corrosion of strings.Compared with N80 strings,J55 strings which are currently used in caverning endured more corrosion.Through this study,the reasons for collapse of tubular strings during the dissolution of salt caverns are clarified.According to field conditions,corresponding solutions are given to prevent or alleviate strings collapse.Besides,this paper provides references for the material selection of tubular strings in dissolving salt caverns.