Corrosion Risk Analysis And Safety Design Of Injection-production String In Underground Gas Storage

In recent years,with the rapid development of natural gas pipe network and natural gas industry,the development of underground gas storage facilities has been promoted rapidly.However,in the early stage of operation,there exist residual drilling fluid,hydrochloric acid,condensate water,carbon dioxide,hydrogen sulfide and other acidic gases,which make the underground environment very complicated.The injection-production string will always be in the corrosive environment.Therefore,it is of great significance to analyze the corrosion risk of underground gas storage string and make relevant anti-corrosion measurements.In view of the factors affecting the corrosion risk of the string in underground gas storage,this paper has carried out the following aspects based on the foundation of previous researches:(1)The operating conditions and common failure modes of the string in underground gas storage is introduced,and the main corrosion types and influencing factors of the string are summed up.The main factors affecting the corrosion rate and the interaction mechanism between various factors are obtained based on the previous experimental result data of corrosion mechanism.According to the domestic and foreign standards,the strength calculation theory of each corrosion model is analyzed,and the failure criterion for the injection-production string with corrosion defects is determined.(2)The finite element model of corrosion defect of the injection-production string is established by ANSYS software.The influence rule of uniform corrosion and pitting corrosion model on stress intensity of the injection-production string is analyzed.The influence rule of corrosion defect depth and length on the stress intensity of the string is obtained by analyzing the uniform corrosion model;The influence rule of the pitting section and pitting depth on the stress intensity of the string is obtained by analyzing the pitting corrosion model.(3)Combined with the corrosion failure statistics data and corrosion influence factors of injection-production string of underground gas storage,a fault tree model based on corrosion failure of injection-production string is established.Through qualitative and quantitative analysis,the minimum cut set and the probability of top event occurrence of fault tree is obtained.The importance ranking of all basic events that result in the top event is obtained by fuzzy importance analysis.By combining the fault tree model with Bayes network,we can get the risk level of the top event of the fault tree is 1×10-2.The result can make a comparison validation with the result of fuzzy fault tree method,and 3 critical failure causation chains are figured out based on probability updating analysis.Finally,some specific anti-corrosion measures are suggested.(4)By using Visual Studio 2013 platform create a set of safety design software which is applicable to the injection-production string of underground gas storage,which can improve stress analyse calculation efficiency effectively at the string work time.Also we can more intuitive understanding the stress state and safety factor when the string is under the work condition.The software is applied to verify the feasibility of the design of an underground gas storage string,and provide the basis for the design of the injection-production string.