Risk Assessment And Control Method Of The Salt Rock Underground Gas Caverns

Energy strategic reserve of oil and gas is one of the most important means to ensure security and stability energy supply. It will be paid more and more attention by countries all over the world. The salt rock has the properties of low permeability, creep behavior, damage self-healing ability and other good characteristics. These properties has been used in salt rock underground gas storage to achieve the aims of safe, reliable, economic, saving land and protecting environment for energy strategic reserve. Some accidents happen frequently in foreign countries, such as destruction of gas storage, gas leakage and surface subsidence, etc. It has brought disastrous consequences to environment and energy reserve safety. Salt rock gas storage construction has just started in China. And the salt rock has the properties of shallower burial depth, lower thickness, multiple interlayer and lower grade compared with gas storage built in very thick salt rock in foreign countries. It will further increase project construction and operation risk. Therefore, study on risk assessment and regulation method of salt rock underground gas storage should be carried out in China to realize safe energy reserve of oil and gas.The research results of this paper lie in the following areas:(1) Risk holographic modeling of salt rock underground gas storage has been established and a method of responsibility scene filtration and qualitative severity classification filtration has been also proposed. Main risk sources during whole life cycle of gas storage have been displayed based on risk holographic modeling from seven aspects, project management, environment, technique, rock-mass mediums, gas storage entirety, controlling and function. By responsibility scene filtration and qualitative severity classification filtration, high and higher risk items should be mainly concerned by design, construction and operation organization have been determined.(2) First-order second-moment shown performance function used to analyze volume convergence failure probability of salt rock underground gas storage has been established and change law of volume convergence failure probability with internal pressure of gas storage and time could be obtained. Volume convergence failure probability decreases while internal pressure increases under the condition of long-term constant internal pressure of gas storage. And internal pressure value increases with time under the condition of same failure probability. Volume convergence failure probability increases while internal pressure decreases under the operation condition of low pressure gas recovery and the minimum internal pressure of gas storage should be kept above4.2MPa.(3) It could be obtained that volume convergence deformation of gas storage decreases while internal pressure increases and the minimum internal pressure should be kept above4.0MPa by model test. While volume convergence deformation showed a tendency of accelerated deformation under operation condition of high pressure and the maximum operation pressure should be less than22.0MPa. Changes of gas injection and gas recovery rate have a significant effect on volume convergence deformation. Gas injection rate should be controlled less than0.75MPa/d while gas recovery rate should be controlled less than0.65MPa/d.(4) Besad on the conclusion of Fuzzy comprehensive evaluation of the risk factors, Established the model of Risk assessment analytical hierarchy process of three accidents. Determined the weights distribution effected of different risk factors and obtained the level of three accidents.(5) Risk management program of salt rock underground gas storage has been established and risk regulation method, such as optimization of design scheme, dynamic control of construction and optimization of operation condition has been proposed. Optimization scheme of ellipsoidal cavity and key design parameters of layered salt rock gas storage has been determined. According to analysis results of three accidents failure probability, safe value range of pressure of operation condition, time, gas injection and gas recovery rate has also been determined.(6) System of project risk management and evaluation of salt rock underground gas storage has been established based on information technology and data stream, work flow, design of encapsulation and publishing of system have been completed. Six function modules, including project information database, risk management plan, risk identification and filtration, risk assessment, risk monitoring and risk emergency rescue, have been organically integrated to achieve the aims of storage, calling, analysis and processing of data. It will lay a foundation for improving project risk management level.