| The salt rock has the excellent properities of creep behavior, low permeability, damage self-healing ability and other good characteristics, such as high area utilization,big instantaneous throughtput, easy excavation and so on. It has become a common understanding worldwide that salt rock makes good natural gas storage. Although compared to other underground energy reserves salt rock has better security, salt rock in china has it own characteristics, such as thin salt layers, many non-salt interlayers, low salt degree, etc. By referring to the foreign salt rock gas storage accidents, accidents accounted for 19% in the construction period.The construction of gas storage caverns in salt rock is a complicated system engineering. There are many complex problems in the building process with water solution. For example, what process combination to choose to come into being the design shape and the process combination includes many aspects, referring to the cycle of water solube, fresh water injection rate, colum combination, roof and floor proction measures the cavern shape detection and associated the ground equipment. Therefore, the safety analysis of salt rock gas storage in construction period is very necessary.This paper focused on the following research:① The cavern construction principle and single well convection of salt rock gas storage has been analyzed. The factors influencing the dissolution rate of mineral salt have been introduced including the intrinsic qualities such as mineral water solubility, the taste of ore, ore composition and ore structure and the external factors such as solution of motion state, the concentration of the solution, temperature and pressure, the spatial position of dissolution and the nature of the solvent.② The key influencing factors of the cavern under construction have been analyzed by the software of Salt Cavern Builder V 1.0. These key factors include cycle mode, salt rock grade, column combination, water displacement, the number of interlayer and the location of oil cushion. It can be seen from the simulation results if the improper selectiom of cavern construction process the cavern shape was irregular.③ Through an in-depth analysis on the causes of typical accident of bedded salt rock gas storage and the actual geological condition factors of Jintan gas storage under construction six aspects risk source including the salt rock and interlayer characteristics, stratigraphic characteristics, cavern design, construction control facilities and human error were analyzed. The fault tree model of salt rock gas storage under construction was established. The basic events and occurrence way were obtained by the qualitative analysis of fault tree.④ There evaluation unites were obtained according to the different nature of the risk factors which were reasonable selected. They were the mechanical parameters of salt rock, interlayer parameters and cavern parameters. The safety evaluation system of salt rock gas storage was established. The scoring models for various evaluation indicators were constructed based on the the previous experimental researcher and numerical simulation of the members of the project group.⑤ The variable weight method and relative difference function method were used to carriy out the safety comprehensive assessment. The variable weight method was used to adjust the index weight and the variable weight changed with the assessment value which highlighted the influence of individual factors on the evaluation results. The calculation result was compared with the results of the fuzzy comprehensive evaluation method and fuzzy grey correlaction method methods. The three resulta had little difference which proved the safety comprehensive evaluation method of variable weight and relative difference function had good objective and accuracy.⑥ Many optimizable factors exist in the construction period with different influencing magnitudes. The three main factors, i.e. the position of interlayer, the ratio of height to diameter and the width of pillars, are selected to be studied. The text schemes were made based on the principle of orthogonal experimental design and the related numerical simulation experiments were conducted by the COMSOL Multiphysics software. The displancement and stress of the top spot, the bottom spot, the middle spot and interlayer spot were chosen to be the experimental index. Using the extreme difference analysis and varience analysis, the results were analyzed in detail. The best sensitivity level and the optimal combination mode of each factor were determined. The values of the ratio of height to diameter and the width of pillars that were obtained from the optimal combination were put into the scoring models. The scores were 100 which verified the accuracy of numerical simulation. |
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