| Energy reserves are of strategic importance to all countries of the world.Taking advantage of the characteristics of low permeability and good creep behavior of salt rock,The underground gas storage reservoirs for natural gas has been widely constructed in various countries.Salt-cavern gas storage reservoirs have large capcity,long service time,frequent injection and mining work and large amount of short-term throughput,therefore its safety has been paid more and more attention.By the end of 2013,there were 693 underground gas storage depots in the world,with a total work volume of 358.8 billion square meters,accounting for 11%of global natural gas consumption.In recent years,Several accidents in the salt cavern gas storage occurred frequently.The common accidents include natural gas leakage,excessive deformation of the surrounding rock in the cavity,and surface subsidence above the storage gas reservoir.Such kinds of accidents occur suddenly and could easily cause great damage.Therefore,safety assessment of the gas storage is particular important to the storage operation.Most of the salt storage gas reservoirs under construction in China are located In the economically developed areas with large population.Once the gas storage reservoir accidents occurs,it will be great threats to the safety of people's life and property.Therefore,it is necessary to evaluate the stability of the salt cavities that have been operated.This paper took chamber 1 and chamber 2 of Jintan Gas Storage as the engineering background,revivified the actual shape of the two cavities,An geomechanical model experiments of injection and mining operation of salt cavern gas storage has been conducted,and the change rules of pillar's displacement under single cycle and actual cycle of gas injection and mining operation of Jintan gas storage are obtained,Suggestions are put forward based on the analysis of experimental error.The numerical simulation results of the single cycle working conditions were compared with physical model test,Which proved the accuracy of experimental process control.And based on the actual injection and mining process data of the Jintan gas reservoir,the stability of West-1 and West-2 cavities was analyzed by numerical simulation,which provides useful reference for the safety operation of Jintan Gas Storage in the later period.This article mainly has the following research results:(1)Based on previous research,a similar material of salt rock with creep properties was formulated and made with iron fines,barite powder,quartz sand,rosin,and alcohol as raw materials,whose mechanical properties are similar to those of Jintan salt rock.the proportions are followed as salt rock:1:0.27:0.45,mudstone 1:0.67:0.45,salt rock sandwich:1:0.67:0.19.Through uniaxial compressive tests,the mechanical parameters of similar materials were obtained.the independently developed low-intensity rheometer was used to conduct uniaxial creep tests on similar materials.The creep properties of similar materials are similar to those of the original rock.(2)The Salt-hole Reservoir Full-cycle Injection and Mining Operation Monitoring and Evaluation Simulation Experiment System was developed,The roof beam of the model counter-force rack device can move and lock automatically.The hydraulic loading system which was equipped with pressure keeping and compensation device can automatically adjust and achieve the function of long-term three-dimensional gradient non-uniform loading.The gas injection and mining system can adjust and monitor the pressure inside the cavity in real-time controls the change of the pressure inside the cavity through the gas injection and production system and monitors the gas pressure value in real time,thus Simulating the real working condition in the model.(3)According to the shape of westl and west2 cavities,salt rock chamber airbags was used to simulate the actual geological condition.Strain bricks,fiber optic pressure boxes,multi-point displacement meters and rod displacement sensors were installed around the chamber and in pillar in order to monitor the regularity of displacement.Under single-cycle injection and production conditions,the radial deformation during gas production increases significantly and the stress shows an increasing trend.Due to the creep characteristics in constant pressure,the deformation around the cavity increases slowly.The waist deformation of the cavity is large,and stress concentration tends to occur at the top of the cavity.In the actual operating pressure conditions of the Jintan gas storage,frequent injection and extraction will increase the deformation rate of the salt chamber,and the lack of a regulated stage between the two gas production will cause continuous deformation of the pillar.In the later stage of operation,frequent and non-sequence injection should be avoided,as much as possible,a certain voltage stabilization phase should be added between two continuous gas production.In the process of full-cycle injection-production experiment,the data obtained by multi-point displacement meter,strain sensor and optical fiber pressure box have large errors.Through the summary of the experimental process,the cause of the error is found out and the corresponding solution proposal is proposed.as reference for future experiments.Flac3D was used to simulate single-cycle and full-cycle injection and mining operating conditions.The accuracy of numerical simulation was verified by the single-cycle test.Based on the actual injection and production gas data of the Jintan gas storage,three factors Which affect the stability comprising the salt rock itself,the stability of the pillar,and the pressure change were analyzed,Including the pillar plastic zone distribution horizontal displacement,and volumetric shrinkage calculation,the salt rock expansion safety factor was introduced to fully evaluated the stability of two adjacent salt chambers.It can provide a useful reference for the future safe operation of the gas storage. |
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