Experimental Study On Creep Behavior Of Surrounding Rock Of Gas Storage Reservoir Under Different Stress Paths

In recent years,the gas shortages,which has happened many times,in some areas it is difficult to deliver natural gas to homes in time during peak demand,which seriously influences the quality of life.With the emergence of the problem of gas consumption,the construction of underground gas storage becomes an effective method to deal with this problem.As a structural form of underground space,the underground gas storage can’t avoid structural deformation caused by creep.Creep is a crucial mechanical properties in rock,and its variation directly influences the safety and stability of underground engineering structures.With the Shuang Tuozi gas storage as an example,this paper adopts the field investigation,indoor experiment and numerical simulation to study the creep behavior with sandstone sample from 2061.86 m ～ 2061.3 m,based on the indoor test results,to carry out numerical simulation and analysis of the long-term stability of the gas storage.The main results are as following:(1)To carry out triaxial compression test with The British GDS high pressure triaxial test system.Based on the relationship between stress and strain,the rock was determined as brittle rock,and the elastic modulus and the Poisson ratio of rock were determined by the relationship curve.(2)According to the stress-strain results of triaxial compression tests,creep tests under the same confining pressure and step loading axial pressure were carried out.According to the basic design of the data,three different confining pressure to creep test,and get the creep test results with different loading paths.To analyze the strain curves with time under different stress paths,isochronous curve and the curves of creep rate with time,to get the creep deformation properties of sandstone.(3)Creep models are divided into empirical models and component models.Three basic element models are introduced in detail: elastic element,plastic element and viscous element.And five combined original models formed by combining basic component models in different ways: Maxwell model,Kelvin model,Bingham model,viscos-plastic model,and Burgers model.(4)Based on the creep test results,the deformation properties of the creep are obtained,and the deformation properties of the sandstone samples are more consistent with Burgers model.On this basis,Burgers one-dimensional creep equation and threedimensional creep equation were deduced.The Origin internal software was used to compile and identify the parameters of Burgers model,and obtain the parameters of Burgers model.Compared with the fitting curve,the fitting effect is good,which confirms that the creep deformation is similar to Burgers model.(5)FLAC 3D was used to analyze an example of Burgers model,and the simulation results are compared with the experimental results.The parameter results obtained by Origin are reasonable,and the fitting degree between experimental data and simulated data is very high.(6)FLAC 3D software was used to simulate the long-term stability of gas storage,to analyze the variation rules of top and bottom displacement under different confining pressures and different time;and calculate the volume loss under different confining pressures by Fish.By the changes of displacement and volume,it was concluded that confining pressure could restrain rock deformation.