Study On Strength And Deformation Behaviors Of Argillaceous Silty Hydrate Sediments

The deep-sea hydrate-bearing sediments refers to the deep-sea sediment soil containing natural gas hydrate.Natural gas hydrate(NGH)is an important and new type of clean energy with large reserves,wide distribution and high energy density,which is considered as the most promising new energy for commercial development.However,the exploitation of NGH may lead to the weakening of reservoir cementation and strength attenuation,which will lead to the decrease of reservoir bearing capacity,reservoir subsidence and deformation,and may even induce shaft wall collapse,submarine landslide,methane leakage and other engineering geological disasters,which will have a serious impact on the earth's ecological environment.The hydrate reservoir in the northern South China Sea is dominated by argillaceous silt.It is an important task to comprehensively evaluate the mechanical properties of argillaceous silt hydrate-bearing sediments in the safe exploitation of natural gas hydrate in China.In this paper,the triaxial shear tests of deep-sea hydrate-bearing sediments with muddy silt sand are carried out,and the stress-strain constitutive relationship is studied by using the obtained test data,in order to provide theoretical basis for the safe exploitation of natural gas hydrate.The work carried out and the main conclusions obtained are as follows:(1)According to the physical indexes and particle size distribution curve of hydrate-bearing sediments in Shen-hu area of South China Sea,the argillaceous silt with similar particle size distribution was prepared in the laboratory as the occurrence framework of methane hydrate.Using the ETAS static triaxial test system of high pressure and low temperature hydrate produced by GDS Company in the UK,the samples of argillaceous silt sand were synthesized by in-situ formation method.(2)A total of 48 groups of triaxial shear tests were carried out to study the effects of hydrate saturation,effective confining pressure and clay content on the deformation and strength of deep-sea hydrate-bearing sediments.The test results were sorted out and analyzed,and the test results showed that:(1)With the increase of hydrate saturation and effective confining pressure,the strength and stiffness of argillaceous silt hydrate-bearing sediments increase,and it tends to show strain softening characteristics at low confining pressure and high hydrate saturation.(2)The cohesion of argillaceous silt hydrate-bearing sediments increases with the increase of hydrate saturation and clay content,but the difference between internal friction angle are not obvious,which increases slightly with the increase of hydrate saturation and decreases slightly with the increase of clay content.(3)Based on the stress-strain rule of silty sand hydrate-bearing sediments obtained from the test,Mohr-Coulomb strength criterion and Weibull distribution theory were used to determine the strength of silty sand hydrate-bearing sediments microelement,and Duncan-Chang model was used to describe the stress-strain relationship of lossless materials.Meanwhile,the existing damage model was improved and compared with the test data.It is shown that the model can better describe the mechanical properties of argillaceous silt hydrate-bearing sediments under different hydrate saturation and different effective confining pressures,which verifies the rationality and effectiveness of the model.