Triaxial creep tests and the visco-elastic-plastic constitutive model of hydrate formations

Abstract

To study the creep properties of hydrate formations, triaxial mechanical tests and triaxial creep tests were conducted on hydrate-bearing samples. In addition, a visco-elastic-plastic constitutive model suitable for hydrate formation was established. Research results show that the higher the hydrate saturation, the stronger the cementation between skeletal particles. and the shear and crushing of the hydrate crystal during the loading process will increase the friction between the particles. As the hydrate saturation increases from 0 to 0.618, the cohesion of the samples increases from 0.4 MPa to 1.3 MPa; the angle of internal friction increases from 34.33° to 37.3°; and the long-term strength level increases from 0.5752 to 0.5866. When shear stress is lower than the long-term strength, the samples show attenuated creep characteristics, and the samples exhibit accelerated creep and constant visco-plastic deformation when higher than the long-term strength. Under identical shear stress, lower hydrate saturation corresponds to greater creep deformation of the samples. When the shear stress levels are close to strength, higher hydrate saturation corresponds to a faster accelerated creep rate. By connecting the elastic element, Kelvin element, and nonlinear viscous element in series, a viscoelastic model to describe the entire attenuated creep process of the hydrate-bearing samples is obtained. By linking the attenuated creep model with the nonlinear Newtonian element in series, a visco-elastic‒plastic model to describe the accelerated creep process of the samples is established. Compared with the test results, the calculation results of the models show a maximum error of only 7.12%.