A STUDY ON THE CONSTITUTIVE MODELING OF THE INTERBEDDED HYDRATE-BEARING SEDIMENTS

Advancing gas hydrate exploitation is one of the most important tasks for China's future energy strategy. The interbedded formation of hydrate-bearing sediments is a common feature in many target production regions. However,the hydrate gas production process disturbs the hydrate-bearing sediment,which induces shear strain to mobilise the reservoir stability and severely restrain the safe exploitation of hydrate resources. The existing constitutive characterization of hydrate-bearing sediments is mainly based on the assumption of homogeneous and isotropic material properties,and without a proper constitutive characterization method to consider the strong non-linear mechanical properties of hydrate-bearing sediments affected by the interbedded formation,that leads to inaccurate estimation of the stress and strain responses of the target production region. This study uses the homogenization theory to construct the macro and mesoscopic control equations of interbedded sediments. Based on the elastic-plastic stiffness matrix of each layer of sediments,a constitutive model for interbedded hydrate-bearing sediments was established. Sediment model parameters representing each layer within a representative volume element can be obtained based on triaxial test results of homogeneous hydrate-bearing sediment samples. By comparing the prediction results of the proposed constitutive model with the stress-strain results of the interbedded sediment triaxial test and numerical simulation,the proposed constitutive model can accurately describe the mechanical behavior of interbedded hydrate-bearing sediments in the in-situ reservoirs.