Fluid-Solid Coupling Model And Its Numerical Simulation For Submarine Energy Soil Under Depressurizing Production

Natural Gas Hydrate(NGH)is a kind of cage-shaped ice compound formed by methane gas and water under specific temperature and pressure conditions.It is a new type of clean and strategic alternative energy with wide distribution,large reserve and high energy density.Submarine energy soil especially refers to the soil with natural gas hydrate in deep-sea environment.As a relatively economical and efficient way to extract NGH,it is a complex process involving many factors such as phase change,fluid flow and soil deformation.In the process of production,the seepage field of hydrate and the soil deformation field will couple with each other,which have various influences on the energy soil and the surrounding environment.The fluid-solid coupling model for NGH is suitable for practical engineering and it is of great significance for the safe production of NGH and the stability evaluation of submarine slope.Based on the previous research results,this research aims to establish a fluid-solid coupling model for submarine energy soil to solve it numerically,and to carry out verification and simple engineering application.This study has mainly completed the following works:(1)Based on the research results on the fluid-solid coupling theory,laboratory test and numerical simulation of energy soil,a fluid-solid coupling model for energy soil decompression mining was established,which can take into account the mass conservation,momentum conservation,hydrate decomposition dynamics and phase transition.(2)The finite element weak form of the fluid-solid coupling model is derived,and the numerical calculation of the model is realized in the COMSOL Multiphysics.The effectiveness and rationality of the model are validated by the analysis and it is compared with the one-dimensional result.Using the finite element strength reduction method and combining with the actual occurrence of hydrate,the soil deformation calculation and stability analysis of the slope of hydrate layer are realized based on the proposed fluidsolid coupling model.(3)In order to simplify the model and apply it to engineering calculation,the simplified calculation of fluid-solid coupling model was realized by independently writing USDFLD user subroutine with ABAQUS software.The sufficient computational accuracy of the simplified fluid-solid coupling model of energy soil is verified through the comparison of COMSOL with ABAQUS under the same condition.The results show that the model is simple,efficient,fast convergency and more suitable for engineering calculation with less parameters.