Progress has been made in the study of multi-field coupled numerical simulation methods for natural gas hydrates

Fluid-structure interaction simulation method of finite element and finite element hybrid of control body and its application in complex structural wells Courtesy of laboratory

Recently, researchers from the Marine Mineral Resources Evaluation and Detection Technology Functional Laboratory of the Marine Pilot National Laboratory have made new progress in the study of multi-field coupling numerical simulation methods for hydrates, and proposed a numerical simulation method based on the finite element method of the controlling body and the mixture of finite elements, which provides a new numerical simulation research method for the evaluation of the productivity and mechanical stability of hydrate mining.

The extraction of natural gas hydrates is a THMC multiphysics coupling process involving seepage, heat transfer, hydrate phase transition and mechanical deformation of sediments. From the perspective of the research object, seepage, heat transfer and hydrate phase transition can be regarded as hydrodynamic problems, while sediment deformation is a solid mechanics problem. Due to the different study objects, fluid and solid systems should be treated using different numerical methods.

At present, the hydrate THMC coupling numerical simulation method has two research ideas: the first is to use the finite volume method to calculate the fluid system, and the finite element method to treat the solid system; the second idea is to use the finite element method to process the fluid system and the solid system at the same time. However, the first method has the problem of interpolation in the fluid-structure interaction process and the mesh of the fluid system is not suitable for solid systems; the second method has the problem of local non-conservation of the fluid system, resulting in non-convergence and non-physical solution.

The new study proposes a new idea of the mixture of finite elements and finite elements of the control body, constructing a set of dual control body meshes on the basis of the all-non-structural mesh, and solving the fluid system by using the finite volume method combined with the interpolation function of the finite element on the control body mesh, while the solid system uses the finite element method on the original mesh. Such a new set of research ideas has obvious advantages, one is that the constructed control body makes the solution variables of the fluid system and the solid system are located at the same node, which avoids the problem of interpolation and mesh adaptation of the flow-structure coupling while ensuring the local conservation of the fluid system; the second is to introduce the finite element interpolation function for multi-point flow approximation, avoiding the requirements of the traditional finite volume method for mesh orthogonality, and can use a completely non-structural mesh to build a complex geometric model.

Based on the above algorithm, the team developed a set of numerical simulators with completely independent intellectual property rights, QIMGHyd-THMC, and verified the simulator using the results of indoor simulation experiments and international mainstream numerical simulation software. This study provides a new idea and framework for the numerical simulation method of multi-field coupling of hydrates.

The comparative results of the calculation results of the QIMGHyd-THMC simulator and the international mainstream simulator were published online in the top journal of geotechnical engineering, Computer and Geotechnical Engineering, entitled “Multi-field Coupled Numerical Simulation of Seepage, Heat Transfer, Phase Transition and Deformation of Natural Gas Hydrate Extraction Based on Control Body Finite Element (CVFEM) and Finite Element (FEM)”.

The research was co-funded by the Qingdao Marine Science and Technology Pilot National Laboratory marine mineral resources evaluation and detection technology function laboratory independent project, the National Natural Science Foundation of China, the Natural Science Foundation of Shandong Province and the Taishan Scholars Distinguished Expert Program. (Source: China Science Daily, Liao Yang, Gao Qian)

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