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Thermo-Hydro-Mechanical-Chemical Modeling of Fractured Porous Media using XFEM Technique

Mortazavi, Mohammad Sadegh | 2023

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 56536 (09)
  4. University: Sharif University of Technology
  5. Department: Civil Engineering
  6. Advisor(s): Khoei, Amir Reza
  7. Abstract:
  8. In this research, a comprehensive numerical model for Thermo-Hydro-Mechanical and Chemical multiphysics problems in fractured porous media was introduced using the eXtended Finite Element Method (XFEM), and its efficiency was demonstrated in two-dimensional problems. For the simplicity of the formulation and according to the common assumptions in the corresponding fields of study, the solid phase was assumed linear elastic and the flow was taken into account via Darcy's law. The system of governing equations comprised the linear momentum balance of the solid phase, mass conservation of pore fluids, thermal energy balance, and mass conservation of chemical species. The coupling of these equations varies in different applications; therefore, the flexibility and accuracy of the model was shown by presenting a limited number of its applications. Those applications were as follows: dynamic propagation of hydraulic fracture in saturated porous media (Hydro-Mechanical), non-isothermal two-phase flow in fractured media with or without crack propagation (Thermo-Hydro-Mechanical with two-phase flow), energy extraction from Enhanced Geothermal Systems by assuming different patterns of fractures and Non-Local Thermal Equilibrium (Thermo-Hydro-Mechanical with two temperature fields), and finally, fracture aperture alteration due to Free-Face reaction and Pressure Solution of quartz (Thermo-Hydro-Mechanical and Chemical). The common aspect of the different parts of this research was the extension of XFEM to new applications of multiphysics problems in fractured porous media. Moreover, additional options required by each field of study were added to the model. Another feature of this research was the numerous validations carried out to show the model's accuracy. In addition, the analyzes and conclusions presented for the case studies in each chapter have interesting findings in their respective fields that should be viewed independently. Simulations of Thermo-Hydro-Mechanical and Chemical coupled processes in porous media are employed in various industrial fields; such as Enhanced Geothermal Systems, oil and gas industries, nuclear waste disposal, serviceability assessment of concrete structures exposed to chemical degradation, and long-term environmental impacts. However, due to the development of new industrial fields in recent years such as CO2 sequestration, methane gas extraction from coal mines, technics of increasing permeability using acids, and low-temperature geothermal energy exploitations, new applications are being found for them increasingly. Nowadays, due to the time and budget constraints, various coupled processes are ignored in the in industrial simulations, and the resulting accuracy-loss is compensated using factors of safety. On the other hand, computer hardware is getting incredibly faster and even chipper over time, and in the near future, running complex and costly models will be justified in most fields. Therefore, it is necessary to develop more advanced numerical models. The presence of fractures in porous media changes the flow and transfer patterns. The investigation of these patterns is done more precisely by discrete fracture models. Assuming permeable fractures, they cause discontinuities in the displacement field of the solid phase and the gradient fileds of the fluid pressure, temperature, and aqueous species’ concentration. Standard FEM-based models require mesh adaptivity to account for the discontinuity geometry, which is not the case in the XFEM; therefore, this method can be a powerful solution to several kinds of discontinuous problems. Accordingly, the applicability and accuracy of the XFEM was shown in this research for various problems of fractured porous media
  9. Keywords:
  10. Fractured Porous Media ; Extended Finite Element Method ; Cohesive Crack Model ; Enhanced Geothermal Systems ; Multiphysics Modeling ; Coupled Thermo-Hydro-Mechanical-Chemical Modeling

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