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Modeling of Hydraulic Fracturing in Fractured Saturated Porous Media Using the Extended Finite Element Method

Vahhab, Mohammad | 2015

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 47140 (09)
  4. University: Sharif University of Technology
  5. Department: Civil Engineering
  6. Advisor(s): Khoei, Amir Reza
  7. Abstract:
  8. In current study, we investigate crack propagation is saturated porous media by using the extended finite element method. The porous media is simulated by using well-known u-p formulation. In this regard the equilibrium equation of the bulk is employed together with momentum and mass balance equations of the fluid phase. The XFEM, known as one of the best methods in crack simulations, will be employed for numerical modelings. According to the method, crack propagation does not involve any changes in meshing, yet by using the concept of enrichment the elements are enabled to possess crack interfaces inside themselves. Thus by crack growth, only discritization alters and new DOFs are inserted into the solution field. The existence of discontinuities in the medium reproduces pathes with higher permeability for the fluid phase. Therefore the effects of crack in fluid phase, causes especial discontinuities known as weak one. The fluid flow within the crack is one of the most challenging issues in the study of fractured media, which causes leak-off flow along the crack interface. The fluid flow through the cavity, depending upon the natural viscosity of the fluid, faces pressure losses. Many researches have ignored this effect for simplicity of implementation, assuming a constant pressure distribution for the flow along the fracture. On the other hand, using the cubinc law the flow through the cavity could be studied more precisely and the viscosity effects to be included in simulations. This law is defined versus fluid flow along parallel plates, and by using some modification factor, has been widely used for numerical modeling of fluid flow thorugh fractures. In two phase problems, considering complexities exerted due to interaction between fluid and solid phases, there might occur contact between faces of the cracks. In solid phase, by using the contact constraints, overlap between edges of the crack is prevented. In this regard the Penalty and LATIN methods have been employed. It is knoteworthy to mention that in fluid phase, contact ends in no leak-off flow from the cavity into the domain, which is prevented by using suitable contact constraints. Hydraulic fracturing is one of the most applied procedures in improving the permeability of porous medias, which has been employed for many applications. Due to the brittle nature of the porous mediums, there could be so many faults within the domain. Thus the interaction between such faults with hydraulic fracture is needed to be studied precisely. Different scenarios has been observed for this interaction. By explaining the exact mechanical behavior ccurring in different interaction scenarios, it will be shown that there could be even happen a mixed series of these scenerios, too. In this regard crack intersections will be simulated by using new enrichment functions. The results will represent the need for coupled simulation of hydraulic fracturing procedure
  9. Keywords:
  10. Crack Growth ; Saturated Porous Medium ; Extended Finite Element Method ; Two Phase Medium ; Fractures Interaction

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