A Seepage-Stress Coupling Model in Fractured Porous Media Based on XFEM

Large cracks are important seepage channels inside fractured-vuggy reservoirs. Therefore, in this thesis, the calculation method of fully coupled modeling of the fractured saturated porous medium based on the extended finite element method (XFEM) is established to study the expanding regularity of cracks in fractured-vuggy reservoirs. Fully coupled governing equations are developed for hydro-mechanical analysis of deforming porous medium with fractures based on the stress balance equation, the seepage continuity equation and the effective stress principle. The final nonlinear fully coupled equations reflect not only the coupling effect of the physical quantity within the porous medium but also the coupling between the medium and the fracture. During the spatial dispersion of coupled equations based on XFEM, two kinds of additional displacement functions are introduced in the displacement model of the fracture area to reflect the strong discontinuity of the fracture surface. The pore pressure enhancement function is also applied to represent the weak discontinuous features of the normal pore pressure. The validity and efficiency of this model and calculation are verified through three calculating examples. The following crack propagation laws are obtained: (1) The larger the water flow rate is, the longer the crack propagation length is, and the larger the propagation width is (2) The greater the crack angle and the crack length, the easier it is to expand the crack. Besides, compared with dip angle, the crack length has a more sensitive influence to the crack propagation. (3) When multiple cracks exist, the larger the fracture spacing is, the easier the crack will expand.