: A fully implicit method for coupled fluid flow and geomechanical deformation in fractured porous media is presented. Finite-volume and finite-element discretization schemes are used, respectively, for the flow and mechanics problems. The discrete flow and mechanics problems share the same conformal unstructured mesh. The network of natural fractures is represented explicitly in the mesh. The behavior of the fractured medium due to changes in the fluid pressure, stress, and strain fields is investigated. The methodology is validated using simple cases for which analytical solutions are available, and also using more complex "realistic" test cases.
The present work initially presents an overview and the theoretical background of the Material Point Method (MPM) and details of its numerical implementation for coupled fluid-mechanical problems. This method is particularly useful when analyzing large strain problems in solid/fluid media including coupled problems, in particular, for geomechanical and geological media. The method possesses both Eulerian and Lagrangian characteristics which makes it suitable for the solution of a number of problems especially when compared to the usual techniques such as the Finite Element Method (FEM). Using the FEM, sometimes remeshing can make the analysis of certain problems particularly cumbersome. In particular, in the present work the MPM is used firstly for the determination of the complete failure pattern of openings, from the initiation until its complete closure, in two different scales, laboratory and tunnel lengths. This problem may involve large strains and contact situations. The last example includes fluid-mechanical coupling under dynamic conditions. Here, the dynamic effects associated with the impact of a rock block in a saturated porous media in a slope is evaluated.
Conventional stability analysis of rock slopes during earthquakes is often confined to vertically propagated ground motions. One of the main reasons for the limitation is due to the lack of a rational yet simple way to apply an input motion of a specific incident angle. In this study a method of ground motion input was implemented for this application in analyzing a jointed rock slope. In a nutshell, it involved extending a problem domain by wrapping it with an elastic region and converting the incident waves into nodal forces in addition to make a boundary non-reflecting. The approach is general, but here only the plane strain problem was tackled and thus only two dimensional P-wave was considered. A jointed rock is defined by an elastic modulus, a Poisson ratio, the joint orientations and the strength of the joints. A 1:1 jointed rock slope of 30 m in height was used as the base rock slope. An El Centro record of 1979 was employed as the base ground motion. Three incident angles were considered in the analysis. Results obtained indicated that incident angles do have a significant impact on the stability of a jointed rock slope, and the severity of the impact depended on the relative orientation of the incident wave with respect to that of the joints.
This paper presents a numerical implementation of the coupled hydro-thermal-mechanical logic in the commercial code FLAC3D. The numerical model uses the Boussinesq approximation in which fluid density variations are neglected in all but the body force term of the equation of motion. The numerical solution is compared to an analytical solution (obtained using stability analysis) for a convection cell in a confined layer heated from below. Numerical simulation examples are presented to illustrate the development of various cell configurations in a layered system heated from below. The numerical model can be applied to the analysis of geothermal groundwater convection in sedimentary basins. The study of the convection mechanism is important because it provides a natural heat exchanger that can be accessed without engineered hydraulic fracturing because of high natural permeability.
This paper presents a comprehensive numerical modeling framework integrating macroscopic continuum and microscopic discontinuum numerical modeling methodologies. The continuum model is formulated on the poro-elastic-plastic theory in combination of erosion law. The discontinuum model couples discrete element method with pore-scale fluid flow model (e.g., lattice Boltzmann method). The microscopic discontinuum model can capture most primary hydromechanical physics occurring in the sand production process but its computation cost is very expensive, so it is used to develop erosion laws through performing extensive parametric study in modeling small-sized problems. The developed erosion laws are integrated into the continuum model to investigate real-sized problems. The theoretical formulations of the poromechanics and erosion laws are briefly reviewed. The discrete element – lattice Boltzmann coupling scheme is described with a couple of examples demonstrating its suitability in serving as a virtual laboratory for erosion law improvement or calibration.