Browsing by Subject "poroelasticity"
Now showing 1 - 3 of 3
Results Per Page
Sort Options
Item Efficient Geomechanical Simulations of Large-Scale Naturally Fractured Reservoirs Using the Fast Multipole-Displacement Discontinuity Method (FM-DDM)(2014-04-28) Verde Salas, Alexander Jos?Geothermal and unconventional reservoirs play an important role in supplying fuel for a growing energy demand in the United States. The development of such reservoirs relies on creating a fracture network to provide flow and transport conduits during injection and production operations. The Displacement Discontinuity Method (DDM) is frequently used for modeling the behavior of fractures embedded in elastic and poroelastic rocks. However, DDM requires the calculation of the influence among all fractures being computationally inefficient for large systems of cracks. It demands quadratic and cubic complexity of memory and solution time by direct methods, respectively, limiting its application to only small-scale situations. Recent fast summation techniques such as the Fast Multipole Method (FMM) have been used to speed up the solution of several boundary element problems using modest computational resources. FMM relies in accelerating matrix-vector products in iterative methods by splitting the computation of the influences among elements into near and far-field interactions. While the former are calculated similarly to the conventional DDM, the latter, where most of the interactions are found, are efficiently approximated by the FMM using analytical multipole and local expansions. However, in spite of its immediately apparent application in the geomechanic context, FMM has been limited to only certain fracture problems because those analytical expansions are only available for selected fundamental solutions and the development for new ones requires complex mathematical derivations even for those kernels of simple form. This work presents a new method called Fast Multipole?Displacement Discontinuity Method (FM-DDM) for an efficient flow-geomechanical simulation of large-scale naturally fractured reservoirs undergoing fluid injection and extraction. The approach combines both DDM and FMM using for the latter a kernel-independent version where multipole and local expansions are not required opening a range of potential applications within the geothermal and oil industries. Several case studies involving fracture networks with up to one hundred thousands of boundary elements were presented to evaluate accuracy, computational efficiency and applications of the FMM approach. From the results, FM-DDM showed an excellent agreement with well-known benchmark solutions outperforming DDM with linear complexity in both memory and execution time. In addition, a variety of large-scale geomechanical applications were efficiently evaluated with FM-DDM involving interactions between transverse hydraulic fractures and a fracture network, fast visualization of high-resolution stress distribution, and the design of exploitation strategies in elastic and poroelastic fractured reservoirs.Item Fundamental Investigation of Pore Pressure Prediction During Drilling from the Mechanical Behavior of Rock(2011-07-18) Rivas Cardona, Juan 1980-An investigation was conducted as a preliminary effort to develop a methodology to predict pore pressure in a rock formation during drilling, for all types of rocks and situations. Specifically, it was investigated whether or not the virgin pore pressure (the pore pressure of the undisturbed rock) can be determined at the drill bit from drilling and environmental parameters, as well as solid and pore fluid properties. Several drilling situations were analyzed to develop models relating pore pressure to drilling and environmental parameters, as well as solid and pore fluid properties. Three approaches to the modeling of such drilling situations were considered, which were used to predict pore pressure and compare the predictions to actual drilling data. The first approach used the concept of the effective stress in conjunction to the Mohr-Coulomb failure criterion. The second approach used the concept of the mechanical specific energy. The third approach made use of basic principles to relating virgin pore pressure to drilling and environmental parameters, as well as solid and pore fluid properties. This third approach resulted in the proposal of a more fundamental way of viewing mechanical specific energy (MSE) and the use of Biot's poroelasticity theory to describe the cutting process of rock. The first approach did not provide an adequate prediction of virgin pore pressure for all types of rocks and situations. The second approach showed promising results with limited actual drilling data. A sensitivity analysis of the model resulting from the third approach indicated that pore pressure, type of rock, and back rake angle of the cutter are the most significant factors affecting the energy required to break the rock. Moreover, rate of cutting stress, depth of cut, and type of pore fluid become significant factors of the cutting process only when a low-porosity, low-permeability rock is considered. It was concluded that there exists a relationship among pore pressure, drilling and environmental parameters, as well as solid and pore fluid properties. Therefore, it is possible in principle to determine the virgin pore pressure at the drill bit from drilling parameters, environmental parameters, and material properties. However, further work is required to establish a quantitative relationship among the significant parameters before a methodology to predict virgin pore pressure for all types of rocks and situations can be developed.Item Geomechanical Development of Fractured Reservoirs During Gas Production(2013-04-05) Huang, JianWithin fractured reservoirs, such as tight gas reservoir, coupled processes between matrix deformation and fluid flow are very important for predicting reservoir behavior, pore pressure evolution and fracture closure. To study the coupling between gas desorption and rock matrix/fracture deformation, a poroelastic constitutive relation is developed and used for deformation of gas shale. Local continuity equation of dry gas model is developed by considering the mass conservation of gas, including both free and absorbed phases. The absorbed gas content and the sorption-induced volumetric strain are described through a Langmiur-type equation. A general porosity model that differs from other empirical correlations in the literature is developed and utilized in a finite element model to coupled gas diffusion and rock mass deformation. The dual permeability method (DPM) is implemented into the Finite Element Model (FEM) to investigate fracture deformation and closure and its impact on gas flow in naturally fractured reservoir. Within the framework of DPM, the fractured reservoir is treated as dual continuum. Two independent but overlapping meshes (or elements) are used to represent these kinds of reservoirs: one is the matrix elements used for deformation and fluid flow within matrix domain; while the other is the fracture element simulating the fluid flow only through the fractures. Both matrix and fractures are assumed to be permeable and can accomodate fluid transported. A quasi steady-state function is used to quantify the flow that is transferred between rock mass and fractures. By implementing the idea of equivalent fracture permeability and shape-factor within the transfer function into DPM, the fracture geometry and orientation are numerically considered and the complexity of the problem is well reduced. Both the normal deformation and shear dilation of fractures are considered and the stress-dependent fracture aperture can be updated in time. Further, a non-linear numerical model is constructed by implementing a poroviscoelastic model into the dual permeability (DPM)-finite element model (FEM) to investigate the coupled time-dependent viscoelastic deformation, fracture network evolution and compressible fluid flow in gas shale reservoir. The viscoelastic effect is addressed in both deviatoric and symmetric effective stresses to emphasize the effect of shear strain localization on fracture shear dilation. The new mechanical model is first verified with an analytical solution in a simple wellbore creep problem and then compared with the poroelastic solution in both wellbore and field cases.