Computational Modeling of Fluid Flow through Fractured Media.

摘要

Mathematical and computational models were used to analyze the effect of confining pressure on permeability of fractures. These models may find application in the implementation of reservoir engineering codes to estimate the amount of carbon dioxide that can be pumped into underground geological formations under different confining pressures. Understanding the variation of fracture permeability with confining pressure is of paramount importance for effective design and operation of the geological sequestration processes, and as well as natural gas production from shale formations. These processes are typically associated with significant changes in the confining pressure.;In this thesis, first an elastic-plastic model was developed to describe the deformation and permeability of fractured rocks under confining pressure. Elastic and elastic-plastic contact models were used to analyze the deformations of a representative element containing a single fracture under various confining pressures. The present work utilizes elements from contact mechanics and viscous flows to derive an expression for permeability of fractured rocks under a range of confining pressures. The model was then used to determine permeability for different confining pressures. The model predictions were compared and discussed with the experiments.;Computational modeling of an idealized and real fracture under confining pressure was also conducted. A combination of computational fluid dynamics (CFD) and finite element (FE) models were used in the analysis of the undeformed and deformed fracture. The FE analysis incorporated elastic-plastic material nonlinearities. The models were used to develop a better understanding of fluid flow through fractures for different levels of confining pressure. Flow through the undeformed fracture was analyzed first. Then, various levels of confining pressure were imposed, and the deformed state of the fracture was computed using the FE analysis. Subsequently, the deformed states of the fracture were imported into a CFD code and the corresponding pressure drops for various flow rates and the associated details of the velocity field were evaluated.;The elastic-plastic mathematical and computational models predictions for coal permeability under loading and unloading confining pressure were compared with the experimental data reported in the literature. The results produced trends similar to the data for the range of confining pressures used in the experiments. Both of these models can be used to predict the permeability of other fractured media with different material properties.