| This thesis is a detailed investigation of hydraulically-driven fracture propagation in poroelastic rock. Biot's theory of poroelasticity is used to study coupling between rock deformation and fluid flow within its mass. The topic is developed as follows: (1) a nonlinear fracture mechanics model is adapted for a poroelastic continuum, (2) poroelastic concepts and effects are illustrated through application to the 1-D, PKN fracture model, (3) a 2-D, plane strain, numerical model for hydraulic fracture in poroelastic materials is described and verified, (4) a specialized code for 3-D visualization of coupled processes, using computer graphics, is presented, and (5) the plane strain model and visualization capabilities are used to further investigate a variety of poroelastic effects.; The plane strain numerical model solves three sets of fully-coupled equations representing (1) equilibrium of the rock mass, (2) conservation of fluid mass within the rock matrix, and (3) conservation of fluid mass in the fracture. The first two sets of equations are derived from a finite element approximation to Biot's theory of poroelasticity, while the third set is approximated by a finite difference model. An equilibrium fracture model is incorporated in a manner that produces a crack length that is a natural product of the solution procedure, and allows modeling of fracture initiation from a borehole. An iterative, staggered solution procedure, which implicitly advances the solution at each time step, has been designed to take advantage of vector processing on a mini-supercomputer. Images from a specially developed, workstation-based, 3D visualization tool are found to be an effective means of communicating the results and physics of coupled processes.; The primary application of this work is hydraulic fracturing in oil or gas bearing rock. Poroelastic effects on the PKN and CGDD models are investigated, along with effects on mini-frac tests which can be used to determine a variety of relevant material and fracture parameters. These latter studies include detailed simulations of fracture closure which can occur after flow into the fracture is shut-in. The results may also be applicable to dredging, drilling and cutting of fluid saturated rock. |
