Multiphase, multiscale simulation of fractured reservoirs

Numerical simulation of the geometrically complex fractured reservoirs has been a major engineering challenge. The deficiencies of continuum models are often addressed using the discrete fracture network (DFN) models which represent the complex fracture geometry explicitly. The primary goal in this dissertation is to explore ways of applying the DFN methodology to solve a variety of multiphase problems in oil reservoir simulation. Three-dimensional, three-phase simulators using the control-volume finite-element scheme were used. After completing validation and fracture-property sensitivity studies, the limitation of employing the often-used Oda homogenization method was shown followed by the development of a simpler geometric scheme.;The important question of oil recovery from basement reservoirs (Type I) composed of fractures of various sizes was examined in detail. Oil recovery and breakthrough behavior of this system comprised of seismic and subseismic features were investigated for different oil distributions, permeability values, levels of heterogeneity and rate. In general having more oil distributed in smaller systems led to lower recovery and quicker breakthrough. Lower permeabilities in the subseismic features also led to lower recovery. The recovery at given pore volume of water injected was rate dependent in all of the scenarios explored, with the lower rate production leading to about 5% higher oil in place recovery. This phenomenon was consistent when viewed from the point of view of gravity number for each displacement. The mechanism of gravity-dominated oil recovery in two-phase applications was explored, and a "critical rate" concept for obtaining higher recoveries in gravity-dominated flow was developed.;A multiscale upscaling exercise was performed to match the oil recovery performance from a structured fault zone using a single feature with different sets of relative permeability curves. The effectiveness of using DFN simulations for reservoirs containing matrix and fractures (Type II) was shown using two different systems. It was shown that placing wells either in the fault zone or in the matrix can have significant impact on recovery and breakthrough behavior. It was also demonstrated that fracture networks bring apparent anisotropy, and water-flooding from one direction or the other may affect oil recovery. Fractured reservoir simulation is high-performance computing---data and file management, computation, visualization, etc. are integral components of this exercise. A workflow to facilitate creation of fracture networks, gridding and simulation, and visualization was developed. A fully integrated two-dimensional graphical user interface (java-based) was also built.