Bernhard Hustedt

Modelling Induced Fracture Mechanics in Reservoir Simulations – A New Coupled Simulator

Water-injection induced fractures are key factors influencing successful waterflooding projects. Controlling the dynamic fracture growth can lead to largely improved water management strategies and potentially to increased oil recovery and reduced operational costs (reduction in well count and water treatment facilities etc.). The primary tool that a reservoir engineer requires to design an optimal waterflood is an appropriate reservoir simulator that is capable of handling the dynamic fracturing process in complex reservoir simulation grids. We have developed a new modelling strategy that adds fracture-growth to our standard fluid-flow reservoir simulator. A first prototype simulator was successfully tested and applied to field cases. The dynamic fractures are free to propagate asymmetrically in length-, height-, and width-direction controlled by the pressures and poro- and thermo-elastic stresses acting on the fracture face. The stresses are calculated in the reservoir simulation grid. The simulator determines new fracture sizes by evaluating fracture propagation criteria, based on a Barenblatt condition on the four fracture tips: left, right, up, and down, and on a volume-balance on the width. This non-linear five-dimensional coupled set of equations is solved every timestep using a Broyden approach moderated with Levenberg-Marquardt techniques to handle non-linearities. Since the changing fracture sizes affect the pressure and stress profiles in the reservoir, the equations are solved in an implicit scheme.