An Integrated Discrete Fracture Model for Description of Dynamic Behavior in Fractured Reservoirs

Abstract

We present the framework for a numerical model that is capable of calculating the coupled interaction of mass transfer between fractures and surrounding matrix rock, fracture deformation, and fracture propagation. We call the framework an integrated discrete fracture model (iDFM) approach, because it is necessary to combine several numerical modeling strategies that were each developed originally to solve particular types of problems in order to capture the dynamic behavior of fractured systems appropriately. In this work, we extended the coupled fluid flow, geomechanics, and fracture propagation model introduced by McClure (2012) to incorporate mass exchange between fractures and surrounding matrix rock. We adopted a technique called hierarchical fracture modeling for the matrix-fracture mass transfer component of the model to ensure that the fracture propagation problem remained tractable in terms of numerical efficiency. In this paper, we first present the formulation for the iDFM approach. We verified the accuracy of the model against an analytical solution to a fractured reservoir problem, and subsequently characterized several of the model’s numerical properties. We found that the matrix-fracture mass transfer model was able to yield reasonably accurate solutions with only a modest increase in the total number of degrees of freedom beyond what is required to solve the fracture flow and deformation problem. The convergence rate of the matrix-fracture mass transfer model improved for low matrix permeability settings. Finally, we applied the model to a synthetic example of a minifrac analysis in a geothermal well in order to demonstrate the model’s ability to calculate complex behavior in dynamic fracture systems.