Gas-Flow Simulation in Discrete Fracture-Network Models

Abstract

Summary Advanced characterization methodologies are now able to provide realistic pictures of fracture networks. We recently developed software to simulate the transient and pseudosteady-state flows of a slightly compressible fluid in discrete fracture-network (DFN) models. This simulator is used to validate the fracture-network geometry and to calibrate the hydraulic properties of the fractures through dynamic data obtained from flowmeters, interference, and well tests. This paper is dedicated to the extension of the methodology to gas cases, taking into account the high fluid compressibility and the non-Darcy flow effects near the wellbore. The main features of our simulator are described and illustrated through demonstrative examples. Our DFN simulation approach is based on an optimized explicit representation for both matrix and fracture media and a specific treatment for matrix/fracture and matrix/matrix exchanges. A pseudopressure function is included in the diffusivity equation to take into account highly compressible fluids. The hydrodynamic behavior of gas fluid flow near the wellbore is taken into account through a skin effect proportional to the flow rate for both matrix/well and fracture/well transmissivities. This innovative numerical simulator is validated against existing analytical solutions and compared with finite-volume solutions computed with a suitable grid. Then, for application purposes, a complex realistic case involving a multiscale natural fracture network with small-scale fractures and major objects such as seismic and subseismic faults is presented. An interference test is simulated on a representative DFN model and on the equivalent dual-porosity model built thanks to upscaling procedures. This upscaled reservoir model is shown to remain consistent with the geological DFN model in terms of gas flow. This example illustrates the practical use of DFN models in our fractured-reservoir-modeling workflow.