Gas-water displacement through fracture networks

Abstract

This study is focused on gas-water displacement through fracture networks. First, we investigated the flow patterns in fracture branches following a fracture intersection. Laboratory experiments were conducted to qualitatively identify the gas-water flow patterns in intersecting fractures. A mathematical model consistent with the actual phenomena observed in the laboratory was then formulated. The mathematical model is represented by a nonlinear system of partial differential equations, which is solved by an iterative numerical method. In the second part of the study, investigations of a vertical cross section of a fracture network were conducted. Two sets of fractures were assumed to intersect orthogonally, as characteristic of some granites. The angles of the fractures with the horizontal direction were either 45°or 135°. Fracture intersection centers, fracture lengths, and fracture openings were generated according to statistical distributions. Simulations were carried out under constant pressure boundary conditions at top and bottom as might be found at offshore radioactive repositories. The present study, which accounts for a gas-water slug, shows that the flow of water reaches quasi-steady state with continuous gas release.