Numerical study of nonlinear fluid flow behavior in natural fractures adjacent to porous medium

Abstract

It is essential to understand the hydraulic aperture behavior of rock fractures where fluid passes through the rock mass. The geometric parameters of fracture, such as wall roughness and fracture aperture, have a significant effect on its hydro-mechanical behavior. This issue has been addressed in many papers, but the fluid passage through the permeable zone adjacent to the fracture has rarely been studied. Therefore, this paper numerically simulated the fluid behavior in the porous fractured medium. For preparing the model geometry, the 3D scanning of fracture walls was used for the samples taken from one of the oil wells in southern Iran. The geometry of fractures was prepared using ICEM CFD software, and the fluid flow in rock fracture and porous matrix was simulated with Ansys Fluent™ software. Given that the two fracture surfaces are connected in reality, the geometry of the model was constructed when the fractures are mated and the connection is established at a certain level (the connection between the two surfaces equal to 15, 30, 45, 60, 75, and 90% of the total area). The results of this simulation showed that the Forchheimer macroscopic relation well describes the nonlinear fluid flow in the rock fracture even considering the permeable matrix. However, the higher the permeability value of the matrix adjacent to the fracture, the higher the fracture permeability value. The results indicated an exponential relationship between the increased permeability and the decreased Forchheimer coefficients, which confirms the easier passage of fluid through the fracture enclosed by a zone of higher permeability. Also, the values of linear and nonlinear coefficients of Forchheimer equation were estimated for each of the geometric models, which showed that the changes in Forchheimer coefficients are exponentially related to the change in the connected surface area. • Joint permeability measurement adjusted to matrix permeability. • Forchhimeir Parameters calculation. • Optimization of fluid flow in rough joints. • Effect of adjusted permeability on fluid flow behavior.