Effects of intersection geometry on flow velocity interference and flow rate redistribution in furcating fractures

Abstract

Fracture intersections are an essential element of fracture networks in energy extraction. The accurate evaluation of the flow behavior at intersections in the furcating fracture is the key to describing the flow behavior of fractured reservoirs, yet fracture intersections are often oversimplified or even ignored. To fill this knowledge gap, the effect of geometric characteristics internal to the intersection was investigated based on direct numerical simulation by solving Navier-Stokes equations. Two parameters, θ1 and θ2, which are the angles between the normal inlet branch direction and the two sides of a closed triangle, are introduced to characterize the geometry of the intersection in a furcating fracture, and the role of geometrical parameters θ1 and θ2 in the interference effect and flow rate distribution is investigated. The results demonstrate that intersection geometry interferes with the fluid flow passing through the intersection to a certain range. With an increasing hydraulic gradient J and θ, the flow interference range increases. Under the conditions of these simulations (J = 10−3 – 10−2, Re = 101–102), J is linearly correlated with flow rate q, but with an increasing J and θ, the area and percentage of the low-velocity zone caused by an intersection increases leading to the enhancement of nonlinear flow. Furthermore, based on the simulation results, an empirical formula for quantifying the flow redistribution at intersections is proposed, contributing to the effectiveness and accuracy of modeling seepage in the fracture networks. Finally, the physical meanings of geometric parameters θ1 and θ2 are determined. This study advances the understanding of flow behavior at intersections commonly observed in discrete fracture networks from a fresh perspective, despite the difficulty of monitoring.