Assessment of fracture characteristics controlling fluid flow performance in discrete fracture networks (DFN)
Fractures play a crucial role in earth resource engineering, such as geothermal exploitation, coalbed methane (CBM) extraction, and hydraulic fracturing. Breaches, as main channels of fluid flow, have various characteristics, such as aperture, density, and persistence that could affect the transmissivity. Due to the difficulty of distinguishing the contribution of fracture parameters to fluid flow in fractured coal and rock mass, the numerical simulation is necessary to simulate the fluid flow in fractures versus benchmarks to obtain realistic data to study the variation of flow rate with fracture parameters. In this paper, a numerical discrete element method (DEM) was used to rebuild the spatial distribution of DFN and simulate the fluid flow in DFN modeling, and the results were compared to the field test results in Yilgarn area in Western Australia. On this basis, the dependences of the flow rate on fracture parameters were obtained. In DFN modeling, the flow path was considered with a rectangular section, and its geometry was determined by aperture and persistence. As a circular fracture, its persistence is an influential factor of flow lengths. Besides, the flow channels and length in fractured coal and rock mass increased with the increase of fracture density. According to the cubic law, the flow rate has a direct relationship with the fracture opening, and the number of channels, but has an inverse relationship with the flow length, which is consistent with the simulation results. Results showed that the flow rate increased with the fracture aperture. Meanwhile, the increase of flow rate with fracture persistence was non-linear. When the size of the fracture was small, the flow rate increased gradually. However, with the rise of fracture size, the flux increased abruptly. Finally, the flow rate fluctuated with increasing fracture density. This research will enhance the knowledge of earth resource extraction performance such as CBM, geothermal, oil and in-suit leaching through the fractured media.
Keywords: Fracture characteristics, DEM, DFN, Fracture flow, Flow rate, Rock mass permeability,