Numerical simulations of incompressible fluid flow in synthetic fractures using lattice Boltzmann method

  • PDF / 3,542,626 Bytes
  • 16 Pages / 595.276 x 790.866 pts Page_size
  • 91 Downloads / 209 Views

DOWNLOAD

REPORT


ORIGINAL PAPER

Numerical simulations of incompressible fluid flow in synthetic fractures using lattice Boltzmann method Guan Rong 1,2,3 & Long Cheng 2,3 & Junsong Quan 2,3 & Yaosheng Tan 1 & Renhui He 2,3 & Jie Tan 2,3 Received: 20 April 2019 / Accepted: 26 October 2020 # Saudi Society for Geosciences 2020

Abstract The effect of the geometrical complexity on the fluid flow through single fractures is the subject of this study. Synthetic selfaffine fractures with different waviness and local roughness are generated by SynFrac. Several fracture profiles were sliced from the generated fractures for 2D simulations. An incompressible lattice Boltzmann method with non-equilibrium extrapolation method was used to simulate the fluid flow through the generated rough fractures by solving the full Navier-Stokes equations. The results indicate that the scaling irregular nature has a great influence on the fluid flow through single fractures. The tortuosity and the randomly distributed stagnated areas had been confirmed as the reasons for the deviation from local cubic law both theoretically and numerically. The tortuosity tends to have a linear relationship with the standard deviations which represent the amplitude of the waviness on the large scale, and a second-order dependence on the fractal dimensions which presents the degree of local roughness. The recirculation zones were formed in the troughs of rough fractures even when the flow was a creeping one with the Reynolds number below 1. These stagnated areas were observed to have an intuitive influence on the local effective advective aperture. An effective volume ratio was defined to quantify this effect of eddies on the hydraulic aperture which had been related to the local roughness of the fractures. The tortuosity of the fluid flow and eddies formed along the fractures combined together to make the permeability deviate from the local cubic law. Keywords Fracture . Flow . Roughness . Lattice Boltzmann method (LBM) . Tortuosity

Introduction It has been widely recognized that the fluid flow in fractured rock is an important issue in many geological areas such as water conservation, oil exploitation, nuclear waste disposal, and some other projects related to the highly fractured rock. It is the ubiquitous presence of fractures that makes the hydraulic behavior of rock masses different from the intact rocks as it Responsible Editor: Amjad Kallel * Guan Rong [email protected] 1

China Three Gorges Projects Development Co., Ltd, Chengdu 610041, China

2

Key Laboratory of Rock Mechanics in Hydraulic Structural Engineering, Ministry of Education, Wuhan University, Wuhan 430072, China

3

State Key Laboratory of Water Resources and Hydropower Engineering Science, Wuhan University, Wuhan 430072, China

provides the major conduits through which fluid can flow (Jaeger et al. 2007). Usually, the permeability of the rock in the field-scale is determined by the structural rock fracture, as most of the fluid flow takes place predominantly in a single fracture or a network of fracture