Numerical Simulation of Shear Behavior and Permeability Evolution of Rock Joints with Variable Roughness and Infilling Thickness

Jingyi Cheng,Zhijun Wan,Hongwei Zhang

doi:10.1155/2018/1869458

Abstract

The mechanical properties and permeability evolution of sand-infilled rock joints during the shear process is an important issue in rock engineering, such as it pertains to hydraulic fractures filled with proppant. Shear can disrupt the preexisting hydraulic and mechanical equilibrium conditions, thus affecting fluid flow. In this study, we simulate the shear behavior of rock joints with variable roughness and sand infilling thickness using the discrete element code PFC2D. Rock joint roughness is evaluated by the joint roughness coefficient (JRC), and sand infilling thickness is evaluated by a thickness ratio (i.e., ratio of infill thickness to rock height) ranging from 0.02 to 0.20. The results show that peak shear strength decreases with the thickness ratio in a relation that can be expressed by a hyperbolic function. We also measure the permeability evolution during shearing and find that the permeability of infilled rock joints increases with both the thickness ratio and JRC.

Highlights

The mechanical and hydraulic properties of rock joints are of great significance in rock engineering, including near-field modeling of activated faults [1,2,3], petroleum, shale, and geothermal reservoirs [4,5,6,7,8,9]
Our numerical simulation results indicate that evolution of the shear strength and permeability of rock joints is strongly related to the infill thickness ratio (t/h) and joint roughness coefficient (JRC)
Five groups of JRCs were adopted to represent joints with different roughness, and five groups of infill thickness ratios were used to study the impact of infill thickness on the shear behavior and permeability evolution

Summary

Introduction

The mechanical and hydraulic properties of rock joints are of great significance in rock engineering, including near-field modeling of activated faults [1,2,3], petroleum, shale, and geothermal reservoirs [4,5,6,7,8,9]. Several models have been proposed to predict the peak shear strength of infilled joints by considering the ratio of infill thickness (t) to the height of an idealized (i.e., regular or planar) joint wall asperity (a) [25,26,27,28,29]. In these models, shear strength decreases with t prior to reaching the critical value t/a. Natural rock joints commonly have undulating surfaces, Geofluids (b)

Methods

Results

Conclusion