Numerical Simulation for Rock Fracture Viscoelastic Creep under Dry Conditions

Hao Kang,Stephen Brown,Herbert Einstein,John Germaine,Yanlin Zhao

doi:10.1155/2020/8879890

Abstract

In many rock engineering projects such as hydrocarbon extraction and geothermal energy utilization, the hydraulic and mechanical behavior of rock fractures significantly affects the safety and profitability of the project. In field conditions, the hydraulic and mechanical behavior of rock fractures changes with time (the rock fractures creep), and this creep is not negligible even under dry conditions. In addition, creep is strongly affected by the rock fracture surface geometry. However, there is not much literature systematically studying the effect of surface geometry on rock fracture creep under dry conditions. This paper presents the results of a numerical study considering the effect of surface geometry on rough fracture viscoelastic deformations. An in-house numerical code has been developed to simulate the viscoelastic deformation of rough fractures. In addition, another numerical code has been developed to generate synthetic rough fracture surfaces by systematically changing the surface roughness parameters: the Hurst exponent, mismatch length, and root mean square roughness. The results indicate that by increasing the Hurst exponent or decreasing the mismatch length or decreasing the root mean square roughness, the fracture mean aperture decreases, and the contact ratio (number of contacting cells/total number of cells) increases faster with time.

Highlights

In many rock engineering projects such as hydrocarbon extraction, geothermal energy utilization, or nuclear waste storage, the hydraulic and mechanical behavior of rock fractures has a strong effect on the safety and profitability of the project
The following parameters are defined: (1) Macroscopic stress σ1 = F/A, where F is the total force applied on the fracture surface and A is the area of the fracture surface (10 mm ∗ 10 mm)
The initial values of the average aperture and contact area correspond to the elastic deformation

Summary

Introduction

In many rock engineering projects such as hydrocarbon extraction, geothermal energy utilization, or nuclear waste storage, the hydraulic and mechanical behavior of rock fractures has a strong effect on the safety and profitability of the project. The deformation with time under constant stress, occurs in many types of rocks. Creep rate (i.e., the change of deformation with time) may accelerate, stay constant, or decelerate. Such creep mechanisms often occur in rock fractures, essentially involving a time-dependent change of aperture under constant load. In time, affects hydraulic conductivity and affects the safety and profitability of rock engineering projects, there is significant interest in understanding the creep behavior of rock fractures

Methods

Results

Discussion

Conclusion