Redirection of a crack driven by viscous fluid

TL;DR

This paper investigates how viscous fluid-induced shear stresses influence crack propagation directions in hydraulic fractures, revealing that the effect is negligible for tough materials but significant for brittle ones, especially in viscosity-dominated regimes.

Contribution

It analyzes the impact of hydraulically induced shear stress on crack direction criteria, comparing MCS and MSED, and highlights the significance of stress intensity ratios in viscosity-dominated regimes.

Findings

Hydraulically induced shear stress has negligible effect for high toughness materials.

Significant influence of shear stress on crack direction in low toughness, viscosity-dominated regimes.

Redirection angles depend heavily on stress intensity factor ratios.

Abstract

As shown by Wrobel et al. (2017), the hydraulically induced tangential traction on fracture walls changes local displacement and stress fields. This resulted in the formulation of a new hydraulic fracture (HF) propagation condition based on the critical value of the energy release rate that accounts for the hydraulically-induced shear stress. Therefore it is clear that the crack direction criteria, which depend on the tip distributions of the stress and strain fields, need to be changed. We analyse the two commonly used criteria, one based on the maximum circumferential stress (MCS) and another - on the minimum strain energy density (MSED). We show that the impact of the hydraulically induced shear stress on the direction of the crack propagation is negligible in the case of large material resistance to fracture, while for small toughness the effect is significant. Moreover, values of the redirection angles, corresponding to the so-called viscosity dominated regime, depend dramatically on the ratios of the stress intensity factors.