Dynamics of fluid-driven fractures across material heterogeneities

TL;DR

This study experimentally and theoretically investigates how material heterogeneities, especially stiffness contrasts in layered materials, influence the dynamics of fluid-driven fracture propagation, with implications for underground resource management.

Contribution

It provides new insights into how macroscopic heterogeneities affect fracture propagation and introduces a model coupling elastic deformation, toughness, and volume conservation.

Findings

Fracture behavior depends on the originating layer's stiffness.

Stiffness contrast influences the speed and extent of fracture propagation.

Scaling laws relate fracture geometry to material and injection parameters.

Abstract

Fracture propagation is highly sensitive to the conditions at the crack tip. In heterogeneous materials, microscale obstacles can cause propagation instabilities. Macroscopic heterogeneities modify the stress field over scales larger than the tip region. Here, we experimentally investigate the propagation of fluid-driven fractures through multilayered materials. We focus on analyzing fracture profiles formed upon injection of a low-viscosity fluid into a two-layer hydrogel block. Experimental observations highlight the influence of the originating layer on fracture dynamics. Fractures that form in the softer layer are confined, with no penetration in the stiffer layer. Conversely, fractures initiated within the stiffer layer experience rapid fluid transfer into the softer layer when reaching the interface. We report the propagation dynamics and show that they are controlled by the toughness contrast between neighboring layers, which drives fluid flow. We model the coupling between elastic deformation, material toughness, and volume conservation. After a short transient regime, scaling arguments capture the dependence of the fracture geometry on material properties, injection parameters, and time. These results show that stiffness contrast can accelerate fracture propagation and demonstrate the importance of macroscopic scale heterogeneities on fracture dynamics. These results have implications for climate mitigation strategies involving the storage of heat and carbon dioxide in stratified underground rock formations.