Three Dimensional Stress Maps of Dynamic Hydraulic Fracture within Heavily Cross-Linked Hydrogels

Abstract:

Hydraulic fractures (HFs) of oil and gas shales occur miles underground, below complex, layered heterogeneous rocks making any measurements of their dynamics, extent, or structure difficult to impossible. As such, model lab systems such as blocks of PMMA or rocks fractured with air or fluid (Bunger et al [2013], Alpern et al [2012]) are studied in order to understand the intricacies of HFs. However, due to the extreme energies necessary to fracture these materials the experiments are difficult, have little flexibility in the materials, and offer little no measure of the dynamics of the fracture. Heavily cross-linked hydrogels have been shown to be a good model to study brittle fracture (Livne et al [2004]). I will discuss a new system, which we have developed to study HFs within tough hydrogels which have the benefits of having highly tunable rheology, being optically clear, and having slower fracture speeds and breakdown pressures. By embedding fluorescent tracer particles within the gel together with laser sheet microscopy, we obtain the three dimensional stress and strain maps of the zone surrounding a hydraulic fracture tip.