A damage model for fracking

TL;DR

This paper presents an analytical damage model for super fracking in tight shale reservoirs, linking water injection to fracture reactivation and damage zone growth, validated by typical reservoir data.

Contribution

It introduces a novel spherical damage model for super fracking that relates water volume to fracture propagation in elastic media.

Findings

Predicted water volumes match observed super fracking data.

Model captures the growth of damage zones during water injection.

Provides a theoretical basis for optimizing fracking operations.

Abstract

Injections of large volumes of water into tight shale reservoirs allows the extraction of oil and gas not previously accessible. This large volume "super" fracking induces damage that allows the oil and/or gas to flow to an extraction well. The purpose of this paper is to provide a model for understanding super fracking. We assume that water is injected from a small spherical cavity into a homogeneous elastic medium. The high pressure of the injected water generates hoop stresses that reactivate natural fractures in the tight shales. These fractures migrate outward as water is added creating a spherical shell of damaged rock. The porosity associated with these fractures is equal to the water volume injected. We obtain an analytic expression for this volume. We apply our model to a typical tight shale reservoir and show that the predicted water volumes are in good agreement with the volumes used in super fracking.