Data for "Permeability and microcrack geometry: Dynamic loading induced evolution"

Input and output files for simulations of results in:  "Permeability and microcrack geometry: Dynamic loading induced evolution".

Abstract

We propose a novel method for modeling permeability evolution in rocks, focusing on dynamic loading conditions. Accurate representation of permeability is essential for extraction and containment applications of fluids within geological strata. Several factors make this representation complex, mainly capturing the permeability response to variable dynamic loading. This difficulty is exacerbated in low-porosity brittle rocks due to their strong sensitivity to pore geometry and connectivity changes. This sensitivity causes drastic permeability and anisotropy alterations. Moreover, material heterogeneity and insufficient permeability measurements under dynamic conditions increase modeling challenges.

This work offers a permeability evolution model for high strain-rate accounting for damage via microcracking. Rock voids are represented by an evolving network of cracks. Changes in permeability are described by adjustments of crack geometric microvariables, including aperture, length, and distance. Cracks are idealized as penny-shaped features with prescribed orientations. The network's geometric response to dynamic loading affects void connectivity, fluid conductance, and preferential flow paths. We present a scalar description of permeability; however, future work will include the formulation for vector and tensor-based representations.

We analyze how different loading conditions affect permeability through the evolution of crack geometry. The study shows a strong correlation between permeability and crack length, propagation being a key factor. It also demonstrates how permeability increase can be inhibited by poor connectivity and crack closure. The model captures permeability changes of several orders of magnitude and agrees with experimental results on brittle rock at high strain rates. GeoDyn is the code of choice for implementing the new formulation.

Plain Language Summary

Permeability describes how easily fluids can move through rock. This property is critical for geothermal energy, leach mining, and underground fluid extraction. In many geological settings, rocks may experience rapid changes of loading conditions during earthquakes, blasting, or rapid excavation. Under these conditions, permeability can change dramatically. Predicting these changes is especially difficult in low-porosity rocks, where flow is controlled by small, isolated cracks. So, even minor changes in crack size, density, or connectivity can strongly affect flow.

In this work, permeability is represented by an changing network of cracks. The proposed model describes how microscopic crack opening, length, and distance evolve in response to loading conditions. These geometric changes determine how cracks are connected, how easily fluids traverse the rock, and whether flow has preferred paths.

Using our model, we show that crack growth can increase permeability by several orders of magnitude, consistent with laboratory results of brittle rocks under high strain rates. Additionally, we demonstrate that permeability rise can be limited when cracks are not sufficiently connected or when cracks close under compressive stress. We integrate the model into the numerical code GeoDyn to show permeability and porosity evolution over space and time in dynamically loaded rocks.