Imaging elastodynamic and hydraulic properties of fractured rock: Exploring effects of dynamic stressing, shearing, fracture aperture, and roughness
Open Access
- Author:
- Wood, Clay
- Graduate Program:
- Geosciences
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- March 18, 2024
- Committee Members:
- Chris Marone, Co-Chair & Dissertation Advisor
Parisa Shokouhi, Co-Chair, Outside Field Member & Dissertation Advisor
Derek Elsworth, Outside Unit & Field Member
Tieyuan Zhu, Major Field Member
Donald Fisher, Program Head/Chair - Keywords:
- Fracture mechanics
poromechanics
nonlinear elasticity - Abstract:
- Dynamic perturbations in the subsurface, originating from natural or industrial sources, are associated with observations of changes in poro-elastic properties that have far-ranging effects. Broadly, there are "strain-induced" and "fluid-induced" sources of these subsurface perturbations and, importantly, they produce coupled phenomenological observations. Many experimental and numerical studies that quantify elastic and hydraulic properties of rock, fractured (or ``intact'') under static stress conditions, however these measures are not necessarily indicative of their response during dynamic stress conditions. Motivated by these field observations, I use simultaneous continuous fluid flow and ultrasonic monitoring to quantify the elastic and permeability changes of natural and rough fractures. Furthermore, I incorporate measures of fracture topology and contact area to connect to the spatially variable ultrasonic monitoring and as inputs for multiphysics modeling of a single planar fracture. In this dissertation, I ask fundamental questions surrounding the connection between fracture specific stiffness and fluid transport under a range of loading conditions and dynamic stressing. Moreover, I do so by performing complex experiments under triaxial stresses and use simultaneous continuous active-source ultrasonic monitoring and fluid flux measurements to measure the static and dynamic elastic and hydraulic properties of fractures. These unique experiments are also complemented by post-surface and topography characterization using pressure registering films and profilometry. I begin this dissertation by introducing the problem statement broadly and providing some context for field-scale observations of dynamic stress-induced changes in the subsurface and lay out the limitation of linear elastic work within this context. In Chapter 2, I use ultrasonic monitoring to image the spatial and elastic variability across an in-situ fractured rock specimen and relate these to fluid flow. These experiments produced complex results which highlights the variable nature of sheared fractured rock. In Chapters 3 and 4, I extend the work of Chapter 1 by focusing on the effect of stress state on dynamic stress-induced changes in flow and elasticity. Chapter 3 demonstrates the systematic reduction in nonlinear elasticity and permeability enhancement with increasing stress state, simulating depths. I additionally relate the real contact area from pressure sensitive films to the documented elastodynamic changes. Chapter 4 leverages the experimental results from Chapter 3 and utilizes high-resolution profilometry of the tensile fracture specimen as an input for multiphysics modeling. I demonstrate that perfectly matched fracture surfaces can reproduce some of the static fluid flow properties and that misalignment is highly influential on overall poro-elastic properties. Chapter 5 represents a focused study on the relation between roughness and granular in-fill of planar fractures and their influence on elastodynamic and hydraulic changes.