Laboratory Studies of Permeability Evolution: Roles of Fracture, Shear, Dynamic Stressing, and Reservoir Rock Properties
Open Access
- Graduate Program:
- Geosciences
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- July 27, 2018
- Committee Members:
- Chris Marone, Dissertation Advisor
- Chris J Marone, Committee Chair
- Derek Elsworth, Committee Member
- Sridhar Anandakrishnan, Committee Member
- Shimin Liu, Outside Member
- Keywords:
- permeability evolution
- permeability
- dynamic stressing
- fracture
- shear
- permeability enhancement
- Abstract:
- Fault and fracture permeability-stability relationships continually evolve over the seismic cycle. Both static and dynamic changes in mechanical stresses can affect the fluid pressures and vice versa. These changes can be potentially beneficial to energy production, as dynamic stressing has been observed to enhance reservoir permeability in natural and manufactured systems. However, both dynamic and static changes in stress have also been shown to destabilize faults, triggering earthquakes. It is clear a fundamental understanding of controlling mechanisms is necessary for safely enhancing reservoir productivity and understanding seismic hazard assessment. In this dissertation, I strive to illuminate the underlying mechanisms that govern permeability evolution, including transient changes in permeability associated with dynamic stressing and fault shear. While the relationships between fault slip, dynamic stressing, and permeability have been studied separately, little data are available on their combined effects. In each chapter, I present results from suites of carefully controlled laboratory experiments to investigate the effect of mode II fault failure and shear on permeability and poromechanical properties. In Chapter 1, I investigate the effects of dynamic stressing on highly porous reservoir rock, Berea sandstone, at various stages of shear displacement. I demonstrate that porous rock is sensitive to dynamic stressing only via fluid pulsing and that both reservoir permeability and sensitivity to dynamic stressing declines with shear. Chapter 2 extends this work into low porosity, low permeability reservoir rock, Westerly granite and Green River shale. Here I show that frequency of imposed fluid oscillations has the greatest control over permeability enhancement. Finally, chapter 3 focuses on friction and permeability responses across multiple reservoir rock types throughout the seismic cycle, simulated via Slide-Hold-Slide and velocity step testing. Here, I use in situ fractured samples alongside traditional, saw cut samples to highlight the effect of fracture roughness on the fluid response across varying rock mineralogy. This dissertation provides insight to the controlling mechanisms and data that can be used to predict reservoir behavior, including the feasibility of shear failure and dynamic stressing as reservoir permeability management techniques. I demonstrate that permeability-stability relationships evolve as a result of dynamic stressing and are dependent upon properties of the reservoir: porosity, fracture roughness, and stiffness as well as the properties of imposed dynamic stressing: frequency and amplitude. The evidence provided shows differing results from exercising the same mechanism when applied to different types of reservoir rock.