Geophysical and Geochemical Analyses of Flow and Deformation in Fractured Rock

Open Access
Author:
Taron, Joshua
Graduate Program:
Energy and Geo-Environmental Engineering
Degree:
Doctor of Philosophy
Document Type:
Dissertation
Date of Defense:
August 17, 2009
Committee Members:
  • Derek Elsworth, Dissertation Advisor
  • Derek Elsworth, Committee Chair
  • James David Kubicki, Committee Member
  • Chris Marone, Committee Member
  • Demian Saffer, Committee Member
  • Barry Voight, Committee Member
Keywords:
  • permeability
  • rock fracture
  • fractured reservoir simulation
  • geothermal
  • volcanic dome
  • chemical creep
Abstract:
The following is a study of fluid flow and deformation in fractured rock, with particular emphasis on environments under thermal and chemical stress. Fractures are treated in the greatest detail, with constitutive modeling at pore and reservoir scale, and their impact explored with reservoir scale numerical simulation. Part I (Chapters I-IV) explores the behavior of engineered systems pushed far from equilibrium and highlights feedbacks between stress and chemistry on the evolution of the mechanical and transport properties of rocks; these observations and analyses are focused on the behavior of geothermal reservoirs. Part II (Chapters V-VI) examines the response to natural forcing and follows the complex interactions that shape processes in volcanic environments. Chapter I introduces a simulator to examine thermal, hydrologic, mechanical, and chemical processes (THMC) in deformable, fractured porous media. The combined influence of stress-enhanced dissolution, thermal-hydro-mechanical asperity strain, and mineral reaction alter the permeability of fractures during thermal, hydraulic, and chemical stimulation. Chapter II examines a prototypical enhanced geothermal system (EGS) for the relative, temporal arrival of hydro-mechanical vs. thermo-mechanical vs. chemical changes in fluid transmission as cold water is injected at geochemical disequilibrium within a heated reservoir. Chapter III develops a relationship to examine dissolution precipitation creep in crustal rocks with implicit coupling of the dissolution-diffusion-precipitation system. Long-term compaction, previously ill-constrained, is explored with two alternate methods. Chapter IV presents a model to represent these permeability change mechanisms as innately hysteretic and interlinked processes in rough contacting fractures. This model is incorporated into the numerical simulator of Chapters I and II and applied to a candidate engineered geothermal reservoir system (EGS). Utilizing a several year history of rainfall, seismic, and magma effux records, Chapter V presents a limit-equilibrium model for rainfall infiltration into a hot lava carapace to evolve stability of the dome at Soufrière Hills Volcano (SHV). Model predictions are compared to observed dome collapse events from 2000-2002. In Chapter VI histories of magma efflux and surface deformation are utilized to geodetically image magma transfer within the deep crustal plumbing system of SHV. Magma efflux is constrained with wide-aperture geodetic data to supplement a well-documented extrusion record, and these are used to explore the role of deeply sourced fluxes on short-term eruption periodicity.