Porosity evolution in the Newberry volcano geothermal system, Oregon, USA : feedback between deformation and alteration

• Main Author: Fetterman, James Andrew
• Other Authors: Háskólinn á Akureyri
• Format: Thesis
• Language: English
• Published: 2011
• Subjects: RES. The School for Renewable Energy Science; Renewable energy sources; Meistaraprófsritgerðir; Orkumál; Akureyri
• Online Access: http://hdl.handle.net/1946/7748

Verkefnið er unnið í tengslum við Háskóla Íslands og Háskólann á Akureyri This study attempts to quantify a relationship between 1) fracture porosity, 2) deformation and 3) mineral precipitation and hydrothermal alteration in crystalline basaltic rock from Newberry Volcano in Oregon. It attempts to find a quantifiable set of restraints for these three factors that will maximize potential for permeability enhancement of low-porosity rock using Engineered Geothermal Systems (EGS) technology. Porosity of selected samples is mapped in hand sample and microscopically using petrographic analysis with thin sections. Mineralogy is mapped through hand-sample mapping, petrographic analysis and XRD analysis. The transport of elements due to fluid flow is quantified through XRF analysis. The generation of skeletal and open porosity through dilation is explored in two end member systems, non-clay and clay-dominated fractures. Data gathered in this study suggests that both systems evolve and grow in complexity via the same processes up until a critical stage in fracture evolution. In early stages of fracture evolution, both the create porosity via dilation during slip, into which geofluids can precipitate and provide high-strength cement to support re-fracturing. After the critical point in non-clay fractures, porosity generation can outpace mineral precipitation and provide open pore space between re-fracturing events, a necessary prerequisite for permeability. After the critical point in clay-filled fractures, slip ceases to generate significant porosity from dilation during slip due to the “clogging” effect of the clay. Nevertheless, clay fractures widen and develop complexity over time due to alteration at the fracture core/damage zone boundary fed by fluids via microscopic porosity. Texas A&M/Temple University grant from the Department of Energy Geothermal Program This is an awesome thesis.