Earth and Planetary Sciences ETDs

Publication Date

3-3-1978

Abstract

Permeability of quartz monzonite from the Los Alamos hot-dry-­rock geothermal well GT-2 was experimentally measured as a function of pressure and temperature. Permeability apparatus slightly modified from that developed by Brace and others (1968) was used in the experiments. Flow rate through the sample was measured using a transient pressure decay method. When combined with the physical characteristics of the sample and several system parameters, this flow rate yielded permeability (k). Permeability of the GT-2 rocks from depths of 8580 ft and 9522 ft behaves like Westerly granite for changes in effective confining pressure. However permeability of these rocks behaves much differently with increasing temperature. As temperature is increased, the permeability of Westerly granite passes through a slight minimum and then increases exponentially above 100°c. Upon cooling the permeability shows a permanent increase of up to four times its original value. The permeability of GT-2-9522', on the other hand, drops off exponentially with increasing temperature, reaching a minimum near 140°c; above 150 permeability rises slowly. The GT-2-8580' sample shows somewhat similar behavior, although the permeability shows a minimum near 130°C, followed by a rather sharp rise in permeability at higher temperature. These changes in permeability with temperature are postulated to be caused by differential thermal expansion (DTE), a phenomena related to the anisotropic and inhomogeneous coefficients of thermal expansion of the mineral grains in the rock. Scanning electron photomicrographs of unheated and heated samples of Westerly and GT-2 rocks support the DTE hypothesis. Differences in the behavior of these rocks with temperature are believed to be due to the respective temperature and pressure environments in which they became equilibrated, since both GT-2 rocks had existed at moderately high temperatures and pressures for some time. Temperature disequilibrium of the GT-2 rocks in their present in situ environments is believed to have caused the differences in the behavior between the two samples. This disequilibrium may provide a method for determining the pre-intrusion geothermal gradient of the Jemez area. Flow channels were observed in GT-2 samples using radioactive racer techniques. Several radioactive isotopes were tried in these experiments, including 22Na, 63Ni, and 35S. Cores were injected with the radioisotope using the permeability apparatus; they were then thick-sectioned and autoradiographed. 63Ni provided the best spatial resolution, since it emits the lowest energy electron. These channel-tracing efforts indicated that at low pressures, fluid transport through the rock is most commonly along intergranular channels. Intragranular channels were not observed with this technique.

Degree Name

Earth and Planetary Sciences

Level of Degree

Masters

Department Name

Department of Earth and Planetary Sciences

First Committee Member (Chair)

Jonathan Ferris Callender

Second Committee Member

Douglas Gridley Brookins

Third Committee Member

John P. Balagna

Fourth Committee Member

Gary Perrin Landis

Project Sponsors

This work was supported by many friends. We welcome this opportunity to thank them for their help. We would particularly like to thank Dr. Jonathan F. Callender, of the Department of Geology UNM and Dr. Rosemary J. Vidale of Los Alamos Scientific Laboratory; without their help and encouragement this work would not have been possible. We would also like to thank several other members of the UNM Geology Department, Dr. Douglas G. Brookins and Dr. Gary P Landis, for reading the manuscript and adding helpful comments. Special thanks to Jack Fullbright of the M-1 group at LASL for many ideas and help with the radiotracer technique. Dr. Raymond C. Fletcher of Stanford University was the first to suggest the idea that permeability minimums might coincide with specific temperature and pressure conditions. Dr. Robert W. Charles was instrumental in the design and operation of the permeability equipment, he added many valuable ideas and without his help things would not have gone as smoothly. He also was of great help in the scanning electron microscopy part of this work. We would also like to thank the members of Group G-3 at Los Alamos for many helpful discussions. Much help in the design and construction of the equipment must be credited to the men in the machine shop in Group CNC-11, Los Alamos Scientific Laboratory. Many thanks to Marsha Potter for helping with some of the typing. Financial support for this work was provided by the Los Alamos Scientific Laboratory through funds derived from the hot-dry rock geothermal program.

Language

English

Document Type

Thesis

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