Electrical Properties of Rocks

Recently there has been growing interest in the physical properties of rocks. To interpret data on the geophysical fields observed near the Earth's surface, we must know the physical properties of the materials composing the interior. Moreover, the development of geophysical methods (in particular, electrical methods) is necessitating a multiple approach to the study of the physical properties of rocks and minerals. In connection with problems now appearing, the physical properties of rocks must be studied in the laboratory under var­ ious thermodynamic conditions. Electrical methods of geophysi­ cal exploration often may require only data obtained at atmos­ pheric pressure and room temperature, or at temperatures below 100°C. If, however, we have in mind geophysical field observa­ tions on the composition and state of matter deep in the Earth's crust and mantle, we must conduct laboratory experiments at high pressures and temperatures. For example, in interpreting data from geomagnetic soundings of the mantle, we may need experi­ mental results on the electrical properties of rocks at pressures of tens of kilobars and temperatures of the order of lOOO°C. In this connection, we must remember that pressure has relatively little effect on the electrical properties of rocks, whereas, tem­ perature affects them very strongly. v vi FOREWORD At present, while research into the mechanical properties of rocks (relating to the problems of geophysics, geochemistry, geology, and mining) is pressing forward on a wide front, much less work is being done with electrical properties.

Contenu

Brief Review of the Petrography of Rocks.- Mineral Composition of Rocks.- Basic Rock Types.- Rock Structure.- Rock Texture.- Porosity and Water Content of Rocks.- Dielectric Properties of Rocks.- Dielectric Polarization.- Dielectric Permeability of Minerals.- Dielectric Constants of Rocks in Relation to Mineral Composition.- Effect of Moisture Content on the Dielectric Constant of Rocks.- Dielectric Constant of Anisotropic Rocks.- Effect of Pressure on the Dielectric Constant of Rocks.- Electrical Resistivity of Rocks.- Brief Review of the Electrical Conductivity of Dielectrics.- Electrical Conductivity of Semiconductors.- Methods of Determining the Resistivity of Rocks.- Electrical Resistivity of Minerals.- Effect of Mineral Composition on the Electrical Conductivity of Rocks.- Effect of Moisture Content on the Resistivity of Rocks.- Electrical Resistivity of Oil-Bearing Rocks.- Relationship Between Electrical Resistivity, Texture, and Anisotropy in Rocks.- Relationship Between Resistivity and the Other Physical Properties of Rocks.- The Effect of Temperature on the Resistivity of Rocks.- The Effect of Pressure on the Resistivity of Rocks.- Dielectric Loss in Rocks.- Brief Introduction to the Theory of Dielectric Loss.- Relationship of Dielectric Loss and Dielectric Constant to Frequency.- Relationship Between Dielectric Loss, Dielectric Constant, and Temperature.- Equipment and Methods for Determining Dielectric Constant and Dielectric Loss.- The Effect of Frequency and Temperature on Dielectric Loss and Dielectric Constant in Minerals.- Relationship of Dielectric Constant, Dielectric Loss and Resistivity of Rocks to Frequency.- Relationship of Dielectric Constant and Dielectric Loss in Rocks to Temperature.- Conclusions.- References.- Supplementary Guide to the Literature on Electrical Properties of Rocks and Minerals.- Basic Principles.- Electrical Properties of Rocks Containing Conductive Minerals.- Electrical Properties of Water-Bearing Rocks.- Electrical Properties of Dry Rocks.- Dielectric Constants, Dielectric Loss, and Induced Polarization.- Average Electrical Properties of Large Masses of Rock.