Geothermics

The constantly growing demand for energy, as well as the realization during the past decade that fossil energy reserves to satisfy ever­ increasing energy consumption are limited, have helped, as part of the search for alternative energy sources, to bring the subject of geothermics to its present level of significance. Practical geothermics is concerned with prospecting for and develop­ ment of geothermal heat. General geothermics deals with the thermal state of our Earth as a whole. Both divisions of this field, however, contribute practical insights, and improved methods of temperature esti­ mation have helped to give us a better picture of detailed thermal condi­ tions. It is difficult for readers interested in this field to obtain an overview from the numerous, specialized papers that have been written on geother­ mics. This book is meant to provide a thorough introduction to the subject, although the coverage is not exhaustive is detail. Geothermics is taught at universities and technical institutes, as part of the curriculum in geology. This introduction to geothermics is directed especially to students of geophysics and is meant to be used as a supple­ ment to their lectures. of this work must be given to my Special thanks for the completion teacher, Prof. Dr. O. ROSENBACH. His lectures in geophysics inspired my interest in geothermics, which is still my main research area.

Contenu

1 Physical Basis of Heat Transfer.- 1.1 Temperature and Temperature Gradient.- 1.2 Heat Flow Density, Thermal Conductivity and Thermal Diffusivity.- 1.3 The Heat Conduction Equations.- 2 Thermal Properties of Common Rocks.- 2.1 Thermal Conductivity.- 2.1.1 Temperature Influence on Thermal Conductivity.- 2.1.2 Pressure Influence on Thermal Conductivity.- 2.1.3 Thermal Conductivity of Anisotropic Bodies.- 2.1.4 Thermal Conductivity of Porous Rocks.- 2.2 Specific Heat.- 2.3 Radiogenic Heat Production.- 2.3.1 Radioactivity of Rocks on the Earth's Surface.- 2.3.2 Methods for Estimating Radioactive Heat Production in the Earth's Interior.- 3 Analytical Treatment of Conductive Cooling in the Crust.- 3.1 Thermal Equilibration in the Homogenous Half Space.- 3.1.1 Half Space with a Boundary Surface.- 3.1.2 Subsurface with a Cover of Lava.- 3.2 Temperature Equilibration in Model Bodies.- 3.2.1 Cooling of Igneous Dikes.- 3.2.2 Cooling of Spherical Intrusions.- 3.2.3 Cooling of Rectangular Intrusions.- 4 Thermal State of the Earth's Interior.- 4.1 Thermal State of the Upper Crust.- 4.1.1 Influence of Climatic Variations on the Surface Temperature.- 4.1.1.1 Diurnal and Annual Variations of the Surface Temperature.- 4.1.1.2 Long-Term Temperature Variations.- 4.1.2 Topographic Influence on the Subsurface Temperature Field.- 4.1.3 Changes in the Temperature Field Caused by Water Movement.- 4.1.4 Temperature Fields in Different Types of Geological Structures.- 4.1.5 Terrestrial Heat Flow Density.- 4.1.5.1 Regional Variation of Heat Flow Density.- 4.1.5.2 Secular Variation of Heat Flow Density.- 4.2 Thermal State in the Lower Crust and Deeper Interior.- 4.2.1 Thermal State of the Lower Crust and Upper Mantle.- 4.2.2 Thermal State of the Lower Mantle.- 4.2.3 Thermal State of the Core.- 4.3 Thermal Aspects of Plate Tectonics.- 5 Methods for Determining Temperature.- 5.1 Geothermometers for Evaluating Reaction Temperatures.- 5.1.1 Solution Equilibria as Temperature Indicators.- 5.1.1.1 The SiO2-Thermometer.- 5.1.1.2 The Na-K-Ca-Thermometer.- 5.1.2 Isotope Ratios as a Geothermometer.- 5.1.3 Trace Elements in Salts and Ores.- 5.1.4 The Garnet-Pyroxene Thermometer.- 5.1.5 The Dolomite-Calcite Thermometer.- 5.1.6 The Degree of Coalification of Organic Inclusions in Sedimentary Rocks.- 5.2 Geophysical Methods for Determining Temperatures.- 5.2.1 Direct Measurements at the Earth's Surface and in Borehole.- 5.2.2 Indirect Methods for Determining Temperatures.- 5.2.2.1 Temperature Determination from Gravimetric Measurements.- 5.2.2.2 Temperature Determination from Geoelectric Measurements.- 5.2.2.3 Results from Magnetotellurics as Temperature Indicators.- 5.2.2.4 Shape of the Curie-Point as an Isotherm.- 5.2.2.5 Temperature Estimates from Seismic Results.- 6 Geothermal Heat as an Energy Source.- 6.1 Prospecting Methods for Thermal Reservoirs.- 6.1.1 Geochemical and Geological Methods.- 6.1.1.1 Mapping Hydrothermal Alteration.- 6.1.1.2 Investigations of Thermal Water.- 6.1.1.3 Trace Elements in the Soil.- 6.1.1.4 Alteration of Coaly Materials in Sedimentary Rock.- 6.1.2 Geophysical Methods.- 6.1.2.1 Infrared Measurements.- 6.1.2.2 Shallow Temperature Measurements and Heat Flow Density.- 6.1.2.3 Gravimetric Measurements.- 6.1.2.4 Geoelectric Measurements.- 6.1.2.5 Seismic Methods.- 6.2 Utilization of Geothermal Energy.- 6.2.1 Use of Thermal Water in Swimming Pools.- 6.2.2 Thermal Water of Space Heating.- 6.2.3 Converting Geothermal Energy to Electrical Energy.- 6.2.3.1 Exploitation of Steam.- 6.2.3.2 Hot Dry Rock as an Energy Source.- 6.2.3.3 Exploitation of Hot Water.- 6.2.4 Environmental Impact of Geothermal Exploitation.- 7 Appendix.- 7.1 Error Function.- 7.2 Answer to the Problems.- 8 References.- 9 Subject Index.