Thermal Geophysics

About this book

This book is intended as an introduction to thermal geophysics and contains material on the history of the subject, how to measure and correct heat flow, what heat flow and heat generation mean in the tectonic context, how geothermal energy is found and where the field of geothermics is going at present. The book will serve as a source of reference to the geothermal expert and is also intended for students and geologists.

Contents

1. Introduction and History . Components of geothermal research. Temperature and heat distribution within the earth. Terrestrial heat flow. Heat generation. Thermal properties of earth materials. Volcanology. Geothermal energy. Hydrocarbon formation. Fluid flow. Permafrost. Units. History of geothermal research. The collection of data. Speculations of thermal history. The advent of radioactivity. The first measurements of heat flow. 2. Measurement of Heat Flow on Land . Temperature measurement The use of thermistors. Calibration of thermistors. Thermistors in the field. Thermal conductivity. Heat-impulse methods. The divided bar. Heating probes for down-hole measurement. Conductivity of rock fragments. Conductivity of frozen rocks. Estimation of conductivity. The influence of porosity. Estimation of properties of frozen rocks. 3. Analysis and Correction of Heat Flow on Land . Calculation of heat flow. Selection of method of analysis. Correction of measurements. Correction for drilling disturbance. Correction for inclination of the borehole. Correction for climatic change. Correction for topographic relief. Correction for nearby bodies of water. Plane slopes. Lees hills. The sequence and value of corrections. Practical considerations. 4. Measurement of Heat Flow at Sea . The Bullard probe. The Ewing probe. Development of the sea-floor heat-flow probe. Thermal conductivity of the sea-floor sediments. Steady-state methods. The needle probe. Estimation by water content. Conductivity measurement in the ocean floor. Measurement from floating ice. Measurement in lakes and fjords. Measurement in deep-sea drill holes. 5. Disturbances and Corrections to Heat Flow in the Oceans. Sources of disturbance. Topographic disturbance. Accumulation of sediment. Sudden deposit of sediment. Water-temperature fluctuations. Measurement in lakes. The experimental lakes. 6. Thermal State of a Conductive Earth. The basic theory. The initial state. The meteorite theory. Melting point and adiabatic gradients. Thermal conductivity. Convection in the mantle. Radioactivity. Results of calculations. 7. Radioactivity and Heat Flow on the Continents. Measurement of radioactivity. Production of heat. Distribution of heat flow. Heat-flow provinces. The Sierra Nevada. Extension to non-plutonic rocks. Approximations. The Basin and Range province. The heat-flow province concept. Temperature in the crust. Frictional heating on faults. Active continental margins. Rifts and passive continental margins. 8. The Oceanic Crust. Observed heat-flow patterns. The concept of plate tectonics. The ocean ridges. Thermal models of spreading centres. Age of the ocean floor. Problems near the ridge crest. Heat flow over subduction zones. The marginal basins. Equality of continental and oceanic heat flow. 9. Geothermal Energy. Historical background. Definition of resources. Classification of resources. The properties of water. Vapour-dominated reservoirs. Fluid-dominated reservoirs.

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