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2013 | Buch

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Geothermal Energy

From Theoretical Models to Exploration and Development

verfasst von: Ingrid Stober, Kurt Bucher

Verlag: Springer Berlin Heidelberg

Enthalten in: Springer Professional "Wirtschaft+Technik" , Springer Professional "Technik"

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Über dieses Buch

The internal heat of the planet Earth represents an inexhaustible reservoir of thermal energy. This form of energy, known as geothermal energy has been utilized throughout human history in the form of hot water from hot springs. Modern utilization of geothermal energy includes direct use of the heat and its conversion to other forms of energy, mainly electricity. Geothermal energy is a form of renewable energy and its use is associated with very little or no CO2-emissions and its importance as an energy source has greatly increased as the effects of climate change become more prominent. Because of its inexhaustibility it is obvious that utilization of geothermal energy will become a cornerstone of future energy supplies. The exploration of geothermal resources has become an important topic of study as geology and earth science students prepare to meet the demands of a rapidly growing industry, which involves an increasing number professionals and public institutions participating in geothermal energy related projects. This book meets the demands of both groups of readers, students and professionals. Geothermal Energy and its utilization is systematically presented and contains the necessary technical information needed for developing and understanding geothermal energy projects. It presents basic knowledge on the Earth’s thermal regime and its geothermal energy resources, the types of geothermal energy used as well as its future potential and the perspectives of the industry. Specific chapters of the book deal with borehole heat exchangers and with the direct use of groundwater and thermal water in hydrogeothermal systems. A central topic are Enhanced Geothermal Systems (hot-dry-rock systems), a key technology for energy supply in the near future. Pre-drilling site investigations, drilling technology, well logging and hydraulic test programs are important subjects related to the exploration phase of developing Geothermal Energy sites. The chemical composition of the natural waters used as a heat transport medium in geothermal systems can be used as an exploration tool, but chemistry is also important during operation of a geothermal power plant because of potential scale formation and corrosion of pipes and installations, which needs to be prevented. Graduate students and professionals will find in depth information on Geothermal Energy, its exploration and utilization.

Inhaltsverzeichnis

Frontmatter

Chapter 1. Thermal Structure of the Earth

Abstract

The term “renewable energy” is used for a source of energy from a reservoir that can be restored on a “short time scale” (in human time scales). Renewable energy includes geothermal energy and several forms of solar energy such as bio-energy (bio-fuel), hydroelectric, wind-energy, photovoltaic and solar-thermal energy. These sources of energy are converted to heat or electricity for utilization.

Ingrid Stober, Kurt Bucher

Chapter 2. History of Geothermal Energy Use

Abstract

Geothermal energy, heat from the interior of the planet Earth, has been utilized by mankind since its existence. Hot springs and hot pools have been used for bathing and health treatment, but also for cooking or heating. The resource has also been used for producing salts from hot brines. For the early man the Earth internal heat and hot springs had religious and mythical connotation meaning. They were the places of the Gods, represented Gods or were endowed with divine powers. In many modern societies bathing in hot spring spas has still preserved the meaning of a divine ceremony.

Ingrid Stober, Kurt Bucher

Chapter 3. Geothermal Energy Resources

Abstract

In physics, energy is the ability of a physical system to do work on other physical systems. There are many different forms of energy including mechanical (potential, kinetic), thermal, electric, chemical and nuclear energy. Thermal energy can be understood as the random motion of atoms and molecules.

Ingrid Stober, Kurt Bucher

Chapter 4. Applications of Geothermal Energy

Abstract

The distinction between near surface and deep geothermal systems follows from the different depth levels of the geothermal reservoirs and different techniques of utilization (Fig. 4.1). Yet, the transition between the two worlds is smooth. Distinguishing the two main fields of geothermal energy utilization is useful, because their specific techniques for energy production require different geological and geophysical parameters for the description of the systems.

Ingrid Stober, Kurt Bucher

Chapter 5. Potential Perspectives of Geothermal Energy Utilization

Abstract

Geothermal energy is renewable energy in the sense that heat extraction by technical systems is replenished by heat flow from the heat reservoir of the Earth. The latter is virtually inexhaustible at human time scales (Sect. 1.3). Although the ultimate heat reservoir is in effect everlasting, the question of sustainability of geothermal energy utilization must be answered for each individual site, plant and location separately because it depends on the system design and the dimensioning of the installation.

Ingrid Stober, Kurt Bucher

Chapter 6. Geothermal Probes

Abstract

The basic condition of near-surface geothermal energy utilization is the low temperature of the thermal reservoir. The temperature is typically lower than the working temperature of house heating. The heat transfer fluid in house heating systems requires a minimum temperature of about 20–30 °C, whereas ground temperatures are typically in the range of 5–15 °C. Therefore, in order to use the geothermal energy for the heating of buildings the transfer fluid temperature must be increased by means of a heat pump system. The highest reservoir temperatures are accessible to geothermal probes. Depending on the depth of the probe, drillhole heat exchangers may provide fluid temperatures of 10–12 °C depending on the local conditions (Central Europe). The temperature increase needed by the house heating system is then done by the heat pump. Most heat pumps are driven electrically. Electricity is expensive and produced with large losses from fossil energy resources in some countries.

Ingrid Stober, Kurt Bucher

Chapter 7. Geothermal Well Systems

Abstract

Geothermal well systems utilize the thermal energy of clean groundwater of hydraulically highly conductive aquifers with water tables close to the surface. The thermal energy of water produced from the well can be extracted by means of heat pumps. Such systems are also called two-well-systems, water–water-heat-pump-systems, or groundwater heat pump. Geothermal well systems are a form of direct-use systems of near surface groundwater.

Ingrid Stober, Kurt Bucher

Chapter 8. Hydrothermal Systems, Geothermal Doublets

Abstract

Hydrothermal systems use the thermal energy of an aqueous fluid at greater depths. Depending on the heat content of the fluid, systems with high enthalpy can be distinguished from low enthalpy systems. High enthalpy systems produce electrical power directly from hot steam or from a high-temperature two-phase fluid (Sect. 4.2). Low-enthalpy systems use the warm or hot water directly or via a heat exchanger to feed local or district heating systems, for industrial or agricultural utilization or for balneological purposes.

Ingrid Stober, Kurt Bucher

Chapter 9. Enhanced-Geothermal-Systems, Hot-Dry-Rock Systems, Deep-Heat-Mining

Abstract

With Enhanced-Geothermal-Systems (EGS) the deep underground is used as a source of heat for the production of electrical and thermal energy irrespective of the hydraulic properties of the deep heat reservoir. In other words the rocks are hot at depth irrespective of whether or not they qualify as aquifers or aquitards. Weakly fractured granites at depth are best described as “hot dry rocks” (HDR systems). However, keep in mind that also the few fractures present are interconnected and filled with hot pore water. The term “hot dry rock” originates from the early-days of geothermal energy utilization where the concept was to drill a deep wellbore into hot but assumingly dry rocks for extraction of thermal energy. Later it was found that the fracture porosity of continental rocks is always saturated with hot water so that the term hot-dry-rock became rather misleading. The upper continental crust is always fractured; its fracture density differs however. A saline, occasionally gas-rich fluid is typically present in the fractures. The geothermal utilization of the hot underground with low hydraulic conductivity is sometimes also referred to as “deep heat mining” (DHM). Because the continental crust is predominantly granitic or gneissic, HDR systems strongly focus on granitoid heat reservoirs. Typical target temperatures for HDR systems are above 200 °C. This means that wellbores of 6–10 km have to be drilled in continental crust of average geothermal gradient.

Ingrid Stober, Kurt Bucher

Chapter 10. Environmental Issues Related to Deep Geothermal Systems

Abstract

The conversion of geothermal energy into electrical power or useful heat produces no CO₂ and no flue gas emissions such as soot particles, sulfur dioxide and nitrogen oxides. The operation of a geothermal power plant is deeply friendly to the environment. The risk for harmful environmental effects is extremely low during normal operation and even during accidents. The low-risk systems result from the use of high-quality structural materials and from the mature technology with numerous safety precaution installations.

Ingrid Stober, Kurt Bucher

Chapter 11. Drilling Techniques for Deep Wellbores

Abstract

Drilling costs stand for about 70 % of the total costs of a deep geothermal project. The drilling technique used in deep geothermal projects has been adopted for the most part from the oil and gas industry. The drilling technique used in geothermal projects, however, must satisfy higher requirements because of the combination of high temperatures, high volume fluxes and typically high concentrations of aggressive and corrosive solutes in the produced fluid. Borehole diameters are larger because of the high volume fluxes. In contrast to oil and gas wells, wellbores in the geothermal industry must provide evidence for an operation life of 30 years. Geothermal wells pump hot salty fluids directly along the casing to the surface. In contrast, oil wells produce hydrocarbons along a liner protecting the casing. The costs for a deep drillhole in the geothermal industry is higher by a factor of 2–5 compared to boreholes in the oil and gas industry

Ingrid Stober, Kurt Bucher

Chapter 12. Geophysical Methods, Exploration and Analysis

Abstract

Geophysical sounding and investigations provide an indirect view into the underground. Geophysical investigations collect data using instruments at the surface or placed in boreholes. Borehole geophysics and geophysical well logging can probe and research in cased and in uncased bores.

Ingrid Stober, Kurt Bucher

Chapter 13. Testing the Hydraulic Properties of the Drilled Formations

Abstract

Hydraulic tests provide the key data on the hydraulic conductivity of the reservoir formation and permeability structure of the reservoir. These hydraulic properties are fundamental for the success of a geothermal project. The first hydraulic tests are already made in the hanging wall of the intended reservoir formation during drilling of the deep well. After completion of the wellbore, the hydraulic properties of the reservoir formation must be extensively tested. This includes long-term tests, circulation experiments, or tracer tests. Chapter 13 gives a brief overview over some standard hydraulic testing methods, the practical conductance of the tests and the processing and interpretation of measured data.

Ingrid Stober, Kurt Bucher

Chapter 14. The Chemical Composition of Deep Geothermal Waters and Its Consequences for Planning and Operating a Geothermal Power Plant

Abstract

The fracture porosity of the continental crust is normally saturated with an aqueous fluid. This fluid is used to transfer thermal energy from the hot depth to the cold surface for various uses. The chemical composition of this natural heat transfer fluid depends on the predominant (reactive) rock type of the thermal reservoir and its changes along the circulation pathway. Most deep fluids are saline brines with the major components NaCl and CaCl₂. Typical deep fluids contain between 1 and 4 molar NaCl equivalents corresponding to a total of dissolved solids (TDS) in the range of 60–270 g/L.

Ingrid Stober, Kurt Bucher

Backmatter

Titel: Geothermal Energy
verfasst von: Ingrid Stober
Kurt Bucher
Verlag: Springer Berlin Heidelberg
Electronic ISBN: 978-3-642-13352-7
Print ISBN: 978-3-642-13351-0
DOI: https://doi.org/10.1007/978-3-642-13352-7