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2021 | Book

Thermal Structure of the Earth Read chapter Read first chapter

Geothermal Energy

From Theoretical Models to Exploration and Development

Authors: Prof. Dr. Ingrid Stober, Dr. Kurt Bucher

Publisher: Springer International Publishing

Part of: Springer Professional "Wirtschaft+Technik" , Springer Professional "Technik"

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About this book

The internal heat of the planet Earth represents an inexhaustible reservoir of thermal energy known as Geothermal Energy. The 2nd edition of the book covers the geologic and technical aspects of developing all forms of currently available systems using this "renewable" green energy. The book presents the distribution and transport of thermal energy in the Earth. Geothermal Energy is a base load energy available at all times independent of climate and weather. The text treats the efficiency of diverse shallow near surface installations and deep geothermal systems including hydrothermal and petrothermal techniques and power plants in volcanic high-enthalpy fields. The book also discusses environmental aspects of utilizing different forms of geothermal energy, including induced seismicity, noise pollution and gas release to the atmosphere. Chapters on hydraulic well tests, chemistry of deep hot water, scale formation and corrosion, development of geothermal probes, well drilling techniques and geophysical exploration complete the text. This book, for the first time, covers the full range of utilization of Geothermal Energy.

Table of Contents

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. An example: The “renewable” aspect of burning firewood in a cooking stove lies in the relatively short period of time required to regrow chopped down forests with solar energy and the process of photosynthesis. In contrast, it will take much more time to “renew” coal beds when burning coal for the same purpose, although geological processes will eventually form new coal beds. The “renewable” aspect of geothermal energy will be explained and discussed in detail in this chapter and Chap. 3.
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.
Using thermal water for energy conversion did not start before the second half of the 19th century related to the rapid development of thermodynamics. Thermodynamics helped to efficiently convert energy from hot steam first in mechanical energy and then into electrical energy with the help of turbines and generators.
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.
The different forms of energy can be converted from one to another. E.g., chemical energy is converted to mechanical energy in a combustion engine. Solar heat radiation is converted in a photovoltaic system into electrical current.
The distinction between renewable and non-renewable forms of energy resulted from the increasing insight that natural energy resources are limited. Non-renewable kinds of energy, also called fossil energy resources, include coal, oil, gas and nuclear fuels (e.g. uranium). These forms of energy renew on time scales that are not interesting for the present day human economic system.
Ingrid Stober, Kurt Bucher
Chapter 4. Uses 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. Deep geothermal systems exploit geothermal energy by means of deep boreholes. The mined thermal energy can be used directly and does not require further transformation. Near surface geothermal systems, extract thermal energy from the uppermost layer of the earth crust. Typical systems include: ground heat collectors, borehole heat exchangers, boreholes into groundwater, and geothermal energy piles. The exploitation is indirect and requires conversion with e.g. heat pumps. Utilization of geothermal energy from high-enthalpy reservoirs, typical of active volcanic regions is treated in Chap. 10 separately.
Ingrid Stober, Kurt Bucher
Chapter 5. Potential and 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. 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
Geothermal probes are liquid-filled tubes installed in a borehole. There are different types of geothermal probes including single U-tube probes, double U-tube probes and coaxial probes. Cool liquid flows downward in the tubes and accumulates heat from the surrounding ground. The warmed liquid turns around in the U-shaped foot at bottom hole and flows back to the heat pump at the surface. The heat pump uses the extracted ground heat to increase the fluid temperature of a secondary cycle so that it can be used for heating purposes. To promote sustainability and long term operation of the heating system it is important to limit the withdrawal of thermal energy from the ground during the annual house heating period to the natural heat influx to the reservoir. Heat extraction must be balanced by natural regeneration.
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. They can be used for both heating and cooling. Geothermal well systems are a form of direct-use systems of near surface groundwater. The use of geothermal energy from groundwater can be particularly energy efficient. The direct-use of groundwater as a heat transfer fluid minimizes energy losses in heat exchanger systems. The relatively constant temperature of the groundwater flow is ideal for heat extraction by heat pumps. The advective heat transfer by groundwater flow has clear advantages regarding efficiency and economy compared with the conductive heat transfer utilized in geothermal probes.
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. 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. Profitable electrical power production is possible at fluid temperatures above 120 °C. The thermal water is produced from deep groundwater reservoirs (aquifers). In principle, thermal water may also be retrieved from water conducting faults and fault zones, however, hydrothermal systems typically connect to aquifers.
Ingrid Stober, Kurt Bucher
Chapter 9. Enhanced-Geothermal-Systems (EGS), Hot-Dry-Rock Systems (HDR), Deep-Heat-Mining (DHM)
Abstract
Enhanced-Geothermal-Systems (EGS) use the deep underground as a source of heat for the production of electrical and thermal energy irrespective of the hydraulic properties of the deep heat reservoir. The upper continental crust is always fractured; its fracture density differs however. A saline, occasionally gas-rich fluid is typically present on 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, EGS systems strongly focus on granitic heat reservoirs. Typical target temperatures for EGS systems are above 200 °C. This means that wellbores of 6 to 10 km have to be drilled in continental crust with an average geothermal gradient.
Ingrid Stober, Kurt Bucher
Chapter 10. Geothermal Systems in High-Enthalpy Regions
Abstract
Most of the electrical power produced from geothermal resources worldwide originates from regions with extreme geothermal gradients and very high surface heat-flow. The regions attain high ground temperatures at shallow depth and are typically found in active volcanic areas, young rift systems and similar geological settings. These geothermal sources are also known as high-enthalpy reservoirs or high-enthalpy systems with reference to the high heat content of the reservoir fluid used as heat transfer medium. High-enthalpy systems produce electrical power directly from dry steam or from a high-temperature two-phase fluid in flash-steam plants.
Ingrid Stober, Kurt Bucher
Chapter 11. Environmental Issues Related to Deep Geothermal Systems
Abstra
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.
Construction of geothermal systems and power plants causes CO2 emissions related to manufacturing construction materials, transport of materials and equipment and service traffic, no different as with construction of other types of power plants. Careful planning of logistics helps to minimize these emissions.
Developing the underground heat exchanger of an enhanced geothermal system involves hydraulic stimulation measures that cause minor seismicity. Rarely the induced seismicity can cause irritation if physically sensed at the surface.
Ingrid Stober, Kurt Bucher
Chapter 12. 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 are higher by a factor of 2–5 compared to boreholes in the oil and gas industry.
Ingrid Stober, Kurt Bucher
Chapter 13. 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. In Chap. 13, we briefly present a selection of geophysical investigation methods.
Ingrid Stober, Kurt Bucher
Chapter 14. 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 in the intended target horizon. Chapter 14 gives a brief overview over some standard hydraulic testing methods, the practical conductance of the tests and the processing and interpretation of measured data.
Hydraulic tests may solve very diverse problems. Therefore, the appropriate testing procedures depend on the specific data needed to answer the current question. However, all test methods monitor water pressure changes that result from an incurred excursion from the undisturbed pressure distribution in the reservoir. The excursion is being imposed by the testing method. A large variety of hydraulic testing schemes are currently used in groundwater exploration, by the oil and gas industry and in geothermal energy plant development
Ingrid Stober, Kurt Bucher
Chapter 15. The Chemical Composition of Deep Geothermal Waters and Its Consequences for Planning and Operating a Geothermal Power Plant
Abstract
The fracture porosity of continental crust is normally saturated with an aqueous fluid. This fluid is used for transferring 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 molal NaCl equivalents corresponding to a total of dissolved solids (TDS) in the range of 60 to 270 g L−1. The chemical composition of the fluid has a number of consequences for geothermal exploration and also for the later operation of a power plant that will be briefly explored in this Chap. 15.
Ingrid Stober, Kurt Bucher
Metadata
Title
Geothermal Energy
Authors
Prof. Dr. Ingrid Stober
Dr. Kurt Bucher
Copyright Year
2021
Electronic ISBN
978-3-030-71685-1
Print ISBN
978-3-030-71684-4
DOI
https://doi.org/10.1007/978-3-030-71685-1