The growth in renewable electricity generation is forecast to continue as fossil fuel levels decrease and carbon dioxide emissions are penalized. The growth in geothermal is becoming constrained as conventional high-temperature sources are fully exploited. Geothermal can be a cost competitive base load power source. Governments and utilities are looking at the potential of electricity generation from low temperature geothermal resources for future development. This technology, unlike the high and medium temperature, is not mature and there are a number of companies looking at entering the Organic Rankine Cycle (ORC) market. This thesis aims to provide a necessary step for reliable commercial develop this technology by developing the first draft of a low temperature geothermal ORC standard. The standard outlines the critical stages of a geothermal ORC project as the Prospecting stage; Pre-Feasibility stage, Feasibility stage, and the Detailed Design stage. The standard is unlike other standards that are used to design one component; this standard guides the engineers though the various critical steps of the ORC design to correctly assess the geothermal resource and to inform design and investment decisions. The standard provides particular guidance on critical factors in ORC design, primarily the working fluid selection and component selection limitations. Experienced industry engineers have provided advice and insight regarding the critical design points and processes. The draft standard was reviewed by a number of geothermal industry engineers who have worked with large scale, conventional ORCs. They each commented on the standard from their prospective in the industry and gave general feedback was that it is a technically relevant standard that can be used as a potential start point to develop a new standard for the low temperature binary ORC industry. The final draft standard has been submitted to the ISO for consideration. This thesis first sets out the general background on the state of the art and the industry for lowtemperature binary ORC power plants, and provides the review assessment of the standard draft. However, the bulk of the thesis is the standard itself. The standard represents a substantial contribution to the mechanical and thermal systems engineering field.

This thesis considers economic factors for reducing greenhouse gas emissions from utility-scale electricity generation in California. The statewide Emission Performance Standard and Renewables Portfolio Standard have led to the announced and projected retirement of many coal power facilities serving California electricity load. This reality requires new baseload power sources to meet growing energy demands over the next several decades. The economic and environmental feasibilities of competitive baseload generation technologies are assessed to determine suitable replacements for decommissioning coal power plants. Geothermal is identified as the optimal replacement due to its economic baseload functionality, low greenhouse gas emissions, small environmental impact, and resource abundance in many regions of California. Developing geothermal capacity from the Salton Sea could provide southern California with a reliable energy source for decades while simultaneously reducing adverse environmental impacts and greenhouse gas emissions from electricity generation in California.

The Ngatamariki Geothermal Field is located 20 km north of Taupo in the Taupo Volcanic Zone and has a boundary of 12 km² as delineated by magneto-telluric surveys (Urzua 2008). Rhyolitic deposits, derived from the Maroa Volcanic Centre, dominate the geology of the area with the 186 AD (Wilson et al. 2009) Taupo pumice mantling stream valleys in the area. The majority of thermal features at Ngatamariki are located along the Orakonui Stream on the western boundary of the field; the stream area is dominated by a 50x30 m geothermal pool filling a hydrothermal eruption crater. This crater was formed during a hydrothermal eruption in 1948, with a subsequent eruption in April 2005. Orakei Korako is located 7 km north of Ngatamariki and has one of the largest collections of thermal features in New Zealand. The geology at Orakei Korako is similar to Ngatamariki, but the area is dominated by a series of south-west trending normal faults which create sinter terraces on the eastern bank of Lake Ohakuri. Water samples from springs and wells at Ngatamariki and Orakei Korako were taken to assess the nature of both fields. Spring waters at Ngatamariki have chloride contents of 56 to 647 mg/l with deep waters from wells ranging from 1183 to 1574 mg/l. This variation is caused by mixing of deep waters with a steam heated groundwater, above clay caps within the reservoir. Stable isotopic results (δ¹⁸O and δD) suggest that reservoir waters are meteoric waters mixed with magmatic (andesitic) water at Ngatamariki. Reservoir water chemistry at Orakei Korako exhibits low chloride contents, which is anomalous in the Taupo Volcanic Zone. Chloride content in well and spring waters is similar ranging from 546 to 147 mg/l, due to mixing of reservoir fluids with a ‘hot water’ diluent at depth. Isotopic compositions of spring waters suggest that they are meteoric waters which mix with magmatic (rhyolitic) water, more enriched in δ¹⁸O and δD than ‘andesitic’ water. Relationships between major ion concentrations and known subsurface geology suggest there is no hydraulic connection between the two fields.

There are many sources of free energy available in the form of heat that is often simply wasted for want of an effective way to convert it into useful energy such as electricity. The aim of this research project is to design and build a low temperature differential Stirling engine capable of generating electric power from heat sources such as waste hot water or geothermal springs. The engine that has been developed is a research prototype model of a new type of design featuring a rotating displacer which is actuated by a pair of stepper motors. The rotating displacer design enables the use of readily available and comparatively cheap and robust steam pipe as the housing for the engine, and it also avoids problems associated with sealing and heat exchange that would be present in a large engine of a more traditional configuration. Owing to the fact that this engine is a research prototype, it has the ability to have some of its critical operating parameters such as phase angle and stroke length adjusted to investigate the effects on performance. When the next phase of development takes place most of these parameters will be fixed at the optimum values which will make manufacture cheaper and easier. Unfortunately, construction of the prototype engine has not been completed at the time of writing so no power producing results have been achieved; however thorough results are presented on the operation of the control system for the stepper motors which actuate the displacer. Additionally, after a thorough history and background of Stirling engines was researched, the understanding gained of how these engines work has enabled a design process to take place which has hopefully led to a successful design. Analysis of various aspects of the engine have been carried out and results look promising for the engine to produce around 500 Watts of electrical power output whilst running on hot water up to around 90°C.

Deep drilling is required to reach the geothermal fluids extracted for generation of electricity; therefore, the different rock properties and the hydrothermal alteration of the lithologies being drilled become an important factor to a conventional geothermal industry. If the correct equipment required to complete drilling is not selected, the rate of penetration (ROP) can be suboptimal, potentially increasing the cost of the project. Mechanical characterisation of hydrothermally altered rocks from geothermal reservoirs will lead to an improved understanding of rock mechanics in a geothermal environment. Core samples obtained from the Ngatamariki, Rotokawa and Kawerau Geothermal Fields covered a wide range of lithologies (ignimbrite, rhyolite lava, sandstone, mudstone, andesite lava/breccia and tonalite) encountered during drilling. A suite of non-destructive and destructive laboratory tests along with petrographical analysis were conducted on the samples. Some key findings are that samples that originated from the shallow and low temperature section of the Kawerau geothermal field had higher porosity (15 – 56%), lower density (1222 – 2114 kg/m3) and slower ultrasonic wave velocities (1925 – 3512 m/s (vp) and 818 – 1980 m/s (vs)), than the samples from a deeper and higher temperature section of the field (1.5 – 20%, 2072 – 2837 kg/m3, 2639 – 4593 m/s (vp) and 1476 – 2752 m/s (vs), respectively). The shallow lithologies had uniaxial compressive strengths (UCS) of 2 – 75 MPa, and the deep lithologies had strengths of 23 – 211 MPa. Typically samples of the same lithologies that originate from multiple wells across a field have variable rock properties because of the different alteration zones from which each sample originates. To obtain a way to relate this rock property data back to the geomechanical model, we developed a method - Alteration Strength Index (ASI) - to address the effect of hydrothermal alteration on mechanical rock properties. The index constitutes three components; the mineralogy parameter, derived from petrological analysis, alteration index (degree of alteration) and an assessment of mineral hardness; the fracture parameter, assigned based on an assessment of structural damage; and the porosity parameter, which accounts for the effect of voids. This method can be used to estimate a range of rock strengths comparable to UCS, and the ASI calibrated against measured UCS for the samples produced a strong correlation (R2 of 0.86). From this correlation an equation was derived to convert ASI to UCS. Because the ASI–UCS relationship is based on an empirical fit, the UCS value that is obtained from conversion of the ASI includes an error of 7 MPa for the 50th percentile and 25 MPa for the 90th percentile with a mean error of 11 MPa. A sensitivity analysis showed that the mineralogy parameter is the dominant characteristic in this equation, and the ASI equation using only mineralogy can be used to provide an estimated UCS range, although the uncertainty becomes greater. This provides the ability to estimate strength even when either fracture or porosity information are not available, for example in the case of logging drill cuttings. To determine the usefulness of the ASI method with drill cuttings and drilling data we compared it to two methods; mechanical specific energy (MSE) and R/N-W/D chart, both developed for the oil and gas industry, in a geothermal context. We demonstrated how they can be used to estimate a range of rock strengths for hydrothermally altered lithologies for the 800 metre long 17 inch (432 mm) diameter section of well NM8 in the Ngatamariki Geothermal Field, New Zealand. We found that MSE and the R/N-W/D charts correctly ranked relative strength to ROP for three of six lithologies, while ASI correctly ranked all six lithologies. We also show that the strength values predicted by ASI correlate to ROP better than those based on MSE or R/N-W/D. We argue that ASI is more comprehensive than these methods because it provides a range of rock strength indices for a given hydrothermally altered lithology, is based on the geology, and does not require drilling parameters (ROP, WOB, RPM, and Torque) to estimate rock strength. This is particularly important in geothermal systems where lithologies can exhibit high variability in their physical characteristics and geothermal fields tend to have widely spaced wells. Using ASI we show how hydrothermal alteration affects drilling, and when used in conjunction with a predictive geologic model, how it will aid with optimisation of drilling practices through drill bit selection. Rock failure modes are difficult to predict, and are important to rock engineering environments, which include drilling. By using rock property and mineralogy information, four modes of failure were identified – axial splitting, single plane shearing, y shaped failure and multiple fracturing - in this research. The results of this study indicate that these easily measured rock properties can be inferred to have some control over the failure mode of a sample under uniaxial loading; however it would be useful to examine these samples further at the microstructural level to determine the role of microfracturing in the occurrence of failure modes. Further research in this field has the potential to aid in drilling optimisation through the utilisation of drill bits designed to fracture rocks in the ways that they are predisposed to fail.

Schichtung und Störungszonen sind typische Phänomene in Sedimentbecken wie dem Nordwestdeutschen Becken. Diese Gesteinsheterogenitäten können großen Einfluss auf viele verschiedene Fragestellungen im Zusammenhang mit der Exploration, dem Bohren und der hydraulischen Stimulation des geothermischen Reservoirs haben. Diese Doktorarbeit liefert Aussagen und Ansätze, wie hoch aufgelöste Daten, die in Aufschlüssen erhoben wurden, für eine verbesserte Vorhersage des Störungszonenaufbaus und der gesteinsmechanischen Eigenschaften in größeren Tiefen verwendet werden können. Um den Aufbau von Störungszonen und assoziierten Bruchsystemen in Sedimentgesteinen besser zu verstehen, wurden 58 Abschiebungen im Aufschlussmaßstab detailliert analysiert. Der Schwerpunkt lag dabei auf der Analyse von Bruchorientierung, -dichte, -öffnungsweite und -länge – jeweils getrennt betrachtet für Bruchzone und Nebengestein – sowie auf den strukturellen Indizes. Es konnten deutliche Unterschiede zwischen karbonatischen und klastischen Gesteinen festgestellt werden: in karbonatischen Gesteinen treten häufig ausgeprägte Bruchzonen mit erhöhten Bruchdichten auf. Während die maximale Öffnungsweite für beide Einheiten ähnlich ist, ist der Anteil an Brüchen mit großen Öffnungsweiten in der Bruchzone deutlich größer als im Nebengestein. In Karbonatgesteinen kann die Bruchorientierung in der Bruchzone stark von der im Nebengestein abweichen. In klastischen Gesteinen dagegen sind in beiden Einheiten ähnliche Bruchorientierungen zu finden. Die Auswertung der strukturellen Indizes zeigt, dass Abschiebungen in Karbonatgesteinen eher bruchzonen-dominiert sind als solche in klastischen Gesteinen und folglich größeren positiven Einfluss auf die Reservoirpermeabilität haben. Auf Basis der bestimmten Bruchdichtenverteilungen und Elastizitätsmoduli wurden effektive Steifigkeiten Ee innerhalb der Abschiebungen berechnet. Dabei zeigen Bruchzonen in klastischen Gesteinen eine deutlich geringere Abnahme der Steifigkeiten als solche in Karbonatgesteinen. Um die Kenntnisse über Eigenschaften typischer Gesteine im Nordwestdeutschen Becken zu erweitern, wurden physikalische (Vp-Geschwindigkeit, Porosität, Rohdichte und Korndichte) und gesteinsmechanische Parameter (Einaxiale Druckfestigkeit [UCS], Elastizitätsmodul, Zerstörungsarbeit und Zugfestigkeit; jeweils parallel und senkrecht zur sedimentären Schichtung) an 35 Gesteinsproben aus Aufschlüssen und 14 Bohrkernproben bestimmt. Für einen Teil dieser Proben (eine Vulkanit- sowie jeweils drei Sandstein- und Kalksteinproben) wurden Triaxialmessungen durchgeführt. Da Bohrkernmaterial selten ist, war es Ziel dieser Arbeit, die in-situ-Gesteinseigenschaften anhand von Aufschlussproben vorherzusagen. Die Eigenschaften von Proben aus größeren Tiefen werden dann mit denen äquivalenter Proben verglichen, d.h. Bohrkern und äquivalente Aufschlussprobe haben das gleiche stratigraphische Alter und eine vergleichbare sedimentäre Fazies. Die Äquivalenz der Proben wurde anhand von Dünnschliffen sichergestellt. Empirische Beziehungen bzw. Korrelationen zwischen UCS und allen physikalischen und geomechanischen Parametern wurden mit Regressionsanalysen bestimmt, jeweils lithologisch getrennt für alle Proben (inkl. Bohrkerne) und nur für Aufschlussproben. Die meisten Korrelationen haben ein hohes Bestimmtheitsmaß; die Ergebnisse der Bohrkerne liegen meist innerhalb der 90% Prognosebänder der Korrelationen, die für Aufschlussproben berechnet wurden. Auf ähnliche Weise wurden anhand von mehreren Triaxialmessungen pro Probe linearisierte Mohr-Coulomb Versagenskriterien bestimmt, die sowohl in Hauptnormalspannungen als auch in Normal- und Scherspannungen angegeben werden. Ein Vergleich zeigt, dass es zwar für Klastika und Vulkanite aus Aufschlüssen möglich ist, Versagenskriterien, die in Hauptnormalspannungen ausgedrückt werden, auf Bohrkernproben anzuwenden, aber nicht für Karbonate. Sind die Versagenskriterien allerdings in Normal- und Scherspannungen angegeben, ist die Anwendbarkeit für alle Gesteinsarten gut. Eine Übertragbarkeit der empirischen Beziehungen auf die Tiefe wird abgeleitet. Die wichtigsten Parameter, um die Anwendbarkeit der Aufschlussdaten zu gewährleisten, sind eine vergleichbare Textur und eine ähnliche Porosität von Äquivalenzproben aus Steinbrüchen und Bohrkernproben. Die Bruchausbreitung infolge einer hydraulischen Stimulation von heterogenen Gesteinen wurde mit dem Programm FRACOD analysiert. Es wurden numerische Modelle erstellt, die für das NWGB charakteristisch sind und die sowohl geschichtete Abfolgen als auch bereits existierende Brüche berücksichtigen. Die Ergebnisse der Untersuchung von Bruchsystemen in Störungszonen und die gemessenen gesteinsmechanischen Eigenschaften werden als Eingangsparameter verwendet. Die Modellierung zeigt, dass ein großer mechanischer Kontrast zwischen einzelnen Schichten bezüglich Elastizitätsmodul und Poissonkoeffizient geringeren Einfluss auf die Ausbreitungsrichtung des Bruches hat, als stark unterschiedliche Bruchzähigkeiten. Werden bereits existierende Brüche in das Modell eingebaut, zeigt sich eine starke Wechselwirkung mit dem induzierten Hydrobruch. Die Ergebnisse dieser Doktorarbeit sind von vielfältigem Nutzen. Erstens helfen die Daten bei der Exploration von geothermischen Reservoiren in Störungszonen mit hohen natürlichen Permeabilitäten. Zweitens liefern die Ergebnisse der Labormessungen Aussagen und Ansätze, wie man die mechanischen Gesteinseigenschaften in größeren Tiefen anhand von Aufschlussproben vorhersagen und sie als Eingangsparameter für zukünftige numerische Modellierungen zu geothermischen Fragestellungen heranziehen kann. Außerdem liefert die numerische Modellierung der Bruchausbreitung infolge einer hydraulischen Stimulation in heterogenen Gesteinen Einblicke in die relevanten Parameter, die Einfluss auf die Ausbreitungsrichtung des induzierten Bruches haben. Dieses Wissen wird dabei helfen, die hydraulische Stimulation an die jeweiligen Reservoirbedingungen anzupassen.

Hungary’s share of renewable energy in 2010 was 7.9 %, and their renewable energy goal for 2020 is 14.65 %. Geothermal energy is one option that could help to achieve the goal, since Hungary has favorable bedrock, the temperature gradient is above average and thepermeability is high. Today Hungary is importing just over half of its primary energy supply. Because of political conflicts between nations Hungary wants to expand its own production of energy. One of the major investments implemented was to build the largest geothermal heating plant in central Europe, located in Miskolc. This degree theses aims is to raise the capacity factor for this heating plant. To achieve this objective, a survey of how grain dryers and absorption chillers could increase the heat load in the summer has been performed. With grain dryers that only dries wheat, the capacity factor for the geothermal heating plant in Miskolc increased by 2.6 % and by 4.4 % for the absorption chiller. Although surveys have been carried out for a specific case the idea can be implemented in other heating plants. Keywords: Capacity factor, geothermal energy, wheat dryers and absorptions chiller.

Downhole sampling of unboiled liquid at 1350 and 1500 m depth in the seawater-dominated Reykjanes high-temperature geothermal system in Iceland shows that metal concentrations measured at surface are minimum values due to mineral precipitation in the wells; by analogy of similar tectonic setting, host rocks and fluid composition, the metal concentrations measured in many black smoker vents at the seafloor are also minima. Fluids in the Reykjanes geothermal system react with mid-ocean ridge basalt at temperatures as high as 346°C and contain Fe 9-140 ppm, Cu 14-17 ppm, Zn 5-27 ppm, Pb 120-290 ppb, 1-6 ppb Au, and 28-107 ppb Ag. Fluids discharged at surface from the same wells have orders of magnitude lower metal concentrations due to precipitation caused by boiling and vapor loss during depressurization. Upstream of the orifice plate at high pressure (40 bar, 252°C) the precipitates consist mainly of sphalerite and chalcopyrite with a trace of galena and bornite. At the orifice plate of old wells, the pressure decreased sharply to 11 bar (188°C), resulting in abundant deposition of amorphous silica together with minor sphalerite and traces of chalcopyrite. In new wells the pressure at the orifice plate decreases to 22 bar (220°C); this pressure decrease and concomitant boiling causes deposition of fine-grained bornite-digenite solid solution together with sphalerite and galena on the fluid flow control valve. In high-pressure wells (average wellhead pressure 45-35 bar) most metals (mainly as sphalerite) are deposited downstream of the orifice plate, with up to 950 ppm Au and 2.5 wt.% Ag. Bulk concentrations in the scales vary between 15-60 wt.% upstream and downstream of the orifice plate and diminish from there. Iron increases up well from 8 to ~20 wt.% and decreases downstream of the orifice plate from 6 to 2 wt.% at the separation station; Cu downhole is ~3 wt.% but increases to 25 wt.% on the fluid flow control valve and then decreases; Pb downhole 100s ppm but at the wellhead is ~3 wt.%, increasing to 15 wt.% at the fluid flow control valve, then decreasing sharply from there.

Im Freistaat Sachsen werden ca. 11.000 Gebäude mit Erdwärme klimatisiert. Genutzt wird die Wärme aus der Tiefe vor allem bei Ein- und Mehrfamilienhäusern zur Heizung und Warmwasserbereitung. Bei Planung und Bau von Erdwärmeanlagen sind Aspekte der Qualitätssicherung und rechtliche Vorgaben zu beachten. Interessierten Bürgern, Planern und Bohrfirmen werden u. a. folgende Fragen beantwortet: Welche Nutzungsformen der Erdwärme gibt es? Welche Qualitätsanforderungen, Richtlinien und Gesetze sind einzuhalten? Wie wird eine Anlage richtig geplant? Wo und wie werden Bohrungen bei Behörden beantragt?

Horizontal ground loop heat exchangers (GLHE) are widely used in many countries around the world as a heat source/sink for building conditioning systems. In Canada, these systems are most common in residential buildings that do not have access to the natural gas grid or in commercial structures where the heating and cooling loads are well balanced. These horizontal systems are often preferred over vertical systems because of the expense of drilling boreholes for the vertical systems. Current practice when sizing GLHEs is to add a considerable margin of safety. A margin of safety is required because of our poor understanding of in situ GLHE performance. One aspect of this uncertianty is in how these systems interact with heterogeneous soils. To investigate the impact of soil thermal property heterogeneity on GLHE performance, a specialized finite element model was created. This code avoided some of the common, non-physical assumptions made by many horizontal GLHE models by including a representation of the complete geometry of the soil continuum and pipe network. This model was evaluated against a 400 day observation period at a field site in Elora, Ontario and its estimates were found to be capable of reaching a reasonable agreement with observations. Simulations were performed on various heterogeneous conductivity fields created with GSLIB to evaluate the impact of structural heterogeneity. Through a rigorous set of experiments, heterogeneity was found to have little effect on the overall performance of horizontal ground loops over a wide range of soil types and system configurations. Other variables, such as uncertainty of the mean soil thermal conductivity, were shown to have much more impact on the uncertainty of performance than heterogeneity. The negative impact of heterogeneity was shown to be further minimized by: maintaining a 50 cm spacing between pipes in trenches; favouring multiple trenches over a single, extremely long trench; and/or using trenches greater than 1 m deep to avoid surface effects.