Dissertations / Theses on the topic 'Enhanced geothermal systems'

Micro-seismicity, and especially felt seismicity, induced by Enhanced Geothermal Systems (EGS) operations is a matter of scientific interest, not only because of the related risks and concerns, but also because the correspondence between injection and seismic activity still remains unclear. The Thesis aims to deepen the understanding of the involved Thermo-Hydro-Mechanical (THM) processes, in order to explain and manage co- and post-injection seismicity. First, we investigate the HM coupling and its effects on pressure response. Fluids injection exerts a force over the aquifer that causes deformation. This implies that Specific Storage, which reflects the capacity of permeable media to deform, cannot be treated as a single parameter, like in classical groundwater hydrology, because deformation also depends on aquifer geometry and on surrounding formations, which constrain displacements. We demonstrate the non-local nature of storage (i.e., its dependence on the poroelastic response over the whole aquifer) by means of analytical solutions to the transient pressure response to injection into one-dimensional and cylindrical finite aquifers, while acknowledging HM coupling. We find that the pressure response is faster and much greater than predicted with traditional solutions. Second, we consider non-isothermal injection and compare the effects of HM and TM couplings. We present analytical expressions for long-term hydraulic and thermal stresses and displacements for unidirectional and radial geometries. To obtain them, we assume steady-state fluid flow and develop an easy-to-use solution to the transient heat transport problem. The solution is then used to illustrate the poroelastic and thermoelastic response and, in particular, the sensitivity of stresses to the outer mechanical boundary conditions. Third, we perform coupled HM and THM simulations of cold water injection in a fault-intact rock system, which allows us to analyze mechanical stability changes during injection in the vicinity of the well. Simulation results show that temperature drop induces a significant perturbation of stresses in the intact rock near the injection well. This perturbation is likely to induce seismicity around critically oriented fractures. HM simulations show that fracture stability depends on the orientation of the faults and on the initial stress tensor. Results show that TM effects dominate and could induce seismicity, when the largest confining stress acts perpendicular to a fracture. Finally, we investigate the mechanisms that may induce seismicity after the end of fluid injection into a deep geothermal system (post-injection seismicity). Apart from the direct impact of fluid pressure increase, we acknowledge thermal effects due to cooling and stress redistribution caused by shear slip along favorably oriented fractures during injection. The effect of these three processes are analyzed both separately and superimposed. We find that post-injection seismicity may occur on unfavorably oriented faults that were originally stable. During injection, such faults become destabilized by thermal and shear slip stress changes, but remain static by the superposition of the stabilizing effect of pressure forces. However, these fractures become unstable and fail when the pressure forcing dissipates shortly after injection stops abruptly, which suggests that a slow reduction in injection rate may alleviate post-injection seismicity.
La micro-sismicitat induïda per operacions relacionades amb els Sistemes Geotèrmics Estimulats ha originat un gran interès científic, no només pel risc i la preocupació que comporta, sinó també perquè la relació entre la injecció de fluids i l'activitat sísmica no s'entén completament. Aquesta tesi pretén avançar en la comprensió dels processos hidro-termo-mecànics (THM) que causen aquesta sismicitat, per poder explicar-la i gestionar-la. En primer lloc, hem investigat l'acoblament hidro-mecànic (HM) i el seu efecte sobre les pressions. En Hidrologia Subterrània clàssica l'emmagatzematge especifico expressa la capacitat de l'aqüífer de deformar-se després d'una variació de pressió. Malgrat això, la sobrepressió generada per la injecció exerceix una força que deforma tot l'aqüífer, depenent de la seva geometria i de les formacions adjacents. Per això, l'emmagatzematge no es pot expressar amb un sol paràmetre, sinó que depèn de la resposta poro-elàstica de tot l'aqüífer, per la qual cosa diem que l'emmagatzematge específic és "no-local", cosa que vam mostrar mitjançant solucions analítiques de la resposta transitòria al problema HM de la injecció en aqüífers de dimensió finita, amb geometria tant unidimensional com cilíndrica. Seguidament, hem considerat una injecció no isoterma i comparat els efectes de l'acoblament hidro-mecànic (HM) i termo-mecànic (TM). Hem obtingut expressions analítiques per a les tensions i els desplaçaments induïts a llarg termini per la pertorbació hidràulica i tèrmica, en el cas de dominis unidireccional i radial. Per a això, hem considerat flux estacionari i desenvolupat una solució analítica senzilla per al transport de calor en règim transitori, la qual cosa ens ha permès calcular la resposta poro i termo-elàstica i en particular la sensibilitat de les tensions a les condicions mecàniques en el contorn exterior. A continuació, hem desenvolupat simulacions HM i THM acoblades de la injecció d'aigua freda en un sistema format per una falla embeguda en una roca intacta, a fi d'analitzar les variacions de l'estabilitat mecànica durant la injecció. Les simulacions HM mostren que l'estabilitat de les fractures depèn de la seva orientació i del tensor de tensions inicial. Concloem que la reducció de temperatura provoca prop del pou una forta pertorbació de les tensions, que pot induir sismes en fractures orientades críticament, especialment quan la tensió màxima actua perpendicularment a la fractura. Finalment, hem estudiat els mecanismes que poden induir sismes quan s'atura la injecció de fluids en sistemes geotèrmics profunds (sismicitat post-injecció). A més de l'efecte directe de l'augment de la pressió, hem considerat l'efecte tèrmic a causa del refredament i la redistribució de tensions generada pel moviment de cisalla que ocorre durant la injecció en fractures favorablement orientades. Aquests efectes s'han analitzat tant per separat com superposats. Dels resultats podem deduir que la sismicitat post-injecció pot ocórrer al llarg de fractures que eren inicialment estables i es desestabilitzen durant la injecció, a causa de les tensions tèrmiques i a les induïdes per la cisalla, però es mantenen estables gràcies a les forces de pressió. Posteriorment, aquestes fractures trenquen quan s'interromp la injecció, ja que les pressions es dissipen ràpidament. Això suggereix que la sismicitat post-injecció pot atenuar-se amb una reducció lenta del cabal d'injecció.

Geothermal energy has the potential to become a substantially greater contributor to the U.S. energy market. An adequate investment in Enhanced Geothermal Systems (EGS) technology will be necessary in order to realize the potential of geothermal energy. This study presents an optimization of a waterbased Enhanced Geothermal System (EGS) modeled for AltaRock Energy’s Newberry EGS Demonstration location. The optimization successfully integrates all three components of the geothermal system: (1) the present wellbore design, (2) the reservoir design, and (3) the surface plant design.

Since the Newberry EGS Demonstration will use an existing well (NWG 55-29), there is no optimization of the wellbore design, and the aim of the study for this component is to replicate the present wellbore conditions and design. An in-house wellbore model is used to accurately reflect the temperature and pressure changes that occur in the wellbore fluid and the surrounding casing, cement, and earth during injection and production. For the reservoir design, the existing conditions, such as temperature and pressure at depth and rock density, are incorporated into the model, and several design variables are investigated. The engineered reservoir is modeled using the reservoir simulator TOUGH2 while using the graphical interface PetraSim for visualization. Several fracture networks are investigated with the goal of determining which fracture network yields the greatest electrical output when optimized jointly with the surface plant. A topological optimization of the surface is completed to determine what type of power plant is best suited for this location, and a parametric optimization of the surface plant is completed to determine the optimal operating conditions.

The conditions present at the Newberry, Oregon EGS project site are the basis for this optimization. The subsurface conditions are favorable for the production of electricity from geothermal energy with rock temperatures exceeding 300°C at a well depth of 3 km. This research was completed in collaboration with AltaRock Energy, which has provided our research group with data from the Newberry well. The purpose of this thesis is to determine the optimal conditions for operating an Enhanced Geothermal System for the production of electricity at Newberry.

It was determined that a fracture network consisting of five fractured zones carrying 15 kg/s of fluid is the best reservoir design out of those investigated in this study. Also, it was found that 100 m spacing between the fractured zones should be implemented as opposed to only 50 m of spacing. A double-flash steam power plant provides the best method of utilization of the geothermal fluid. For the maximum amount of electricity generation over the 30-year operating lifetime, the cyclone separator should operate at 205°C and the flash vessel should operate at 125°C.

Thesis (S.M.)--Massachusetts Institute of Technology, Department of Civil and Environmental Engineering, 2013.
Cataloged from PDF version of thesis.
Includes bibliographical references (pages 167-171).
GEOFRAC is a three-dimensional, geology-based, geometric-mechanical, hierarchical, stochastic model of natural rock fracture systems. The main characteristic of GEOFRAC is that it is based on statistical input representing fracture patterns in the field in form of the fracture intensity P₃₂ (fracture area per volume) and the best estimate fracture size E[A]. Recent developments in GEOFRAC allow the user to calculate the flow in a fractured medium. For this purpose the fractures are modeled as parallel plates and the flow rate can be calculated using the Poisseuille equation. This thesis explores the possibility of the application of GEOFRAC to model a geothermal reservoir. After modeling the fracture flow system of the reservoir, it is possible to obtain the production flow rate. A parametric study was conducted in order to check the sensitivity of the output of the model. An attempt to explain how aperture, width and rotation (orientation distribution) of the fractures influence the resulting flow rate in the production well is presented. GEOFRAC is a structured MATLAB code composed of more than 100 functions. A GUI was created in order to make GEOFRAC more accessible to the users. Future improvements are the keys for a powerful tool that will let GEOFRAC to be used to optimize the location of the injection and production wells in a geothermal system.
by Alessandra Vecchiarelli.
S.M.

Cette recherche vise à étudier les impacts environnementaux d'une technologie émergente de production d’électricité basée sur une source renouvelable, les systèmes géothermiques stimulés (EGS), par l’analyse de leur cycle de vie (ACV).Après avoir analysé plusieurs études de cas, nous avons développé un modèle ACV paramétré capable de caractériser les performances environnementales de la filière EGS. Nos résultats montrent que les émissions de gaz à effet de serre des EGS sur leur cycle de vie sont bien inférieures à celles des centrales utilisant des combustibles fossiles.Dans un deuxième temps, nous avons mis au point un cadre méthodologique pour appliquer l'analyse de sensibilité globale (GSA) à l’ACV des technologies émergentes comme les EGS, prenant en compte les incertitudes élevées liées à leur caractère innovant. Nous avons appliqué notre nouvelle approche GSA pour développer un modèle ACV simplifié, à destination des décideurs, permettant une estimation rapide des impacts des EGS à partir de seulement cinq paramètres clefs: capacité installée, profondeur de forage, nombre de puits, débit géothermal et durée de vie.L'approche méthodologique développée dans cette thèse est applicable à d'autres technologies et ouvre de larges perspectives de recherche dans le domaine de l'évaluation environnementale
This thesis investigates the environmental impacts of an emerging renewable energy technology, the enhanced geothermal systems (EGS), using a life cycle assessment (LCA) approach.Following the analysis of several EGS case studies, we developed a parameterized LCA model able to provide a global overview of the life cycle impacts of the EGS technology. The greenhouse gas emissions of EGS are found comparable with other renewable energy systems and far better than those of power plants based on fossil fuels.In a second stage, we developed a methodological framework for the application of global sensitivity analysis (GSA) to the LCA of emerging technologies like the EGS, taking into account the high uncertainties related to their description. We applied our new GSA approach to generate a simplified LCA model, aimed at decision makers, allowing a rapid estimation of the life cycle impacts of EGS from only five key parameters: installed capacity, drilling depth, number of wells, flow rate and lifetime.The methodological approach developed in this thesis is applicable to other technologies and opens large research perspectives in the field of environmental assessment

The present work addresses the thermodynamic optimization of small binary-cycle geothermal power plants. The optimization process and entropy generation minimization analysis were performed to minimize the overall exergy loss of the power plant, and the irreversibilities associated with heat transfer and fluid friction caused by the system components. The effect of the geothermal resource temperature to impact on the cycle power output was studied, and it was found that the maximum cycle power output increases exponentially with the geothermal resource temperature. In addition, an optimal turbine inlet temperature was determined, and observed to increase almost linearly with the increase in the geothermal heat source. Furthermore, a coaxial geothermal heat exchanger was modeled and sized for minimum pumping power and maximum extracted heat energy. The geofluid circulation flow rate was also optimized, subject to a nearly linear increase in geothermal gradient. In both limits of the fully turbulent and laminar fully-developed flows, a nearly identical diameter ratio of the coaxial pipes was determined irrespective of the flow regime, whereas the optimal geofluid mass flow rate increased exponentially with the Reynolds number. SeveORCs were observed to yield maximum cycle power output. The addition of an IHE and/or an Oral organic Rankine Cycles were also considered as part of the study. The basic types of the FOH improved significantly the effectiveness of the conversion of the available geothermal energy into useful work, and increased the thermal efficiency of the geothermal power plant. Therefore, the regenerative ORCs were preferred for high-grade geothermal heat. In addition, a performance analysis of several organic fluids was conducted under saturation temperature and subcritical pressure operating conditions of the turbine. Organic fluids with higher boiling point temperature, such as n-pentane, were recommended for the basic type of ORCs, whereas those with lower vapour specific heat capacity, such as butane, were more suitable for the regenerative ORCs.
Dissertation (MEng)--University of Pretoria, 2013.
Mechanical and Aeronautical Engineering
unrestricted

Geothermal energy can make an important contribution to the U.S. energy portfolio. Production areas require seismic monitoring tools to develop and monitor production capability. This paper describes modifications made to a prototypical seismic tool to implement improvements that were identified during previous tool applications. These modifications included changing the motor required for mechanical coupling the tool to a bore-hole wall. Additionally, development of a closed-loop process control utilized feedback from the contact force between the coupling arm and bore-hole wall. Employing a feedback circuit automates the tool deployment/anchoring process and reduces reliance on the operator at the surface. The tool components were tested under high temperatures and an integrated system tool test demonstrated successful tool operations.
Master of Science

In this thesis, the potential of enhanced geothermal system to provide adequate energy to a 10 MW electricity power plant from Prairie Evaporite Formation of Williston Basin was investigated. This formation partly consists of halite with low thermal resistance and high thermal conductivity, which translates into a lower drilling length to reach the desired temperature, comparing to other rock types. To this end, two numerical models with experimental data in south-west Manitoba (i.e. Tilston) and south-east Saskatchewan (i.e. Generic) were designed. The thermal reservoirs were located at 1.5 km (Tilston site) and 3 km (Generic site) with approximate thicknesses of 118 m. Considering an injection brine of 6% NaCl at 15°C, the final derived temperature at wellhead of the production wells were 43°C and 105°C respectively. Finally, the Generic site was concluded as a suitable candidate for electricity production by providing higher surfaced fluid temperature than the minimum of 80°C.
February 2017

Enhanced geothermal systems (EGS) are emerging as an alternative energy supply, though progress has been slowed due to multiple uncertainties in subsurface processes. The most important unknown that needs to be overcome is how to spatially characterize injected fluids. Micro-seismic tomography can locate fractures opening caused by hydraulic pressure, but cannot directly discriminate whether that fracture is fluid filled or connected to other fractures. Magnetotellurics (MT) is sensitive to volumetric electrical conductivity contrasts with depth, specifically thermally enhanced saline fluids in a resistive host rock. Presented in this dissertation are 2 experiments designed for employing MT as a monitoring tool to characterize a fluid injection for the first stage of an EGS at Paralana, South Australia. The first experiment utilizes 11 MT stations set around the injection well continuously measuring 2 days before, 5 days during and 2 days after the fluid injection. Comparing the MT response estimated before the injection with subsequent responses estimated in 24 hour blocks demonstrates a temporal variation associated with injection of an electrically conductive fluid. Residual phase tensor analysis suggests that injected fluids migrated NE of the injection well in a preferred NNE direction, which correlates well with a concurrent micro-seismic array. The second experiment is a time-lapse MT survey that measures the MT response before and after the fluid injection by repeating the same 56 station array. The array contains 2 orthogonal lines of 22 stations each and 2 off diagonal lines of 6 stations each. Multiple pre-injection surveys were collected to ensure data precision and accuracy with a repeatability between surveys being on the order of 0.4 percent for periods above 1 second. However, in the MT dead band (1-20 s) repeatability is on the order of 3-4 percent. This is because of poor source signal and noise from a near by pipeline. The post-injection survey was collected a week after the injection finished and repeatability between pre and post-injection at high frequencies is on the order of 1 percent. Residual phase tensor analysis again suggest fluids propagated NE of the injection well but mostly into an existing fracture network trending NNE. These experiments suggest that MT can be used as a monitoring tool for a fluid injection, but care must be taken in collecting precise and accurate data as well as a detailed analysis of what can cause an anomalous MT response. Residual phase tensor analysis proves to be the most useful representation of the MT response because it provides directionality and is insensitive to near surface distortions. Finally, it is suggested that a dense grid of MT and micro-seismic measurements be collected as complimentary pairs to fully characterize a fluid injection.
Thesis (Ph.D.) -- University of Adelaide, School of Earth and Environment Sciences, 2012

Engineered Geothermal System (EGS) has great potential to supply electricity by harnessing stored thermal energy from high temperature granitic rocks. Since reserves of coal, oil, and natural gas are being depleted at an increasing rate, this route provides opportunities to generate electrical power without producing greenhouse gas emissions or long lasting nuclear wastes, at a cost that is competitive to those generated from fossil fuels. Australia has a vast amount of thermal area, though the heat exchange occurs at a significantly greater depth (5 km) to conventional geothermal system. Clearly, the study of fluid-rock interaction is crucial and remains largely poorly addressed and known. A compounding factor is the fact that fundamental processes associated with mineral dissolution and precipitation, and the developed pressure temperature gradient remain poorly understood. Furthermore, a number of issues relating to geothermal geochemistry are required to be considered and explored to ensure safe, economic energy production from the “hot rocks”. Low pH and saline waters at temperatures exceeding 200°C are highly corrosive. Thus, it is vital to prevent the generation of scaling as the brines cool during transport to the surface. The objectives of this study were to investigate the geochemistry, the fluid-rock interaction, and model the precipitation rate of silica. Experimental work was carried out to observe the fluid-rock interaction, including analysis on the rock to monitor the dissolved elements in the circulating fluid, and the water chemistry after the interaction. The granite samples were analysed using x-ray diffraction and results showed that the rock consist of mainly quartz, albite and K-feldspar. This study concentrated on the dissolution rate of granite by observing the silica concentration in the liquid phase with the aid of previous dissolution rate studies of pure quartz, albite and K-feldspars (Rimstidt and Barnes, 1980; Hellmann, 1994; Worley, 1994; Brantley, 2008; Brown, 2011b). In order to investigate the fluid-rock interaction in the Cooper Basin geothermal system (i.e. Habanero 3 well), three experimental methods at a laboratory scale were developed. To simplify the process, the gas phases were not introduced to the system. The first method allows the interaction of fluid and rock samples in a closed system where no fluid is required to be replaced (fluid mass is constant) during the experimental period. The experiment is conducted in Teflon lined autoclaves for different interaction periods and the maximum temperature chosen was 220°C due to the limitation of the Teflon liners used. This method was used firstly to obtain the equilibrium silica concentration at various temperatures. The experimental results showed good agreement with the literature values. The equilibrium silica concentrations obtained from dissolution at 120°C, 140°C, 160°C, 170°C, 200°C and 220°C for 56 days were 56 ± 3 ppm, 94 ± 6 ppm, 137 ± 6 ppm, 175 ± 7 ppm, 282 ± 11 ppm, and 350 ± 28 ppm, respectively. The second observation was the dissolution kinetics in pure water. The SigmaPlot software was used to fit the experimental data and obtain the equilibrium silica concentration and silica dissolution rate constant based on a first order global rate equation by Worley (1994). The results were compared with a compiled quartz dissolution literature values and showed good agreement, however values differ slightly due to the different materials and experimental conditions. The obtained dissolution rate constants were then regressed using the Arrhenius equation describing a kinetic rate constant with an activation energy of 64.53 kJ/mol. A number of factors affecting the dissolution rate of granite were observed. One factor was the effect of particle size on the dissolution rate of granite. The experimental results agree with literature, which demonstrated that the dissolution rates increased with decreasing granite particle size (increasing the surface area). Another observation undertaken was the effect of electrolyte (250 ppm NaCl solution) on the granite dissolution rate. The results concluded that the dissolution rate in 250 ppm NaCl solution yielded a two-fold increase compared to that in pure water. One other observation was on the effect of pH in granite dissolution rate. The experimental results agree with the literature confirming that the increase of dissolution rates at lower pH was due to the presence of organic acid (acetic acid) in the pH buffer used. At pH above 8 the dissolved silica species that is significant is not solely SiO₂(aq) [(aq) subscript] (H₄SiO₄). The hydrogen atoms from H₄SiO₄ can dissociate and release H₃SiO₄⁻ ion which is very soluble in water. As the pH increase, further hydrogen dissociation is possible to form H₂SiO₄²⁻ which is also soluble in water and thus increasing the silica concentration, leading to an increased dissolution rate. The second method used a closed loop batch flow-through cell that was designed to mimic the circulation of the fluid-rock interaction hence enabling the observation of the changes in the chemical properties of the host rock and circulating fluid that may occur. This method involved two different experimental systems. The first system allows the continuous interaction of the fluid (pure water and 250 ppm NaCl solution) and rock samples at 250°C (close to the actual geothermal reservoir temperature) to study the dissolution kinetics of silica from the granite for different interaction periods. This system was also used to study the effect of fluid/rock ratio. The experimental results agree with the literature which illustrate a decrease in solid/liquid ratio (increase in fluid/solid ratio) would increase the reaction rate. The second system allows the interaction of fluid and rock samples also in a closed loop batch flow-through cell, using pure water and 250 ppm NaCl solution for 7 days and 28 days, and the fluid is consistently replaced every 24 hours for the specified interaction periods. This system was designed to accelerate the mineral dissolution to observe which minerals were more soluble. SEM results revealed that severe pitting exists on the surface of the granite, as a consequence of rapid dissolution, and it was observed that fine particles were present between and on the surface of the granite which increased the particles surface area, enhancing the dissolution rate. The SEM back-scatter images revealed albite as the more soluble phase, since more cavities were observed through the albite phases compared to the K-feldspar phases in the granite samples. The third method involved a high pressure open loop flow through system, where fresh water is continuously injected to the system. This system was configured to observe the influence of pressure in rock water interaction. Three pressure conditions at 250°C were chosen (at vapour pressure, 100 bars, and 200 bars). The experimental results showed that the silica concentration increased with pressure, agreeing with the published literatures. In order to validate the experimental results, the React program from the Geochemist Workbench software was used to simulate the granite dissolution reaction path and generate silica dissolution and silica precipitation rates. The simulation in React is based on the transition state theory model (Rimstidt and Barnes, 1980; Bethke, 1996). The results of the modelling showed consistent plots with the experimental results however generated different values of rate constants and equilibrium silica concentrations. React was also used to calculate the amount or rate of silica precipitation with the assumption that the aperture of the fracture was 10 cm and the surface roughness was 2. For granite dissolution in pure water, the amount of silica that may precipitate was approximately 298 mg/28 days, and in 250 ppm NaCl solution is 309 mg/28 days. From the available information, the sealing rate from granite dissolution in water was 2.30 cm/1000 years, and that in NaCl solution was 2.41 cm/1000 years. Since this was a simplified model and only the major components of the granite were included, it may have influenced the reaction path calculated by React, affecting the silica concentration output and reaction rate. Another contributing factor may be that the active surface area of the granite in the experiment differs with the BET surface area obtained in this study. In addition, the published reaction rate constant may have different experimental conditions (e.g. different composition of minerals, particle size, duration of experiments, different reactors). As well, the input of the reaction rate constant was allowed for single minerals, and the model may not simulate the exact laboratory experimental conditions. Moreover, this study measured the dissolution of granite solely from the release of silica to the solution. Since the literature published reaction rate constant from pure minerals (e.g. albite), this reaction rate constant may not be the appropriate value to specify the albite component in the granite. In other words, the reaction path of dissolving three pure minerals in water may not be identical to the dissolution mechanism of granite with the same mineral composition. Since the model output resulted in some differences compared to the experimental results, this suggests that modelling and experiments should work together to predict more accurate outputs.
Thesis (Ph.D.) -- University of Adelaide, School of Chemical Engineering, 2015

Dissertação de Mestrado Integrado em Engenharia Mecânica apresentada à Faculdade de Ciências e Tecnologia da Universidade de Coimbra
Tradicionalmente, o aproveitamento da energia geotérmica para produção de energia eléctrica limitava-se a locais onde o vapor e/ou as águas muito quentes emergiam à superfície. Recentemente, com o avanço da tecnologia começaram-se a desenvolver-se novos sistemas de captação desta energia tendo surgido os sistemas geotérmicos estimulados (SGE) que permitem produzir energia eléctrica em qualquer parte do mundo, mesmo em locais com baixas entalpias. A aplicação de um SGE torna-se assim numa excelente oportunidade para produção de energia eléctrica, na Região Centro de Portugal, local dominado por baixas entalpias. Ao longo desta dissertação, procura-se analisar os custos associados a estes sistemas e avaliar a influência das variáveis chave, como a profundidade, o gradiente de temperatura do solo em profundidade e o caudal na viabilidade económica da instalação de um SGE nesta região. Neste estudo é testada a viabilidade de cinco profundidades (3,0; 3,5; 4,0; 4,5 e 5,0 km) para implantação de um SGE. Para cada uma das profundidades são assumidas quatro variações de temperatura por quilómetro de profundidade (30; 35; 40 e 45 ºC/km) e um caudal de 30 L/s. Através de pressupostos técnicos, económicos e financeiros, é determinada a viabilidade da aplicação de um sistema geotérmico estimulado na Região Centro de Portugal. Concluiu-se que as situações com maior rentabilidade económica estão associadas aos maiores aumentos da temperatura com a profundidade. Assumindo uma tarifa líquida de 0,25 €/kWh e que são rentáveis os investimentos com um Período de Retorno (PR) inferior a 15 anos, afiguram-se como viáveis as situações com gradientes de temperatura superiores a 35 ºC/km para uma profundidade de 5,0 km, com gradientes a partir dos 40 ºC/km para furos de 4,5 km e acima de 45 ºC/km para profundidades iguais ou superiores a 3,5 km. Não é viável instalar um SGE em locais com gradientes de temperatura inferiores a 35 ºC/km. O recurso a profundidades inferiores a 3,5 km só será eventualmente viável para gradientes de temperatura superiores a 50 ºC/km, mas este caso não foi analisado no decurso deste trabalho.
Traditionally, the exploitation of geothermal energy for electrical energy production was limited to areas where steam and/or hot water emerged to the surface. Recently, with the technological advancements new systems of energy collection started to appear, having emerged the enhanced geothermal systems (EGS), which allow the production of electrical energy in any part of the world, even in areas with low enthalpy. The application of an EGS becomes an excellent opportunity for production of electrical energy, in Central Region of Portugal, an area dominated by low enthalpy. This dissertation aims to analyze the costs associated with these systems and evaluate the influence of the key variables, such as depth, gradient of soil temperature in depth and flow rate on the economic feasibility of installing an EGS in this region. This study tests the feasibility of five different depths (3,0; 3,5; 4,0; 4,5 e 5,0 km) for the implementation of an EGS. For each of the different depths are assumed four in-depth temperature gradients (30; 35; 40 e 45 ºC/km) and a flow rate of 30 L/s. Through technical, economic and financial assumptions, the feasibility of the application of an EGS in the central region of Portugal is assessed. It was concluded that situations with higher economical profitability are associated to the largest increases of temperature with depth. Assuming a net rate of 0,25 €/kWh and that investments with a Return Period (RP) under 15 years are profitable, it is predicted to be feasible in situations with temperature gradients above at 35 ºC/km to a depth 5,0 km, with gradients from 40 ºC/km and holes of 4,5 km, and greater than or equal gradients at 45 ºC/km to depth 3,5 km. It is not feasible to install an EGS in places with temperature gradients of less than 35 °C/km. The use of less than 3,5 km of depth is eventually viable for gradients exceeding 50 °C/km temperature, although this case was not examined during this study.

This item is only available electronically.
The global demand for clean energy alternatives is constantly increasing, creating significant interest for more sustainable energy resources such as uranium and geothermal. Australia is host to over 25% of the world's known uranium resources as well as having significant geothermal potential. The Mount Painter Domain, in the Northern Flinders Ranges in South Australia, is in a region of anomalously high heat flow generated by radiogenic decay of uranium and thorium rich granites. Two distinct uranium deposits have formed from dissolved uranium carried from the ranges by fluids, being deposited where reduction in sediment pH precipitates uranium. In May 2012 a magnetotelluric profile was collected, extending from the Northern Flinders Ranges to the Lake Frome embayment to help constrain existing resistivity models. Precipitation of uranium at the Beverley Mine site is anomalous as no surface water flow is present, suggesting the presence of subsurface processes. This pathway is linked to a 50m conductive body at the brittle-ductile boundary of the mid-crust, directly under the Paralana geothermal prospect. 3D modelling of the Paralana geothermal prospect suggests deep conductive features connecting with features at the surface.
Thesis (B.Sc.(Hons)) -- University of Adelaide, School of Earth and Environmental Sciences, 2012

Multistage hydraulic fracturing of horizontal wells continues to be a major technological tool in the oil and gas industry. Creation of multiple transverse fractures in shale gas has enabled production from very low permeability. The strategy entails the development of a Stimulated Reservoir Volume (SRV), defined as the volume of reservoir, which is effectively stimulated to increase the well performance. An ideal model for a shale gas SRV is a rectangle of length equal to horizontal well length and width equal to twice the half length of the created hydraulic fractures. This project focused on using the Multistage Transverse Fractured Horizontal Wells (MTFHW) for two novel applications. The first application considers using the SRV of a shale gas well, after the gas production rate drops below the economic limit, for low grade geothermal heat extraction. Cold water is pumped into the fracture network through one horizontal well drilled at the fracture tips. Heat is transferred to the water through the fracture surface. The hot water is then recovered through a second horizontal well drilled at the other end of the fracture network. The basis of this concept is to use the already created stimulated reservoir volume for heat transfer purposes. This technique was applied to the SRV of Haynesville Shale and the results were discussed in light of the economics of the project. For the second application, we considered the use of a similarly created SRV for producing hydrocarbon products from oil shale. Thermal decomposition of kerogen to oil and gas requires heating the oil shale to 700 degrees F. High quality saturated steam generated using a small scale nuclear plant was used for heating the formation to the necessary temperature. Analytical and numerical models are developed for modeling heat transfer in a single fracture unit of MTFHW. These models suggest that successful reuse of Haynesville Shale gas production wells for low grade geothermal heat extraction and the project appears feasible both technically and economically. The economics of the project is greatly aided by eliminating well drilling and completion costs. The models also demonstrate the success of using MTFHW array for heating oil shale using SMR technology.

In geothermal reservoirs and unconventional gas reservoirs with very low matrix permeability, fractures are the main routes of fluid flow and heat transport, so the fracture permeability change is important. In fact, reservoir development under this circumstance relies on generation and stimulation of a fracture network. This thesis presents numerical simulation of the response of a fractured rock to injection and extraction considering the role of poro-thermoelasticity and joint deformation. Fluid flow and heat transport in the fracture are treated using a finite difference method while the fracture and rock matrix deformation are determined using the displacement discontinuity method (DDM). The fractures response to fluid injection and extraction is affected both by the induced stresses as well as by the initial far-field stress. The latter is accounted for using the non-equilibrium condition, i.e., relaxing the assumption that the rock joints are in equilibrium with the in-situ stress state. The fully coupled DDM simulation has been used to carry out several case studies to model the fracture response under different injection/extractions, in-situ stresses, joint geometries and properties, for both equilibrium and non-equilibrium conditions. The following observations are made: i) Fluid injection increases the pressure causing the joint to open. For non-isothermal injection, cooling increases the fracture aperture drastically by inducing tensile stresses. Higher fracture aperture means higher conductivity. ii) In a single fracture under constant anisotropic in-situ stress (non-equilibrium condition), permanent shear slip is encountered on all fracture segments when the shear strength is overcome by shear stress in response to fluid injection. With cooling operation, the fracture segments in the vicinity of the injection point are opened due to cooling-induced tensile stress and injection pressure, and all the fracture segments experience slip. iii) Fluid pressure in fractures increases in response to compression. The fluid compressibility and joint stiffness play a role. iv) When there are injection and extraction in fractured reservoirs, the cooler fluid flows through the fracture channels from the injection point to extraction well extracting heat from the warmer reservoir matrix. As the matrix cools, the resulting thermal stress increases the fracture apertures and thus increases the fracture conductivity. v) Injection decreases the amount of effective stress due to pressure increase in fracture and matrix near a well. In contrast, extraction increases the amount of effective stress due to pressure drop in fracture and matrix.