One of the most applicable methods of low-temperature geothermal resource assessment is volumetric method. While applying volumetric method, the values of uncertain parameters should be determined. An add-in software program to Microsoft EXCEL, @RISK, is used as a tool to define the uncertainties of the parameters in volumetric equation. In this study, Monte Carlo simulation technique is used as the probabilistic approach for the assessment of lowtemperature Bal&ccedil / ova-Narlidere geothermal field. Although Bal&ccedil / ova-Narlidere geothermal field is being utilized for several direct heat applications, there exists limited data for resource assessment calculations. Assessment studies using triangular and uniform distribution type functions for each parameter gave the mean values of recoverable heat energy of the field as 25.1 MWt and 27.6 MWt, respectively. As optimistic values (90%), those values were found as 43.6 MWt and 54.3 MWt. While calculating these numbers, a project life of 25 years with a load factor of 50% is used.

ABSTRACT CHARACTERIZATION OF KIZILCAHAMAM GEOTHERMAL FIELD BY TRACER TESTING Tevfik Kaya M.S, Petroleum and Natural Gas Engineering Department Supervisor : Assoc. Prof. Dr. Serhat Akin Co-Supervisor : Prof. Dr. Mahmut Parlaktuna September 2005, 107 Pages Kizilcahamam Geothermal Field which is 70 km far from Ankara, has been utilized for Geothermal District Heating System, 25 MWt, 2500 residences capacity, greenhouses heating, thermal facilities since 1994. The average production rate is 350m3/h during the heating season , 150m3/h during the summer season for hot water and yearly average reinjection rate is 114m3/h from the field. The long term projections has been studied concerning on expected pressure decline by matching 10 years field history data which contain dynamic level and temperature data. The pressure decline is 140 kPa in the field between 1999 and 2005 with the existing reinjection rate, if the existing rates do not change, the additional pressure decline which is 120 kPa will be occurred up to 2011. In order to get more information from the field, the fluorescein as tracer has been injected in to the MTA-1, and the samples were collected from the MTA-2, Fethi Bey, IHL-1 and IHL-3 for 3 months. The fluorescein concentration has been detected by using fluorimeter, and tracer concentration time plots were analyzed. The fluoreiscein was detected in short breakthrough time in MTA-2 and Fethi Bey which are close to reinjection well, breakthrough time is longer in IHL-1 and IHL-3. The interpretation of tracer test shows that there is communication between all wells. Tracer concentration time plots were compared with different mathematical models, the best match was obtained with multi-fractured model. These results show that Kizilcahamam field is not homogeneous field. It is expected that increasing the reinjection rate will decrease the pressure decline in the field.

No description available.

Geothermal energy is the energy naturally present inside the earth crust. When a large volume of hot water and steam is trapped in subsurface porous and permeable rock structure and a convective circulating current is set up, it forms a geothermal reservoir. A geothermal system can be defined as - convective water in the upper crust of earth, which transfers heat from a heat source (in the reservoir) to a heat sink, usually the free surface. A geothermal system is made up of three main elements: a heat source, a reservoir and a fluid, which is the carrier that transfers the heat. As an alternative source of energy geothermal energy has been under attention of the researchers for quite some time. The reason behind this is the existence of several benefits like clean and renewable source of energy which has considerable environmental advantage, with no chemical pollutants or wastes are generated due to geothermal emissions, and the reliability of the power resource. Hence research has been directed in several directions like exploration of geothermal resources, modeling the characteristics of different types of geothermal reservoirs and technologies to extract energy from them. The target of these models has been the prediction of the production of the hot water and steam and thus the estimation of the electricity generating potential of a geothermal reservoir in future years. In a geothermal power plant reinjection of the heat depleted water extracted from the geothermal reservoir has been a common practice for quite some time. This started for safe wastewater disposal and later on the technology was employed to obtain higher efficiency of heat and energy extraction. In most of the cases a very small fraction of the thermal energy present in the reservoir can be recovered without the reinjection of geothermal fluid. Also maintaining the reservoir pressure is essential which gradually reduces due to continuous extraction of reservoir fluid without reinjection, especially for reservoirs with low permeabilities. Although reinjection of cold-water has several benefits, the possibility of premature breakthrough of the cold-water front, from injection well zone to production well zone, reduces the efficiency of the reservoir operation drastically. Hence for maintaining the reservoir efficiency and longer life of the reservoir, the injectionproduction well scheme is to be properly designed and injection and extraction rates are to be properly fixed. Modeling of flow and heat transport in a geothermal reservoir due to reinjection of coldwater has been attempted by several researchers analytically, numerically and experimentally. The analytical models which exist in this field deal mostly with a single injection well model injecting cold-water into a confined homogeneous porous-fractured geothermal reservoir. Often the thermal conductivity is neglected in the analytical study considering it to be negligible which is not always so, as proved in this study. Moreover heterogeneity in the reservoir is also a major factor which has not been considered in any such analytical study. In the field of numerical modeling there also exists a need of a general coupled three-dimensional thermo-hydrogeological model including all the modes of heat transport (advection and conduction), the heat loss to the confining rocks, the regional groundwater flow and the geothermal gradient. No study existing so far reported such a numerical model including those mentioned above. The present study is concerned about modeling the non-isothermal flow and heat transport in a geothermal reservoir due to reinjection of heat depleted water into a geothermal reservoir. Analytical and numerical models are developed here for the transient temperature distributions and advancement of the thermal front in a geothermal reservoir which is generated due to the cold-water injection. First homogeneous geothermal aquifers are considered and later heterogeneities of different kinds are brought into picture. Threedimensional numerical models are developed using a software code DuMux which solves flow and heat transport problems in porous media and can handle both single and multiphase flows. The results derived by the numerical models have been validated using the results from the analytical models derived in this study. Chapter 1 of the thesis gives a brief introduction about different types of geothermal reservoirs, followed by discussion on the governing differential equations, the conceptual model of a geothermal reservoir system, the efficiency of geothermal reservoirs, the modeling and simulation concepts (models construction, boundary conditions, model calibration etc.). Some problems related with geothermal reservoirs and geothermal power is also discussed. The scenario of India in the context having a huge geothermal power potential is described and different potential geothermal sites have been pointed out. In Chapter 2, the concept of reinjection of the heat depleted (cold) water into the geothermal reservoir is introduced. Starting with a brief history of the geothermal reinjection, the chapter describes the purpose and the need of reinjection of geothermal fluid giving examples of different geothermal fields over the world where reinjection has been in practice and benefitted by that. The chapter further discusses on the problems and obstacles faced by the geothermal projects resulting from the geothermal reinjection, most important of which is the thermal-breakthrough and cooling of production wells. Lastly the problem of this thesis is discussed which is to model the transient temperature distribution and the movement of the cold-water thermal front generated due to the reinjection. The need of this modeling is elaborated which represents the motivation of taking up the problem of the thesis. Chapter 3 describes an analytical model developed for the transient temperature in a porous geothermal reservoir due to injection of cold-water. The reservoir is composed of a confined aquifer, sandwiched between rocks of different thermo-geological properties. The heat transport processes considered are advection, longitudinal conduction in the geothermal aquifer, and the conductive heat transfer to the underlying and overlying rocks of different geological properties. The one-dimensional heat transfer equation has been solved using the Laplace transform with the assumption of constant density and thermal properties of both rock and fluid. Two simple solutions are derived afterwards, first neglecting the longitudinal conductive heat transport and then heat transport to confining rocks. The analytical solutions represent the transient temperature distribution in the geothermal aquifer and the confining rocks and model the movement of the cold-water thermal front in them. The results show that the heat transport to the confining rocks plays an influential role in the transient heat transport here. The influence of some parameters, e.g. the volumetric injection rate, the longitudinal thermal conductivity and the porosity of the porous media, on the transient heat transport phenomenon is judged by observing the variation of the transient temperature distribution with different values of the parameters. The effects of injection rate and thermal conductivity have been found to be high on the results. Chapter 4 represents another analytical model for transient temperature distribution in a heterogeneous geothermal reservoir underlain and overlain by impermeable rocks due to injection of cold-water. The heterogeneity of the porous medium is expressed by the spatial variation of the flow velocity and the longitudinal effective thermal conductivity of the medium. Simpler solutions are also derived afterwards first neglecting the longitudinal conduction, then the heat loss to the confining rocks depending on the situation where the contribution of them to the transient heat transport phenomenon in the porous media is negligible. Solution for a homogeneous aquifer with constant values of the rock and fluid parameters is also derived with an aim to compare the results with that of the heterogeneous one. The effect of heat loss to the confining rocks in this case is also determined and the influence of some of the parameters involved, on the transient heat transport phenomenon is assessed by observing the variation of the results with different magnitudes of those parameters. Results show that the heterogeneity plays a major role in controlling the cold-water thermal front movement. The transient temperature distribution in the geothermal reservoir depends on the type of heterogeneity. The heat loss to the confining rocks of the geothermal aquifer also has influence on the heat transport phenomenon. In Chapter 5 another analytical model is derived for a heterogeneous reservoir where the heterogeneous geothermal aquifer considered is a confined aquifer consisted of homogeneous layers of finite length and overlain and underlain by impermeable rock media. All the different layers in the aquifer and the overlying and underlying rocks are of different thermo-hydrogeological properties. Results show that the advancement of the cold-water thermal front is highly influenced by the layered heterogeneity of the aquifer. As the cold-water thermal front encounters layers of different thermo-hydrogeological properties the movement of it changes accordingly. The analytical solution derived here has been compared with a numerical model developed by the multiphysics software code COMSOL which shows excellent agreement with each other. Lastly it is shown that approximation of the properties of a geothermal aquifer by taking mean of the properties of all the layers present will lead to erroneous estimation of the temperature distribution. Chapter 6 represents a coupled three-dimensional thermo-hydrogeological numerical model for transient temperature distribution in a confined porous geothermal aquifer due to cold-water injection. This 3D numerical model is developed for solving more practical problems which eliminate the assumptions taken into account in analytical models. The numerical modeling is performed using a software code DuMux as mentioned before. Besides modeling the three-dimensional transient temperature distribution in the model domain, the chapter investigates the regional groundwater flow has been found to be a very important parameter to consider. The movement of the thermal front accelerates or decelerates depending on the direction of the flow. Influence of a few parameters involved in the study on the transient heat transport phenomenon in the geothermal reservoir domain, namely the injection rate, the permeability of the confining rocks and the thermal conductivity of the geothermal aquifer is also evaluated in this chapter. The models have been validated using analytical solutions derived in this thesis. The results are in very good agreement with each other. In Chapter 7 the main conclusions drawn from the study have been enlisted and the scope of further research is also pointed out.

No description available.

The effectiveness of the heat transfer in a geothermal reservoir strongly depends on its temperature, pressure and rock type. A porous and fractured rock is essential to provide a hot fluid circulation to a geothermal power plant. Velocity anomalies in seismic tomography may relate to the location of a fluid reservoir, hydrothermal systems, and possible heat sources. However, the subsurface properties like porosity, fracture density, and fluid state (e.g liquid, gas or supercritical fluid) cannot be inferred directly using seismic tomography. The inversion of seismic data can be combined with an effective medium model (EMM) to investigate such rock and subsurface properties. In the present study, we implement an EMM involving elastic rock properties and the following descriptions of inclusions: pore porosity, fracture density, fracture aspect ratio, fracture porosity, and liquid ratio. The chosen EMM was reproduced from the work of Adelinet et al. (2011a) and Adelinet (2010). Tomographic results were inverted for the same geographic area (Krysuvik in Iceland) in order to validate our method and to confirm the presence of the supercritical fluid reservoir. We re-evaluate the assumptions and constraining parameters choice of the inverse model used in Adelinet et al. (2011a) and Adelinet (2010), in order to 1) get a better understanding of the underlying problems, 2) investigate the sensitivity of the results based on the constraining parameters, 3) produce suitable workflows, and 4) build an adaptive method for geothermal exploration in different areas. The newly implemented method found the same qualitative results in Krysuvik as Adelinet et al. (2011a). Namely, at ≈ 6.5 km depth both values of fracture density and of liquid ratio are consistent with hydraulic fracturing and a probable super-critical fluid reservoir. Afterwards, the method was applied to the Hengill volcanic complex. Fracture density and liquid ratio values similar to those observed at Krysuvik and associated to a geothermal reservoir were obtained at Hengill at the exact location of existing production sites. Our results also showed limitations of initial assumptions and could contribute to improve the method. This study could be a starting point to build a more sophisticated tool for geothermal exploration. / Idag består majoriteten av världens energiproduktion av fossilt bränsle. Naturgas, kol och olja stod tillsammans för 70% av världens energiproduktion 2010 och det ökar konstant trots nödvändigheten att minska koldioxidutsläppen. Geotermisk energi är en hållbar resurs men bidrar endast med mindre än 2% av världens energi. Det finns dock undantag, exempelvis på Island där 70% av all energi som förbrukas kommer från geotermiska resurser. Island är en seismiskt aktiv region som inkluderar diverse olika geotermiska områden med hög temperatur. På grund av detta, har det där skett mycket forskning om geotermiska resurser. Vidare information är nödvändig för att utforska potentialen av att nyttja geotermisk energi. I denna studie impementerades en metod som kombinerar seismiska hastigheter och teoretiska mekaniska egenskaper av stenar, exempelvis stenbrottsgeometri. Metoden tillåter att uttyda egenskaper under ytan, framförallt tätheten av sprickor och det fysiska tillståndet av vätskan. Dessa egenskaper kan bidra med relevant information för beslutstagande och är nödvändiga för att lyckas med borrning. En optimering av mätna och teoeriska värden var beräknad för att hitta de optimala värdena av spricktäthet och det fysiska tillståndet av vätskan. Studien fokuserar huvudsakligen på två geotermiska områden på Island, Krysuvik- och Hengill-vulkanernas områden. Resultat erhållna från Krysuvik konfimerade en möjlig superkritisk vätskereservoar på ettdjup av 5.5-6.5 kilometer. Efter att ha studerat Hengill-området, uppkom resultat på den geotermiska utvinningsplatsen men det visade även begränsningar kring metoden. Metoden behöver förbättras och anpassa sig till funktionen av området. Heterogeniteten och de komplexa egenskaperna (till exempel bergskomposition eller vätskealternering) under ytan ledde till omvärdering av antaganden gjorda i den initiala mediummodellen.

Für eine effiziente und nachhaltige Nutzung von Georeservoiren sind bestmögliche Reservoirmanagementverfahren erforderlich. Oft setzen diese Verfahren auf Tracer-Tests. Dabei enthalten die aufgezeichneten Tracersignale integrale Informationen der Reservoireigenschaften. Tracer-Tests bieten somit eine leistungsfähige Technik zur Charakterisierung und Überwachung der bewirtschafteten Georeservoire. Im Gegensatz zu Tracer-Tests mit konservativen Tracern, welche bereits etablierte Testroutinen zur Verfügung stellen, ist die Verwendung von reaktiven Tracern ein neuer Ansatz. Aufgrund unpassender physikalisch-chemischer Modelle und/oder falschen Annahmen ist die Analyse und Interpretation von reaktiven Tracersignalen jedoch oft verzerrt, fehlinterpretiert oder sogar unmöglich. Reaktive Tracer sind dennoch unersetzbar, da sie durch die gezielte Ausnutzung selektiver und spezifischer Reaktionen mögliche Metriken von Reservoirtestverfahren auf einzigartige Weise erweitern. So liefern reaktive Tracer für ein integriertes Reservoirmanagement geforderten Aussagen über Reservoirmetriken wie z.B. Wärmeaustauschflächen oder in-situ Temperaturen. Um Unsicherheiten bei der Auswertung von Tracerexperimenten zu reduzieren, werden theoretische und experimentelle Untersuchungen zu hydrolysierenden Tracern vorgestellt. Diese Tracer sind durch ihre Reaktion mit Wasser charakterisiert. Einerseits können sie als thermo-sensitive Tracer Informationen über Temperaturen und abgekühlte Anteile eines beprobten Reservoirs liefern. Für die Interpretation von thermo-sensitiven Tracerexperimenten sind die Kenntnis der zugrunde liegenden Reaktionsmechanismen sowie bekannte Arrhenius-Parameter Voraussetzung, um die verwendete Reaktion pseudo erster Ordnung nutzen zu können. Darüber hinaus ermöglichen die verwendeten Verbindungen durch ihre Fluoreszenzeigenschaften eine Online-Messung. Um die Empfindlichkeit und praktischen Grenzen thermo-sensitiver Tracer zu untersuchen, wurden kontrollierte Laborexperimente in einem eigens dafür entwickelten Versuchsaufbau durchgeführt. Dieser besteht aus zwei seriell geschalteten Säulen, die beide mit Sand gefüllt sind und jeweils auf eine eigene Temperatur eingestellt werden können. Somit ist es möglich, verschiedene thermische Einstellungen zu betrachten. Die untersuchten experimentellen Szenarien imitieren größtenteils Feldanwendungen: Durchflussexperimente sowie auch Experimente mit einer Umkehr der Fließrichtung. Darüber hinaus wurde untersucht, ob thermo-sensitive Tracer auch sensitiv gegenüber der Position der Temperaturfront sind. Dabei wurden die Tracer kontinuierlich oder gepulst injiziert. Die Ergebnisse bestätigen die zugrunde liegende Theorie experimentell. Wenn die pH-Abhängigkeit der Hydrolyse bei der Analyse berücksichtigt wird, kann eine Temperaturschätzung mit einer Genauigkeit und Präzision von bis zu 1 K erreicht werden. Die Schätzungen sind von Verweilzeit und gemessenen Konzentrationen unabhängig. Weiterhin lässt sich eine Schätzung über den ausgekühlten Anteil des Systems erhalten. Durch die steuerbaren und definierten Laborbedingungen ist es erstmals möglich, die geforderte Anwendbarkeit von thermo-sensitiven Tracern belastbar nachzuweisen. Des Weiteren wird eine zweite Anwendung hydrolysierender Tracer vorgeschlagen. Beim Lösen von CO2 für „Carbon Capture and Storage“-Anwendungen hängt die Effizienz maßgeblich von der Grenzfläche zwischen CO2 und der Sole in tiefen Reservoiren ab. Somit ist diese Metrik wichtig, um die Effizienz der CO2 Auflösung in Wasser zu bewerten. Die gezielt entwickelten Kinetic-Interface-Senitive-Tracer (KIS-Tracer) nutzen, zusätzlich zur Hydrolyse an der Grenzfläche, die unterschiedlichen Lösungseigenschaften von Tracer und Reaktionsprodukt im entsprechenden Fluid. Somit lassen sich potentiell Aussagen über die Dynamik der Grenzfläche machen. Neben dem grundlegenden Konzept sowie den theoretischen Tracer-Anforderungen wird eine erste Anwendung im Laborexperiment vorgestellt. Diese zeigt das erfolgreiche, zielorientierte Moleküldesign und bietet eine experimentelle Basis für ein makroskopisches numerisches Modell, mit welchem numerische Simulationen verschiedener Testszenarien durchgeführt werden, um das Zusammenspiel von KIS-Tracer und dynamischer Grenzfläche zu untersuchen. Aufgrund der Temperaturabhängigkeit der Reaktionsgeschwindigkeit hydrolysierender Tracer werden in der Regel auch thermische Signale aufgezeichnet. Der letzte Teil prüft die Möglichkeit, Informationen aus den aufgezeichneten Temperaturen zu extrahieren. Für ein idealisiertes Einzelkluftsystem wird eine Reihe von analytischen Lösungen diskutiert. Aus thermischen Injektion-/Entzugsversuchen können damit räumliche und zeitliche Profile abgeleitet werden. Mit der Verwendung von mathematisch effizienten Inversionsverfahren wie der iterativen Laplace-Transformation lassen sich rechentechnisch effiziente Realraum-Lösungen ableiten. Durch die Einführung von drei dimensionslosen Kennzahlen können die berechneten Temperaturprofile auf Bruchbreite oder Wärmetransportrate, wechselnde Injektions-/ Pumpraten und/oder auf in der Nähe beobachtbare räumliche Informationen analysiert werden. Schließlich werden analytische Lösungen als Kernel-Funktionen für nichtlineare Optimierungsalgorithmen vorgestellt. Zusammenfassend bearbeitet die vorliegende Arbeit den Übergang zwischen Tracerauswahl und Traceranwendung. Die Ergebnisse helfen Planungs- und Analyseunsicherheiten zu reduzieren. Dies wird bezüglich der Empfindlichkeit gegenüber Temperaturen, Kühlungsanteilen, flüssig/flüssig-Grenzfläche, Kluftbreite und Wärmetransportrate gezeigt. Somit bieten die vorgestellten Tracerkonzepte neue Metriken zur Verbesserung von Reservoirmanagementverfahren. Die experimentellen Ergebnisse und die neuen analytischen Modelle ermöglichen einen tiefen Einblick in die kollektive Rolle der Parameter, welche die Hydrolyse und den Wärmetransport in Georeservoiren kontrollieren.