Academic literature on the topic 'Low enthalpy geothermic'

The development of district heating systems results in a search for alternative heat sources. One of these is low-enthalpy geothermic energy, more available than traditional geothermal energy. However, utilization of these resources is difficult, due to the low quality of the produced heat. To utilize them, the heat pump system can be used. Such a system was designed for this case study of a city in a region of the Polish Lowlands. The data necessary for the design came from the project of the borehole and operational parameters of the existing heating plant. Four heat pump-cycle designs were proposed, modeled, and simulated using Ebsilon software. Afterward, the designs were optimized to achieve maximum coefficient of performance (COP) value. As a result of the simulation, the efficiency of each design was determined and the seasonal COP value was calculated with the annual measured heat demand of the plant. The system based on the cascade design proved the most efficient, with a seasonal COP of 7.19. The seasonal COP for the remaining basic, subcooling, and regenerator variants was 5.61, 3.73, and 5.60, respectively. The annual heat production of the designed system (22,196 MWh) was calculated based on the thermal power of the designed system and historical demand data. This paper presents a simulation methodology for assessment of the efficiency and feasibility of a heat pump system in district heating.

Geothermal energy is a stable energy, stored underground and not influenced by the geographical, seasonal weather and the change of day and night. Medium-enthalpy and low-enthalpy geothermal energy are distributed in many areas of China, having a broad prospect for development. Taking water resources heat pump (WSHP) engineering in Tianqiao District as an example, medium-enthalpy and low-enthalpy geothermal energy is combined with the technology of aquifer thermal energy storage (ATES), providing cold energy in summer and warm energy in winter for the buildings. On the base of analysis of hydrogeological conditions in Tianqiao District, the temperature field of energy storage aquifers is numerically analyzed in the period of heating and cooling. The results show that the energy storage well can meet the requirement of heating and cooling conditions. The system of WSHP greatly utilizes medium-enthalpy and low-enthalpy geothermal energy, making the running costs economical.

Abstract In Italy 40% of total energy consumption is destined for buildings. To reduce energy consumption and consequently achieve a reduction in carbon dioxide emissions, it is necessary to design well and build better. The technologies that make it possible to increase the energy saving of buildings for civil use are linked to three main aspects: envelope, insulation, and air conditioning; high efficiency systems, integrated building-plant design, use of appliances and lighting with low energy consumption, use of energy from renewable sources; building automation. In this work, the energy demand of a building located in Campania is supplied by a low-enthalpy geothermal plant where the working fluid is a nanofluid. Building thermal loads and performance of the geothermal plant are evaluated by means of TRNSYS®. Borehole heat exchangers design is carried out by means of the ASHRAE procedure. The geothermal system is designed considering the geological characteristics of the site, the characteristics of the geothermal plant and energy conversion system. The performance of the system is evaluated for different nanofluid as working fluid, water-Al2O3, water-CuO and water-SiO2, for several nanoparticle concentrations.

Renewable energies have been the only sources recording a clear increase in total installed capacity, setting a record in new power capacity in 2020, despite the pandemic. The European Union Green Deal represents a strategy towards a sustainable economic model. In this framework, land-based geothermics has seen very limited development; however, offshore geothermics is almost completely absent in the discussion on energy source alternatives, even though it represents a real challenge for energy transition, including the production of green hydrogen. This article discusses an excursus on the activities carried out on offshore geothermal areas worldwide. We focused on the energy potential capacity of the Marsili volcanic seamount located over the bathial plain of the Tyrrhenian Basin, describing the detailed geological, geochemical, and geophysical investigations that have been carried out on that seamount since the 2000s. All the collected data have shown evidence supporting the existence of an exploitable geothermal system in the Marsili seamount consisting of a reservoir of supercritical geothermal fluids of about 100 km3. We discuss and evaluate the actual consistence of the impacts associated with the occurrence of potential risks. We also describe the necessary further steps towards the pilot well. An important breakthrough in the short-medium term that allows for an exit from the predominance of fossil sources may come from the development of energy production derived from offshore high-enthalpy geothermal fields, especially in areas such as the Southern Tyrrhenian Sea. There is a natural clear predisposition for its exploitation combined with a low ecological footprint, which is the target objective of international agreements in the context of a blue economy strategy.

In order to face the growing energy demands, renewable energy sources can provide an alternative to fossil fuels. Thus, low-enthalpy geothermal plants may play a fundamental role in those areas—such as the Province of Viterbo—where shallow groundwater basins occur and conventional geothermal plants cannot be developed. This may lead to being fuelled by locally available sources. The aim of the present paper is to exploit the heat coming from a low-enthalpy geothermal system. The experimental plant consists in a down-hole heat exchanger for civil purposes and can supply thermal needs by district heating. An implementation in MATLAB environment is provided in order to develop a mathematical model. As a consequence, the amount of withdrawable heat can be successfully calculated.

Low enthalpy geothermal resources located within deep Permian and post-Permian sedimentary basins across the UK are estimated to contain at least 300 EJ (x1018 J) of heat, sufficient if fully developed to supply all heating needs in the UK for the next century. The geothermal heat estimate is based on data held within the Geothermal Catalogue (Busby, 2010). A source of deep well data not included in the Geothermal Catalogue is held by the oil and gas industry; access to this data has allowed new geothermal research to be undertaken to re-evaluate and constrain an existing geothermal resource (the Cheshire Basin), and to evaluate a previously un-quantified resource (the East Midlands). These areas were determined based on the availability of oil and gas well data. Data relating to the East Midlands indicate the total available extractable heat from produced oil and co-produced water located in Carboniferous sediments totals 2.64 MWt. In the Welton Field water from non-oil bearing horizons are factored in; the extractable heat increases from 0.91 MWt to 1.6 MWt. The Cheshire Basin uses the offshore East Irish Sea Basin as an analogue to better constrain the aquifer properties of the Triassic Sherwood Sandstone Group (SSG) and Permian Collyhurst Sandstone Group (CS). It also assesses the connectivity of these Groups across the basin. The Helsby Sandstone Formation (part of the SSG) will likely exhibit a minimum transmissivity of 4.26 D m alone. Data for the CS were inconclusive due to diverging porosity trends between the basins; transmissivity could be on average 0.13 D m or 3.85 D m with resulting flow rates of 47.7 m3 d-1 or 1431 m3 d-1. Factoring in reservoir stimulation is deemed necessary if the CS is to be targeted. The connectivity of the basin is restricted by large N-S orientated largely cemented faults, restricting flow in an E W orientation. In addition the connectivity is further affected by facies heterogeneity and diagenesis; this increases tortuosity that may be advantageous in a geothermal context. The work is pertinent given the UK’s commitment to the Kyoto Protocol and Renewable Energy Directive. Geothermal technologies are low CO2 emitters, are non-intermittent, unobtrusive, do not attract large emission-based taxes, have long (~25 year) lifespans and have minimal post-use clean up costs. The uptake of geothermal resource within the UK still remains low, however, indicating barriers to uptake exist. Technical barriers (i.e. those relating to drilling of the well, geology, flow rates and temperature) are not limiting uptake. Non-technical barriers relating to lack of risk insurance schemes and longer payback times owing to the relative value of hot water versus petroleum are identified as restricting factors to the uptake of geothermal resources. Geothermal energy development in the UK is still in its infancy and work such as this only strengthens the case for investment. The potential for geothermal resource exploitation to offset the conventional energy consumed to produce heat is sizeable; no other renewable technology has the capacity to deliver heat that low enthalpy geothermal offers.

The Danish subsurface provides a large potential for the use of low-enthalpy geothermal heat and, thereby, to change the national district heating structure by providing a base load power to the system. In the past decade, new exploration and research campaigns were performed to remove geological, technical and commercial obstacles for a significant use of these geothermal resources. One of the obstacles is the lack of knowledge on the thermophysical rock properties. Subsurface thermal conditions as well as the production capacity and lifecycle of geothermal district heating plants largely depend, among other, on these properties. For the Danish Basin only few published data sets are available and mostly limited to thermal conductivity. Values of thermal diffusivity and specific heat capacity are mostly unknown. In order to overcome this gap, new laboratory measurements were conducted. Thermal conductivity and thermal diffusivity were measured on drill cores sections, while specific heat capacity was calculated based on these values and on rock density. Geological targets for the study are Mesozoic reservoir sandstones (Gassum Fm., Frederikshavn Fm., Haldager Sand Fm.), but also mud-/claystones and limestones of seal rocks (Fjerritslev Fm., Vedsted Fm.). The rock suite of 43 specimens studied was sampled in six wells. The measurements are performed under dry and saturated conditions using the optical scanning method. Furthermore, the values of conductivity and thermal diffusivity of the matrix were obtained by geometric mean averaging. Therefore, the ranges of characteristic values for each lithology were identified and a qualitative survey on the mineralogical composition of the samples on the basis of the matrix data was assembled. Further observations on the behaviour of thermal diffusivity and the relative application of the geometric mean model are also provided. This study was possible thanks to the "GEOTHERM" project, funded by the Innovation Fund Denmark.

South Africa generates more than 90 percent of its total energy capacity through non-renewable sources. With coal forming the predominant energy source, South Africa became the leading carbon emissive nation in Africa, emitting 450 million tonnes of CO2 in 2011. In an international effort to restrict global average temperature rise to 2° C above the average prior the industrial revolution, the Kyoto Protocol has been extended for another 8-year commitment period. This is complementary to an expected resolution of a new legally binding climate change policy in 2015. This policy will aim to introduce financial penalties for nations failing to meet ascribed GHG emission targets by 2020. In an attempt to meet these climate change resolutions South Africa will research and develop cleaner, alternative forms of energy, including hydro, wind, and biomass forms of renewable energy, in addition to designating stringent building regulations for the Incorporation of solar energy. These measures form part of an Integrated evelopment Plan that aims to generate a target of 10,000 GWh of renewable energy in 2013. South Africa is also investigating the possibilities of extracting its shale gas reserves and implementing it as a major energy source. This energy mix has given little attention to geothermal energy. The reasons for this omission appears to be the lack of active volcanism and previous research that suggests South Africa, largely underlain by the Kaapvaal Craton, has a relatively low heat Flow profile, deemed insufficient for harnessing geothermal energy.

The ground source resources are becoming more and more popular and now the ground source heat pumps are frequently used for heating and cooling different types of buildings. This thesis aims at giving a contribution in the development of the thermal modelling of borehole heat storage systems. Furthermore, its objective is to investigate the possibility of implementing of a GSHP (ground source heat pump) with vertical boreholes, in order to deliver the heating and cooling demand for a passive house and to emphasize some certain advantages of this equipment even in the case of a small building (e.g. residential house). A case study is presented to a suitable modelling tool for the estimation of the thermal behaviour of these systems GSHP by combining the outcome from different modelling programs. In order to do that, a very efficient residential solar house (EFden House – a passive residential single-family house, which was projected and built in Bucharest with academic purposes) is being analysed. The numerical results are produced using the software DesignBuilder, EED (Earth Energy Designer) and a sizing method for the length of the boreholes (ASHRAE method). The idea of using 2 different modelling programs and another sizing method for the borehole heat exchanger design (ASHRAE method) is to make sure that all the calculations and results are valid and reliable when analysing such a system theoretically (in the first phases of implementing a project), before performing a geotechnical study or a thermal response test in order to assess the feasibility of such a project beforehand. The results highlight that the length of the borehole, which is the main design parameter and also a good index in estimating the cost of the system, is directly influenced by the other fundamental variables like thermal conductivity of the grout, of the soil and the heat carrier fluid. Also, some correlations between these parameters and the COP (coefficient of performance) of the system were made. The idea of sizing the length of boreholes using two different methods shows the reliability of the modelling tool. The results showed a difference of only 2.5%.  Moreover, the length of borehole is very important as it was calculated that can trigger a difference in electricity consumption of the GSHP up to 28%. It also showed the fact that the design of the whole system can be done beforehand just using modelling tools, without performing tests in-situ. The method aims at being considered as an efficient tool to estimate the length of the borehole of a GSHP system using several modelling tools.

The presentation was made via Skype due to the programme being online based

The geothermal heat pump systems have been developed in Italy only during the last few years and today only some regions are investing in this field. In particular, the Tuscany Region and the Autonomus Bolzano Province have promoted the study of these systems with the objective of being able to promote and to disclose in the time this technology. A fundamental aspect for a oculata planning and a greater knowledge of the real predisposition of the territory to the installation is sure the acquaintance of the specification of the geological, geophysical, geotechnical and hidrogeological systems and the parameters that enter at stake. The fundamental parameter in a position to discriminating from a point of view not only economic but also of real thermal yield is the thermal conductivity that the determinated site is able to offer. This research examines the essential elements that they characterize a system of geothermal heat pump system. It has been to such respect important to study at first the various type of systems from a technical-engineering point of view that of principle operation. In a second phase, the parameters were characterized to consider in phase of thermal characterization, therefore the study of the heat conductivity, the transmission of heat between probe and land, the thermal stability and the thermal behavior of the ground. In particular, regarding the study of the heat conductivity, in the Capitol 3 are given the tools used for the acquisition of such parameter through investigations in the laboratory and in situ. Successively the normatives elements that regulate the phases of authorization were characterized and analyzed, afterwards planning and installation of the heat pumps systems in the various international and national contexts were considered. A panoramic pre-emptive of the normative picture of the Nations and Regions was drawn to the vanguard in the field of geothermal energy to low and the lowest entalpy. This was dictated by the requirement to define the problematic ones met from the agencies that have legislated in matter and to put of in evidence virtues and criticality. The checks carried out both in terms of legal and procedural provided an inspiration for the creation of authorization processes and procedures for the installation of various types of geothermal heat pump systems in various geological contexts, in order to assess the possible impacts that these systems can cause on the environmental matrices. Central part of the research project is the study of the heat conductivity, parameter key for the development of a useful cartography in this field. It was decided to perform a literature search of that parameter, in order to process and then compare the data of thermal conductivity obtained from detailed investigation carried out in a pilot site and found through the stratigraphy. In fact, nowadays the available data measured on lithologies of the Italian territory are few and hard to find. The literature research has allowed later to thermally classify the lithostratigraphic units of the geological legend of Sardinia Region, in scale 1:10000, one of the few regions to boast of an updated geological territorial Continuum. The performed research is based on the possibility of drawing up maps of the thermal conductivity from the investigation and trying different methods, ultimately, to compare the two approaches. The first method concerned a detailed investigation of the pilot site located in proximity of Lago Baratz (Municipality of Sassari) through a geological and hidrogeological framework, a pedologic survey and at last, investigations of geoelectrical type. The detailed study has afforded to frame the site potentially interesting to the installation of a system being afforded to characterize from a thermal point of view the area. Therefore, it has been possible to calculate the value of thermal yield for 1800 – 2400 hours of operation of the system in modality cooling and heating. By means of the second method of calculation, it was considered appropriate to disclose a test personally conducted in the territory of the Arezzo Province. Thus, it is reported below an example of processing of the data of thermal conductivity from the stratigraphic information. Giving the high number of information (about 12566 stratigraphic data points), it was decided to perform a first test in order to verify and consolidate the processing procedure. In the Chapter 7 all the passages executed for the elaboration of the thermal conductivity data from the stratigraphic information for the provincial territory are illustrated. Three maps for the depths of interest of 30, 60 and 100 meters Were elaborated. Successively the respective papers of the errors were calculated, allowing to divide the province territory in areas for which it can be identified different planes of address to be followed in the process of thermal characterization. The last chapter contains a possible synthesis of a procedural iter initially for defining the parts that enter as stake in phase of realization of a system. They will follow some detailed lists reported to the criteria to follow, in sensitive areas, for the study and the control from a thermal point of view, of a potentially apt site to the installation of a system The entire research aims to set an example as well as the application of geological information at a scale of detail, the stratigraphic information and spread knowledge of the parameters involved can be combined to create thematic maps useful for public authorities and citizens.

This study presents an investigation of the concept of harvesting geothermal energy that remains in heavy oil reservoirs after abandonment when steamflooding is no longer economics. Substantial heat that has accumulated within reservoir rock and its vicinity can be extracted by circulating water relatively colder than reservoir temperature. We use compositional reservoir simulation coupled with a semianalytical equation of the wellbore heat loss approximation to estimate surface heat recovery. Additionally, sensitivity analyses provide understanding of the effect of various parameters on heat recovery in the artificial geothermal resources. Using the current state-of-art technology, the cumulative electrical power generated from heat recovered is about 246 MWhr accounting for 90percent downtime. Characteristics of heat storage within the reservoir rock were identified. The factors with the largest impact on the energy recovery during the water injection phase are the duration of the steamflood (which dictates the amount of heat accumulated in the reservoir) and the original reservoir energy in place. Outlet reservoir-fluid temperatures are used to approximate heat loss along the wellbore and estimate surface fluid temperature using the semianalytical approaches. For the injection well with insulation, results indicate that differences in fluid temperature between surface and bottomhole are negligible. However, for the conventional production well, heat loss is estimated around 13 percent resulting in the average surface temperature of 72 degrees C. Producing heat can be used in two applications: direct uses and electricity generation. For the electricity generation application that is used in the economic consideration, the net electrical power generated by this arrival fluid temperature is approximately 3 kW per one producing pattern using Ener-G-Rotors.

L’energia geotermica a bassa entalpia è una risorsa rinnovabile che è ancora poco sviluppata al giorno d'oggi rispetto al suo potenziale sviluppo in Italia e in tutto il Mondo. La maggior parte delle sue possibilità di impiego sono già state studiate, come ad esempio: riscaldamento e il raffreddamento degli edifici privati e pubblici, sbrinamento di strade, raffreddamento di processi industriali, sistemi di essiccamento delle di produzioni agroalimentari, desalinizzazione. Due dei principali limiti legati allo sviluppo del sistema geotermico a bassa entalpia riguardano i costi iniziali, la poca conoscenza che l’opinione pubblica ha su questo argomento e cosa potrebbe provocare nel tempo la variazione termica su acqua e suo-lo dovuta allo sfruttamento di questi sistemi geotermici. Al fine di ottimizzare l'efficienza degli impianti che usano le acque sotterranee come risorsa geotermica, il flusso e la dinamica di trasporto di calore in falde acquifere hanno bisogno di essere ben caratterizzati. La mancata conoscenza riguardo le dinamiche di trasporto di calore di acquiferi fratturati ma anche porosi porta a sovra-dimensionare gli impianti aumentando ulteriormente i costi iniziali. La risorsa geotermica a bassa entalpia, tuttavia, è sempre utilizzabile e facilmente disponibile. Le sperimentazioni effettuate in questo percorso di ricerca sono state sviluppate principalmente nell’ottica di poter analizzare le potenzialità e per ottimizzare sistemi geotermici aperti a bassa entalpia che operano all'interno dello stesso pozzo geotermico, quindi sistemi cortocircuitati. Questo tipo di sistema è stato pensato soprattutto per diminuire l'impatto ambientale dovuto dall'iniezione di acqua a temperatura maggiore rispetto alla temperatura di presa. In questo modo, infatti, è possibile con-tenere le variazioni termiche all'interno di una stessa area di interesse. Nel corso di questi tre anni di dottorato sono stati condotti diversi esperimenti a scala di banco con i quali sono stati prodotti dei lavori pubblicati su riviste scientifiche internazionali. Gli esperimenti si sono divisi in due macro categorie accumunate dall’unico obiettivo di comprendere le dinamiche di trasporto di calore: studio di calore in mezzi fratturati e studio di calore in mezzi porosi a diversa granulometria. Il primo test ha riguardato in particolare lo studio del trasporto di calore in mezzi fratturati. Pertanto si è costruito un prototipo a scala di banco presso il laboratorio di geo-ingegneria ambientale del Politecnico di Bari. Su questo prototipo sono stati eseguiti diversi test in particolare è stato analizzato il comportamento del trasporto di calore prima in singola frattura e successivamente in un network di fratture. Il trasporto di calore è stato così confrontato con il trasporto di massa. Sono state ottenute delle curve di risposta termica (BTCs) che sono state modellate con l' Esplicit Network Model (ENM), che si basa su un adattamento della soluzione di un Tang per il trasporto dei soluti in una singola frattura semi-infinita incorporata in una matrice porosa. La stima del time moment analisys, tailing e altri parametri adimensionali hanno per-messo di comprendere meglio le dinamiche di trasporto di calore e l'efficienza di scambio termico tra le fratture e matrice. I risultati sono stati confrontati con i prece-denti studi sperimentali in materia di trasporto di soluti. Successivamente, sono state eseguite delle prove in sito presso la piattaforma sperimentale dell’università di LaSalle di Beauvais (Francia) con la quale per due anni c’è stato un rapporto di collaborazione con l’obiettivo di studiare il trasporto di calore in mezzi gessosi fratturati. Sono state eseguite delle prove a gradiente naturale utilizzando il calore come tracciante. Successivamente ci si è concentrati sullo studio delle dinamiche del trasporto di calore in mezzi porosi. E' stato creato un altro prototipo per studiare il trasporto di calore in mezzi porosi. Sono stati condotti diversi test sul prototipo a scala di banco riempito con materiale avente diversa granulometria. Gli esperimenti consistevano nell'iniettare portate d'acqua calda a temperatura nota in corrispondenza di termocoppie posizionate lungo una colonna mezzo poroso. Sono state così ottenute delle curve di risposta termica (BTCs). Questo studio ha permesso di studiare le criticità riguardanti il trasporto del calore in mezzi porosi al variare della granulometria, ed ottenere dei risultati in merito al rapporto tra la velocità di flusso e la dispersione termica e la validità dell’equilibrio termico e del non equilibrio termico per descrivere il comportamento tra fase fluida e solida al variare della granulometria, che hanno permesso, confrontando i dati ottenuti nei test precedenti con il fratturato di ottenere dei risultati importanti. Dal confronto di questi studi, è emerso che la superficie specifica del mezzo gioca un ruolo estremamente importante nelle dinamiche di trasporto di calore. Al variare della superficie specifica, il sistema geo-termico (acquifero) riesce a trattenere più o meno calore. In particolare, gli studi effettuati, dimostrano che un acquifero caratterizzato da un mezzo con alta superficie specifica, a parità di portata, si presta meglio a trattenere calore, pertanto un sistema a bassa superficie specifica si presta meglio ad accumulare calore, ad immagazzinarlo e ad essere quindi sfruttato come accumulatore di calore. Al contrario, un sistema caratterizzato da bassa superficie specifica è maggiormente indicato per immettere calore proveniente da un sistema geotermico, in quanto tende a cedere molto prima il calore rispetto ad un sistema ad elevata superficie specifica. Da questo emerge un altro fattore importante che riguarda un sistema fratturato. Il valore della dispersione termica teorica risulta molto inferiore rispetto al valore della dispersione osservata dai test di laboratorio. Infatti la dispersione termica per un sistema fratturato gioca un ruolo molto importante, è molto significativa per l’analisi delle dinamiche del trasporto di calore e non è trascurabile. E’ emerso inoltre che anche l’effetto channeling gioca un ruolo importante così come l'interazione frattura matrice. Nel caso di un sistema fratturato, infatti, l'effetto channeling nelle curve di risposta termica (BTCs) e nei diversi parametri analizzati è molto evidente. La lunga coda e il picco anticipato di-pendono dell'effetto channeling e dall’ interazione matrice-frattura. Dall’analisi di questi studi emerge che la superficie specifica del mezzo gioca un ruolo estremamente importante. Infatti variando la superficie specifica, le formazioni caratteristiche di un acquifero tenderebbero ad immagazzinare più o meno calore. Mezzi con bassa superficie specifica del mezzo, a parità di portata, proprietà idrauliche e termiche, presentano elevata capacità di immagazzinare calore rispetto a formazioni caratterizzate da un’alta superficie specifica che presentano migliori proprietà di dissipare calore. Se le fratture hanno un'alta densità e sono ben collegate, tale che i blocchi matriciali sono piccoli, la condizione ottimali per lo scambio termico non è raggiunta in quanto i blocchi della matrice hanno una limitata capacità di accumulare calore. Pertanto, sembrerebbe che le formazioni con matrice porosa a grandi blocchi siano le formazioni geologiche ottimali da sfruttare per lo sviluppo di energia geotermica. La stima della effettiva coefficiente di conducibilità termica media dimostra che le rocce con alta densità di fratturazione non si prestano ad immagazzinare l'energia termica, poiché le fratture sono circondate da una matrice con più limitate capacità di diffusione dando luogo ad un aumento della resistenza termica. Lo studio potrebbe contribuire a migliorare l'efficienza e l’ottimizzazione dei sistemi industriali e ambientali, e può permettere una migliore comprensione dei processi geologici che comportano un trasferimento di calore nel sottosuolo. Gli sviluppi futuri di questo studio si baseranno su ulteriori indagini ed esperimenti volti ad comprendere quantitativamente come l’interazione frattura-matrice può influenzare l'efficienza di uno stoccaggio e i fenomeni di dissipazione di energia termica nelle falde acquifere. Questo risultato potrebbe essere ottenuto attraverso esperimenti di laboratorio che utilizzino formazioni differenti con diversa densità di frattura e porosità della matrice. Sarebbe interessante procedere con lo studio del trasporto di calore al variare dello spessore, rugosità e altri parametri chiave delle fratture e proseguire con studiare nuovi sistemi geotermici che permettano di contenere l'impatto ambientale sull'acqua e sul suolo di sistemi geotermici a bassa entalpia, e allo stesso tempo di diminuire i costi ottenendo un'ottimizzazione del sistema.
Low enthalpy geothermal energy is a renewable resource that is still underexploited nowadays, in relation to its potential for development in the society worldwide. Most of its applicability have already been investigated, such as: heating and cooling of private and public buildings, roads defrost, cooling of industrial processes, food drying systems, desalination. Some of the main limitations related to the development of low-enthalpy geothermal system are represented by the initial costs, the lack of knowledge that the public has in this topic and the negative effect that a geothermal system could cause during time on environmental factors. The lack of knowledge regarding the heat transfer dynamics of fractured aquifers and porous, leads to oversizing the systems by further increasing the initial costs. In order to optimize the efficiency of the systems that use groundwater as geother-mal resource, the flow and heat transfer in dynamic aquifers need to be well characterized. The low enthalpy geothermal resource, however, is always usable and easily availa-ble. Experiments carried out in this research have been developed mainly in order to be able to analyze the potential and to optimize short-circuited low-enthalpy geothermal systems. This type of system has been designed especially to decrease the environ-mental impact caused by the injection of water at a temperature higher than the ground water temperature. In this way, in fact, it is possible to reduce thermal variations within a same area of interest. The tests conducted in these three years therefore aim to characterize the dynamics of heat transport in porous and fractured aquifers to optimize the efficiency of circuited low enthalpy geothermal systems. Therefore has been built a prototype at the bench scale at environmental geo engineering laboratory of the Polytechnic of Bari. On this prototype several test have been performed to analyse the dynamics of heat transport in a single fracture and in a fracture networks. The heat transport has been compared with the mass transport. During these three years of PhD study, some experiments have been conducted which have enabled the production of some papers, published in international scientific journals. The dynamics of heat transfer have been studied in fractured media and in porous media at different grain sizes. First of all the heat transport in fractured media was studied, and compared this with the mass. In order to model the obtained thermal breakthrough curves, the Explicit Network Model (ENM) has been used, which is based on an adaptation of a Tang’s solution for the transport of the solutes in a semi-infinite single fracture embedded in a porous matrix. Parameter estimation, time moment analysis, tailing character and other dimension-less parameters have permitted to better understand the dynamics of heat transport and the efficiency of heat exchange between the fractures and matrix. The results have been compared with the previous experimental studies on solute transport. Subsequently, some tests in situ have been performed on fractured chalky, at the experimental platform of Polytechnic of La Salle Beauvais. A natural gradient test has been carried out using hot water as a tracer. Subsequently, have been analyzed in the laboratory the dynamics of the heat transport in porous media, so has been cre-ated another prototype at bench-scale. Several tests are conducted in laboratory on prototype, at bench-scale, filled with different grain size materials. The experiments consisted in injecting hot water flow at known temperatures in a porous medium column. The thermal response curves (BTCs) have been obtained. This study has permitted to investigate the critical issues regarding the heat transport in porous media to vary the grain size, and obtain the results regarding the relationship between the flow rate and the heat loss and the heat balance and validity of the non-thermal equilibrium, to describe the behaviour of fluid and solid phase varying the particle size, which allowed, by comparing the data obtained in previous tests with fractured, to obtain important results. From these studies it was found that the specific surface of the medium plays an extremely important role. By varying the specific surface, the geothermal system (aquifer) seems to retain more or less heat. It would seem that aquifer characterized by an high specific surface, at the same flow rate, is better suited to retain heat, therefore a low specific surface system lends itself better to accumulate heat, to store it and to be therefore exploited as a heat accumulator. On the contrary, a system characterized by low specific surface area is more suited to enter heat from a geothermal system, as it tends to dissipate earlier heat respect to a high specific surface system. From this emerges another important factor affecting a fractured system. Furthermore, the theoretical thermal dispersion is much lower than the dispersion observed by laboratory tests. In fact, the thermal dispersion for a fractured system plays a very important role, is very significant as regards the behaviour of the between extruded heat and is not negligible. The channelling effect plays an important role as well as the fracture matrix interaction. In the case of a fractured system, in fact, the channeling effect in the thermal BTCS and in the different parameters analyzed is very clear. The long tail and the anticipated peak depend channelling effect and matrix-fracture interaction. This study show that the specific surface of the medium plays an extremely important role. By varying the specific surface area, the subsurface reservoir formations is able to retain more or less heat due to variation of thermal dispersion. From the present studies, have been found, in fact, that an subsurface reservoir formations characterized by a low specific surface, at the same flow rate, at the same hydraulic and thermal properties, presents high capability to store heat respect to the subsurface reservoir formations characterized by a high specific surface system that has better properties to dissipate heat In fact, if the fractures in the reservoir have a high density and are well connected, such that the matrix blocks are small, the optimal conditions for thermal exchange are not reached as the matrix blocks have a limited capability to store heat. Therefore, subsurface reservoir formations with large porous matrix blocks will be the optimal geological formations to be exploited for ge-othermal power development. In fact, if the fractures in the reservoir have a high density and are well connected, such that the matrix blocks are small, the optimal conditions for thermal exchange are not reached as the matrix blocks have a limited capability to store heat. The estimation of the average effective thermal conductivity coefficient shows that it is not efficient to store thermal energy in rocks with high fracture density because the fractures are surrounded by a matrix with more limited capacity for diffusion giving rise to an increase in solid thermal resistance. On the other hand, isolated permeable fractures will tend to lead to the more distribution of heat throughout the matrix. The study could help to improve the efficiency and optimization of industrial and en-vironmental systems, and may provide a better understanding of geological processes involving transient heat transfer in the subsurface. Future developments of the current study will be carrying out investigations and experiments aimed at further deepening the quantitative understanding of how fracture arrangement and matrix interactions affect the efficiency of storing and dissipation thermal energy in aquifers. This result could be achieved by means of using different formations with different fracture density and matrix porosity. Results from this study are very interesting for further development of existing geo-thermal technologies. It would be interesting to proceed with the study of heat transport to vary the thickness, roughness and other key parameters of fractures and continue to study new geothermal systems that allow, starting from the experi-mental knowledge, to contain greater the environmental impact on water and soil of low enthalpy geothermal systems, and at the same time allow to reduce the costs while achieving an optimization of the system.

Abstract The electrical submersible pump (ESP) is an essential and critical component in most low-enthalpy geothermal wells where high volumes of hot (up to 120°C) and harsh geothermal brine is required to be transported to the surface. Despite a great deal of knowledge and experience in the design and operation of ESP in the petroleum and water sector, reliability of geothermal ESPs requires further improvement. Frequent failures have been observed that resulted from sub-optimum design, installation and operation of these systems which made the lifetime of them shorter than the expected 5-7 years. In this paper we summarize the typical conditions in low-enthalpy geothermal systems (specifically in the Netherlands) and several observed reliability challenges. Lastly, we will discuss the gaps between the petroleum, water and geothermal practices and identify a list of R&D opportunities to better understand the geothermal ESP failures and improve ESP reliability. Testing ESPs in realistic geothermal conditions and a proper monitoring of the well-ESP system is crucial to improve the reliability of existing ESP designs and can enable the development of new geothermal ESP system designs.

Geothermal energy is one of the no fossil energy sources that has been utilized mainly for electricity generation, by using the so-called high enthalpy geothermal resource. Nevertheless, low and medium enthalpy geothermal resources are most abundant, but utilized in less extension due mainly to technological barriers or the thermal match between temperature of energy resources and the technology requirements. This work presents the analysis of alternatives for integrating a multiproduct system, producing sequentially electricity, ice and useful heating. For the purpose, the cascade utilization concept is considered for geothermal energy, utilizing low and medium enthalpy resources. To carry out the analysis, it is assumed availability of geothermal hot water with different temperatures typical of already drilled geothermal wells or studied geothermal reservoirs in Mexico. In order to produce electricity, ice and heating for further use (dehydration process or greenhouse heat supply), three cascade levels are proposed to operate sequentially and simultaneously. For electricity generation Organic Rankine Cycles are considered, and for ice production, thermally activated technologies are the best candidates. If necessary, supplementary heat is provided as a mean of geothermal energy upgrade; among the technologies to integrate are parabolic trough collectors, linear Fresnel collectors and biomass boiler. Particularly, with regard to Organic Rankine Cycles, are considered the ones that works with geothermal hot water in the range of 90 °C to 125 °C with rated power output between 25 kWe to 250 kWe. For ice production, two type of machines are under study, i.e. single-effect absorption machines with coefficient of performance around 0.6, and half-effect absorption machines with a value around 0.3 for the coefficient of performance. Absorption machines can be activated thermally with geothermal hot water with temperature in the range of 70 °C to 90 °C. Afterwards, a number of alternatives are proposed to integrate the multiproduct system, which are analyzed and compared both from the energy and economic point of view, obtaining in this way the main energy interactions of the systems, including electricity produced, amount of ice produced and heat availability. In the model, economic indicators are evaluated, obtaining for each alternative the capital cost, simple payback and net present value. Results shows quantitatively that cascade use of geothermal energy is a viable concept to increase the use of low and medium enthalpy geothermal resources with increase of energy performance and improvement of economical profit.