Low Enthalpy Geothermal Field Research Articles

Coupled Modeling of the Surface Pipeline Network in a Low-Enthalpy Geothermal Field

This paper addresses the often overlooked, yet critical, aspect of designing and optimizing the surface pipeline network for the transportation of geothermal fluids from the wellheads to the delivery point, such as greenhouses, food drying plants, or fish farming units. While research on the geothermal industry predominately focuses on the reservoir and well engineering aspects of exploitation, insufficient attention has been given to the design of the pipeline network, leading to improper design and significant, yet avoidable, energy losses. Thus, this paper presents a comprehensive methodology for modeling and simulating geothermal fluid flow within the pipeline network by fully considering all hydraulic (friction, viscous flow, and gravity effects) and thermal (open air and underground pipeline heat loss) phenomena. These two aspects are handled simultaneously by setting up and solving the coupled set of the governing (differential) equations. We also demonstrate the difficulties that arise when attempting the solution of the mathematical problem, such as potential instability or lack of convergence. Finally, a fully detailed study of the real-world geothermal production system is presented utilizing the developed methodology to optimize the design and operation conditions of the system. By integrating debottlenecking strategies into the analysis, this approach not only maximizes power output, but also identifies and mitigates constraints within the system, ensuring efficient operation and performance increase.

Geothermal groundwater study and its energetic potential assessment in Abu Gharadig Basin, North Western Desert, Egypt

The Abu Gharadig Basin (AGB) is one of Egypt's main oil-producing basins, characterized by a range of tectonic structures generated by intense extension and the deposition of a thick sedimentary sequence, making it an ideal location for geothermal energy research. In this study, seven groundwater samples were collected from wells drilled in the AGB to conduct hydrochemical and isotopic analyses. The results indicate that the region's groundwater is dominated by Na+ cations and Cl− anions, which originate from precipitation and runoff. The application of cation geothermometers reveals that all the groundwater samples are in partial equilibrium with the host rock and may also be from mixed sources. The temperature of the deep geothermal reservoir can be estimated using cation geothermometers. The calculated reservoir temperature range deduced from Na–K–Ca geothermometry is 127–184 °C, with an average of 157 °C. The quantities of geothermal power stored in the vicinity of the AGB low-enthalpy geothermal field over the next 25 and 50 years were estimated using stochastic Monte Carlo simulations. For a site with a surface area of 1 km2, the geothermal power potential is 14.3 MWe for a 25-year lifespan and 7.16 MWe for a 50-year lifespan.

Hydrochemistry and geothermometry of thermal waters from UAE and their energetic potential assessment

Two main low-enthalpy geothermal fields are present in the UAE: Mubazzarah-Ain Faidha (Al-Ain city) in the Abu Dhabi Emirate and Ain-Khatt in the Ras Al-Khaimah (RAK) Emirate. The chemistry of nineteen waters was analyzed to calculate geothermal reservoir temperatures using cation and silica geothermometers, and to describe the source of recharge of the hot waters from isotopic data. In total, 19 water samples (16 from wells, 2 from springs AF and KT1 and one sea water) were collected and analyzed for major anion and cation concentrations. The isotope and chemical data suggest that the hot waters from Al-Ain (Mubazzarah and Ain Faidha) are almost entirely recharged by rainwater, which originates at higher altitude, heats up through deep water circulation, and travels to the surface through fault structures within the study area. The waters are mainly Na-Cl type, and the discharge temperatures range from 32.5 °C to 49 °C. The Na-K geothermometers predict a geothermal reservoir temperature of 151 °C for the Mubazzarah-Ain Faidha hot waters and 112 °C for the Ain-Khatt hot waters with estimated depth of water penetration of 3.8 km and 2.6 km, respectively. The existing known geothermal resources in the Mubazzarah and Ain Khatt areas can be immediately and sustainably used for low-temperature, direct-use geothermal applications. A stochastic Monte Carlo simulation was performed to estimate the geothermal energy stored in the two main low-enthalpy geothermal fields for 25 years and 50 years. The geothermal electricity potential at Mubazzarah-Ain Faidha is ∼16.5 MWe and ∼8.27 MWe for 25 and 50 years, respectively. The geothermal electricity potential at Ain Khatt is ∼291 kWe and ∼146 kWe for 25 and 50 years, respectively. These preliminary potential assessments are subject to further delineation drilling and availability of field performance data and considered that the geothermal power plant has either a single or multiple ORC systems due to the very low temperature.

A review of geothermal energy status and potentials in Middle-East countries

Geothermal energy production and consumption is one of the world’s top priorities as it ensures sustainable developments via steady yield of renewable energy and helps to reduce atmospheric carbon dioxide (CO2) emissions and air pollution levels. The objective of this study is to critically assess geothermal energy prospects in terms of number of proven geothermal reservoirs, thermal energy capacities, and potential areas of utilization across thirteen Middle East countries (MECs). The findings from this study show that most oil-rich MECs have not adequately explored/exploited their geothermal resources as evidenced by lack of research and exploration activities. It was found that the current geothermal reservoirs/resources across all the MECs are mostly medium (100–150 °C) and low ( 150 °C) enthalpy geothermal fields. For low/depleted oil and gas reserves countries, full exploitation of geothermal energy is deemed as one of the options to meet their energy demands. In order to fully optimize the geothermal energy productions, it is imperative for these countries to employ advanced geothermal energy production technologies (GEPTs). MECs could learn the experiences of Europe and US to develop their own GEPTs including national and regional strategies and policy frameworks to help fully harness these valuable geothermal resources. These targets are possible through research, trainings, and international collaborations.

Fluid geochemistry in a low-enthalpy geothermal field along a sector of southern Apennines chain (Italy)

The chemical and isotopic features of the fluids (water and gases) in the Lucane thermal area (southern Italy) have been investigated in order to verify their origin, water temperature in the geothermal reservoir, and to recognize the main natural processes concerning the water composition during ascent towards the surface. The Lucane geothermal system is placed in the southern sector of the Apennines chains, a seismically active area, close to the southern base of the Mt. Alpi carbonate massif. Along the study area, two main sets of high-angle faults form an almost orthogonal fault system that, as suggested by local structural geology, acts as a preferential pathway for uprising deep fluids. Here, we recognized two different types of waters: (i) cold shallow waters having a meteoritic origin and interacting with carbonate rocks (dolomite and calcite), whose dissolved gases show a dominant atmospheric contribution and (ii) hypothermal waters (average temperature of 21 °C), having a meteoritic origin and interacting with both carbonate rocks and inter-bedded evaporitic deposit. Geochemical data allow estimating a geothermal reservoir temperature between 30 °C and 60 °C, according to silica and Ca/Mg geothermometers, respectively. A heat discharge related to hypothermal groundwater flow between 7.75E+06 and 2.00E+07 J/s was computed. δ18O and δ2Η data allowed recognizing a meteoric origin for hypothermal (hereafter TL) waters, with mean recharge (infiltration) elevations between 1300 and 1700 m a.s.l. These waters are gas-rich (e.g., CO2 and He), which amounts are higher than those in air-saturated water (ASW). Carbon and helium isotope signature in the TL waters indicate their mainly crustal origin and involve a tectonic control on fluid migration through the crust. Furthermore, we observe that the He isotopic signature in gases dissolved in TL waters is stable over time and its monitoring could be a powerful tool to assess the seismogenetic processes since their preparatory phases.

A STUDY OF FIELD GEOTHERMAL POWER POTENTIAL & THERMODYNAMIC CONCEPTS OF PROSPECTIVE BINARY POWER CYCLE BASED GEOTHERMAL POWER PLANT FOR TATAPANI GEOTHERMAL FIELD.

Tatapani Geothermal field is one of the most promising low-enthalpy geothermal fields in central India, located on Son-Narmada lineament in the state of Chhattisgarh, India. The Tatapani geothermal field geological, geo-chemical & reservoir data has been compiled and analysed for evaluating true power potential & better understanding of the field. The low enthalpy geothermal reservoirs can be utilized for power production using Organic Rankine Cycle (ORC) or binary power cycle. Based on previous research works done, the Tatapani geothermal field has been found to be very prospective and has got huge potential for power generation. The binary power cycle has been studied in detail along with thermodynamic concepts. In addition, similar low enthalpy geothermal power plants (conceptual & existing both) have been thoroughly studied in order to understand the concepts and methodology to perform technical feasibility based on thermodynamic and exergy analysis. The literature review covers the previous works done on Tatapani geothermal field including works on other geothermal fields in India along with previous research works for Thermodynamic & Exergy Analysis carried-out for binary geothermal power plants across the world for similar low enthalpy prospects. The methods of performing thermodynamic and exergy analysis for a potential geothermal power plant has been studied and compared. Exergy analysis highlights the areas of primary exergy destruction at various plant components and can be illustrated in the form of exergy flow diagram. The loss of exergy indicates the potential reasons for the inefficiencies within a process and exergic efficiency as conversion of input heat energy from the brine in to useful work output. The exergic efficiencies can be calculated for each component along with exergy destruction. The detailed study has been conducted in order to gather the knowledge regarding conducting the feasibility of setting up binary geothermal power plant at Tatapani from technical point of view using thermodynamic concepts.

Thermodynamic Analysis on the Performance of a Low-Enthalpy Geothermal Field Using a CO 2 Supercritical Binary Cycle

The exploitation of geothermal energy can play a significant role for providing clean and renewable energy, especially when environmentally-friendly working fluids are used for power production. Along these lines, in the present work a thorough analysis is attempted on the thermodynamic performance and the power production potential of a binary cycle, using supercritical carbon dioxide (sCO2) as working fluid, for the exploitation of a low-enthalpy geothermal field, located in Sidirokastron, Greece. As regards the associated analysis, simplified thermodynamic models of the sCO2 cycle were developed, attempting to incorporate the binary-cycle main components performance characteristics, based on the literature-available data of similar applications. For further improvement of the thermodynamic cycle performance, the use of preheating of the working fluid after the condenser, with the use of solar power, was also considered. The effect of cycle heat-addition pressure and heat-rejection temperature conditions were assessed through parametric studies, taking into consideration the annual regional variations. Furthermore, the effect of the technology level of the critical cycle components, such as the heat exchangers, on the thermodynamic cycle performance was considered. The results were compared to similar, low-enthalpy configurations described in literature. The aforementioned analysis clearly reveals the effect of cycle-operating conditions on the thermodynamic performance of the binary cycle and the high potential of using sCO2 as working fluid, for the exploitation of low-enthalpy geothermal fields, in the pursue of an environmentally-friendly power production.

GEOTHERMAL DRILLING ACTIVITY IN THE AKROPOTAMOS AREA (MACEDONIA, NORTHERN GREECE)

The Akropotamos area constitutes a new geothermal field located in the eastern coastal zone of the Strymonikos Gulf in Macedonia (Northern Greece). After a detailed and systematic reconnaissance study including water temperature measurements at the heads of the existing irrigation and water supply wells, 6 new geothermal wells were constructed. This geothermal drilling program was performed by the Institute of Geology and Mineral Exploration during October 2003 - February 2006. Temperature and fluid conductivity logs were carried out into these boreholes during their drilling and after their completion. Well AKR-1 has a depth of 275 m and produces thermal waters at a temperature of 83o C with artesian flow rate 150 m3 /h and large amounts of dissolved CO2. Well AKR- 2 of 410 m yields 25 m3 /h of waters at 46o C. Well AKR-3 was drilled down to 515 m and the temperature of 88.9o C was measured at 498 m. This well yields about 200 m3 /h CO2-rich geothermal fluids at a temperature of 90o C with artesian flow. Next to this borehole, well AKR-4 was drilled at 180 m penetrating a shallow aquifer with waters reaching 49.7o C. During pumping test with constant flow rate, this well yielded 40 m3 /h water of 48o C. Well AKR-5, 422 deep, was drilled in the western part of the study area close to the Strymon river’s mouth. The temperature of 27.8o C was recorded at 280 m into this borehole. The last well AKR-6 was drilled down to 545 m in the eastern part of the field. The temperature of 38o C was recorded at depth of 503 m. Pumping tests were performed in wells AKR-2 and AKR-4. This geothermal drilling project has resulted in the official characterization of the Akropotamos - Kavala area as a “proven low enthalpy geothermal field”.

Structural compartmentalisation of a geothermal system, the Torre Alfina field (central Italy)

Abstract Recent surging of renewed industrial interest in the exploration of low and medium enthalpy geothermal fields makes the accurate assessment of the geothermal potential essential to minimise uncertainties during both exploration and exploitation. The Torre Alfina field is a case of abandoned, but promising, geothermal field of central Italy where the roles of the internal structural setting and of the recharge areas on the hydrothermal circulation are largely unconstrained. In this paper, field structural data integrated with geomorphic lineament analysis document the occurrence of post-orogenic deformation structures controlling the compartmentalisation of the Torre Alfina geothermal field. Strike-slip and subordinate normal fault systems (with associated network fractures) cut and dislocate the internal architecture of the reservoir and prevent its hydraulic connection with Mount Cetona, considered to be the recharge area and where hydrothermal manifestation, including travertine deposition, occurs. 230Th/234U radiometric dating of superposed travertine units gives 200, 120 and 90 ka respectively, inferred to correspond to the age of the fossil hydrothermal circulation during tectonic activity. The results have been used for illustrating a new geological conceptual model for the Torre Alfina area where the geothermal system is composed of different compartments. Tectonic structures define the main boundaries between compartments, helping the understanding of why productive and non-productive wells were found in apparently similar structural settings within the Torre Alfina field.

Geometric arrangement and operation mode adjustment in low-enthalpy geothermal borehole fields for heating

The efficient operation of ground source heat pump (GSHP) systems with multiple borehole heat exchangers (BHEs) over a lifetime of decades implies an optimized performance of the BHEs and a mitigation of the environmental impact of the system. This paper introduces a new combined optimization approach, which adjusts the BHE positions as well as the individually regulated energy extraction for each single BHE within a given borehole field in conduction dominated media for a given seasonal changing load profile. The optimization of only the BHE positions without optimizing the individual BHE loads nearly produces the same improvement of the underground temperature change of approximately 12% as an optimization of the BHE loads without optimized positioning. The combination of both optimization approaches results in only slightly better results compared to a result achieved by only one of the optimization approaches. Thus for homogeneous fields without groundwater flow, an optimal load assignment can be substituted by an optimal BHE placement, which leads to a considerably reduced complexity of the borehole field.

Power Generation from Low Enthalpy Geothermal Fields by Design and Selection of Efficient Working Fluids for Organic Rankine Cycles

This work addresses the efficient power generation from low enthalpy geothermal fields through the use of a systematic method for the design and selection of heat exchange working fluids tailored for Organic Rankine Cycle (ORC) systems. A systematic methodology is employed that is based on the design of optimum working fluid candidates using a Computer Aided Molecular Design (CAMD) method. The performance of the designed fluids is evaluated using a model of the ORC system that enables simulation and economic design optimization. The performed evaluation also considers additional working fluid characteristics such as safety (toxicity and flammability) and environmental properties (ozone depletion potential and global warming potential) that are equally important to economic efficiency. An overall performance index is developed that facilitates the systematic evaluation of the working fluids for geothermal fields with a broad range of temperature and flowrate characteristics. ORC design and operating constraints are considered representing requirements in cases of power and heat co-generation. The proposed approach is illustrated through a case study involving different types of geothermal fields encountered in Greece. The obtained results reveal useful performance trade-offs among the considered working fluids under various geothermal field conditions.

Revision, calibration, and application of the volume method to evaluate the geothermal potential of some recent volcanic areas of Latium, Italy

The volume method is used to evaluate the productive potential of unexploited and minimally exploited geothermal fields. The distribution of P CO2 in shallow groundwaters delimits the geothermal fields. This approach is substantiated by the good correspondence between zones of high CO 2 flux, and the areal extension of explored geothermal systems of high enthalpy (Monte Amiata and Latera), medium enthalpy (Torre Alfina) and low enthalpy (Viterbo). Based on the data available for geothermal fields either under exploitation or investigated by long-term production tests, a specific productivity of 40 t h −1 km −3 is assumed. The total potential productivity for the recent volcanic areas of Latium is about 28 × 10 3 t h −1, with 75% from low-enthalpy geothermal fields, 17% from medium-enthalpy systems, and 8% from high-enthalpy reservoirs. The total extractable thermal power is estimated to be 2220–2920 MW, 49–53% from low-enthalpy geothermal fields, 28–32% from medium-enthalpy systems, and 19–20% from high-enthalpy reservoirs.

ORIGIN AND QUALITY OF THERMAL GROUNDWATERS IN THE REGION OF FARSALA (E. THESSALY/GREECE)

Farsala Basin presents a remarkable geothermal interest. Areas exhibiting geothermal potential are directly related to faulted zones, represented mainly by cross-faulted systems of E-W, NW-SE and NNE-SSW direction. Thermal waters occur in the areas of Ampelia and Krini in boreholes of 420 m depth. Their temperature ranges between 20,5° and 39,1° C. Thermal waters originate from meteoric waters, which have been infiltrated and heated in great depths, moved towards the surface through faults and hosted in the aquifers of coarse - grained formations find in the area. Their chemical composition is controlled by their contact with the volcanic parts (pillow lavas) of the ophiolithic series. They show alkaline character and low salts concentration. Waters of Ampelia region, which belong to Na-HCO^ type, exhibit temperatures from 27,9° to 39,1° C and low salt concentrations (405- 607 mg/l TDS). On the contrary, waters of Krini area present lower temperatures (20,5° -26,2° C) and higher salt concentrations (734-1850 mg/l TDS). These waters belong to Na-Mg-Ca-HCO^and Na-S04 -Cl-HCO} types. According to chemical geothermometers the study area can be classified to low enthalpy geothermal field, since the estimated thermal liquids temperature in great depths varies from 50° to 70° C.

2D joint inversion of dc and scalar audio-magnetotelluric data in the evaluation of low enthalpy geothermal fields

Audio-magnetotelluric (AMT) and resistivity (dc) surveys are often used in environmental, hydrological and geothermal evaluation. The separate interpretation of those geophysical data sets assuming two-dimensional models frequently produces ambiguous results. The joint inversion of AMT and dc data is advocated by several authors as an efficient method for reducing the ambiguity inherent to each of those methods. This paper presents results obtained from the two-dimensional joint inversion of dipole?dipole and scalar AMT data acquired in a low enthalpy geothermal field situated in a graben. The joint inverted models show a better definition of shallow and deep structures. The results show that the extension of the benefits using joint inversion depends on the number and spacing of the AMT sites. The models obtained from experimental data display a low resistivity zone (<20 ? m) in the central part of the graben that was correlated with the geothermal reservoir. The resistivity distribution models were used to estimate the distribution of the porosity in the geothermal reservoir applying two different approaches and considering the clay minerals effect. The results suggest that the maximum porosity of the reservoir is not uniform and might be in the range of 12% to 24%.

Evaluation of utilisation opportunities of geothermal energy in the Kavala region, Greece, using exergy analysis

Greece has a lot of geothermal energy fields. Due to legal inefficiencies, the exploitation of this renewable energy source remains at very low levels. In this work, the operation of a cogeneration (hot water and electricity) geothermal plant that could be built in Eratino, Greece, is analysed. The research on the development of a low enthalpy geothermal field is investigated as a very essential investment. The building of small geothermal power plants to supply mini-grid power in remote locations with geothermal resources, has proved to be very important. Exergy analysis is used for the evaluation of the efficiency of the exploitable unit. The environmental impacts of the geothermal plant are also examined.

STUDY ON THE EXPLOITATION POSSIBILITY OF THE THERMA-NIGRITA GEOTHERMAL FIELD (PREFECTURE OF SERRES)

The aim of this study is to evaluate the potential of Therma Nigrita low-enthalpy geothermal field and to examine the possibility of exploitation. Six geothermal fluid samples and two cold-water samples were obtained from eight boreholes situated in the Therma field of Nigrita. Field measurements, as well as laboratory determinations using classic and modern methods of analyses were carried out. The temperature of the geothermal fluids ranges from 38,5 up to 62,5°C; the discharge rates of the boreholes range from 40 up to 70 m3/h. These data lead to the conclusion that the field is exploitable. Due to high As and Li contents and in order to avoid environmental impacts, it is essential to reinject the waste geothermal fluids into the geothermal reservoir. For the exploitation of the geothermal field, the applications of district heating and cooling of a part of Nigrita Municipality using heat pumps, in combination with greenhouse applications, are proposed. In order to save energy and reduce the capital cost, the above applications have to be placed in cascade. The energy production cost, including also the capital amortisation cost, of the above application amounts to 0.0226 €/kWh. The proposed geothermal applications have a significant economic advantage over the use of fossil fuels. Additionally, there is an important environmental benefit from avoiding the emission of severe quantities of CO2 (&gt;8,000 tons annually), which would be emitted in case of oil use.

Hydrogeological and isotopic survey of geothermal fields in the Buyuk Menderes graben, Turkey

The main high and low enthalpy geothermal fields in the Buyuk Menderes graben (Western Anatolia) and their reservoir temperatures are as follows: Kizildere (242 °C), Germencik (232 °C), Aydin-Ilicabasi (101 °C), Yılmazkoy (142 °C), Salavatli (171 °C), Soke (26 °C), Denizli -Pamukkale (36 °C), Karahayit (59 °C), Golemezli (101 °C) and Yenice (70 °C). The geothermal systems are controlled by active graben faults. The reservoir rocks in the geothermal fields are the limestone and conglomerate units within Neogene sediments and the marble-quartzite units within Paleozoic metamorphic formations. There are clear δ 18O shifts from the Mediterranean Meteoric Water Line (MMWL) in the Kizildere, Germencik and Aydin fields, where a good relation between high temperatures and δ 18O shift has also been observed, indicating deep circulation and water rock interactions. In the Pamukkale, Karahayit, Golemezli and Yenice fields and in Soke region, low temperatures, small isotope shifts, shallow circulations and mixing with shallow cold water have been noted.

Computational methods for planning and evaluating geothermal energy projects

In planning, designing and evaluating a geothermal energy project, a number of technical, economic, social and environmental parameters should be considered. The use of computational methods provides a rigorous analysis improving the decision-making process. This article demonstrates the application of decision-making methods developed in operational research for the optimum exploitation of geothermal resources. Two characteristic problems are considered: (1) the economic evaluation of a geothermal energy project under uncertain conditions using a stochastic analysis approach and (2) the evaluation of alternative exploitation schemes for optimum development of a low enthalpy geothermal field using a multicriteria decision-making procedure.

Application of the SP technique over Lagadas low enthalpy geothermal field, Greece

In order to verify the applicability of the SP gradient method as a tool for geothermal exploration, Lagadas low enthalpy geothermal field was used as a test site. A total of 63 line km was surveyed using the SP gradient method along 10 profiles covering the main geothermal field area. The compiled SP map correlates in a satisfactory way with other geological and geophysical information available. Detected SP anomalies were inverted to causative polarized planes and their relationship with existing deep fractures in the basement is investigated. As a result, two main fracture zones were detected, which were electrically polarized, and coincide with already known similar tectonic features identified by other geological and geophysical methods. Circulation of hot water in deep permeable fracture zones is considered to be the originating mechanism of the observed SP anomalies.