High Enthalpy Geothermal Resources Research Articles

GIS-based AHP model for selecting the best direct use scenarios for medium to low enthalpy geothermal resources with hot springs in central and Western Kenya

Medium to low enthalpy geothermal resources (MLEGRs) in various Eastern African countries, Djibouti, Ethiopia, Kenya, Uganda, Tanzania, Rwanda, and Malawi, have received little attention from policymakers in the energy sector. Policymakers from these countries prioritize developing high-enthalpy resources for electric power production. Hence, many MLEGRs remain unused since they are assumed to pose higher risks of drilling unproductive deep wells. Besides, funding institutions prioritize high-enthalpy geothermal resources. Some MLEGRs have warm-to-hot springs with considerable flow rates and chemical constituents with varying concentrations. This study introduces a novel approach, using hydrogeochemical analysis of hot spring waters and a GIS-based AHP model, to select the best direct use scenarios for the warm/hot springs emanating from MLEGRs in central and western Kenya. The model is validated by contemporary commercial usage of the hot springs and similar studies in the study area. The stable isotope analysis revealed that the hydrothermal systems in Kenya are majorly recharged by meteoric water. In contrast, Kenya Rift Valley endorheic lakes, such as Lake Naivasha, Lake Nakuru, Lake Magadi, Lake Baringo, Lake Bogoria, and Lake Turkana, partly recharge some. Hence, they pose low risks of drying up during development and exploitation for thermal energy. The over 150 hot springs in Kenya produce warm to hot water with a thermal capacity of over 275 MWt. Hence, by harnessing the hot spring resources, Kenya can raise its direct use capacity from the current 18.5 MWt to about 100–200 MWt without drilling shallow or deep wells. The hot springs best suited for domestic use and aquacultural pond heating were selected as Narosura, Majimoto, Olchorro, Kipsegon, Kijabe, and Eburru. Those best suited for spas, bathing/ swimming pools, and volcanic geotourism were Lake Bogoria, Arus, Homa Hills, and Kariandusi. Overall, Lake Bogoria, Homa Hills, and Narosura hot springs were rated the best for direct use of hot springs.

Use of cold waters geochemistry as a geothermal prospecting tool for hidden hydrothermal systems in Réunion Island

Most untapped high-enthalpy geothermal resources are blind, meaning lacking surface evidence of their existence. The first step in their discovery is to find evidence of hydrothermal activity. Here we apply an approach based on the geochemistry of cold waters, which allowed us to identify evidence of the existence of a hydrothermal system at Piton de la Fournaise volcano (Réunion Island), and constrain its location. This approach uses the concentrations in B, Li, SO4, F, Mo, P, V, As and HCO3 and the isotopic ratios δ13C and δ11B as geochemical markers of hydrothermal activity that can be used even in waters with extremely low ion content (Electrical conductivity <80 µS/cm), and even when their geochemical composition is mainly controlled by other processes. This noninvasive approach is easy to implement and can be applied wherever the presence of a blind geothermal system is suspected.

Geothermal energy exploitation in an island-based 100% renewables strategy. Case study of Tenerife (Spain)

The large-scale integration of non-dispatchable renewable energy must be carefully planned, especially in poorly robust electrical energy systems. Tenerife is the most populated of the islands in the Canary Archipelago (Spain) and has an isolated electrical system. It is envisaged for the horizon of 2040 that the island will have a high contribution of non-dispatchable renewable energies (fundamentally wind and solar photovoltaic). Tenerife also has exploitable high enthalpy geothermal resources. An energy planning model is implemented in this paper based on which different scenarios with high non-dispatchable renewable energy penetration in the island's electrical system are simulated. Geothermal energy is also incorporated in the simulations as a dispatchable renewable energy source, with the power required sized according to the hypotheses of each scenario. The results are compared according to different technical and economic parameters. An evaluation is also made of the influence that the capacity of the electrical system to take on higher non-dispatchable renewable power and the presence of energy accumulation systems might have on the minimization of losses in the non-dispatchable renewable energy capacity factor. The results of the simulated scenarios show that geothermal energy could meet up to 28.8% of the island's electrical energy demand, increasing the stability, flexibility and supply guarantee of system. A 100% renewable system could be possible through the incorporation of this energy source and the planning of energy accumulation systems. In the case study, the economic saving for Spain's electrical system could exceed 400 €million per year.

Energy capacity of the geothermal resource and its integration in the electrical energy demand of the island of Tenerife (Spain)

One of the main strategies to maximize renewable energy penetration in electrical systems is to optimize their dispatchable capacity. One of the benefits of geothermal energy, as a renewable energy source, is its high dispatchability. The isolated electrical energy system of Tenerife (one of the 8 islands of the Canary Archipelago) is highly dependent on fossil fuels. The advanced state of maturity of the geothermal exploration of Tenerife positions the island with a high degree of probability as one of the few regions in Spain with high-enthalpy geothermal resources. This paper reports on a study undertaken of the island’s geothermal potential which involved calculation of the heat stored in geothermal reservoirs and the identification of zones of interest for exploitation of this resource and its energy capacity. Among the results obtained, 3 areas of interest were identified for the exploitation of geothermal energy with a total installable electrical power of 117.8 MW, which would increase the renewable contribution to the island’s daily demand by over 20% as well as contribute to maximizing the flexibility and stability of the electrical energy supply in a scenario of high renewable energy penetration.

Reliable renewable power production by modeling of geothermal assisted solar chimney power plant

The growing concern about the impact of climate change has highlighted the importance of renewable resources. Wind, geothermal, and solar energy are some of the most natural renewable energy sources, dominated by their availability and efficiency. Currently, medium-low enthalpy geothermal is exploited less than high-enthalpy geothermal resources. In addition, the variable nature of solar radiation is a significant problem for the solar systems resulting from the solar chimney power plant's discontinued operation. These geothermal resources can feed into the solar chimney power plant to generate electricity and resolve the solar system discontinuously. In the present research, a geothermal hot spring with a temperature of 75 °C in Khorasan, Iran, has been investigated as a case study. By developing a finite volume Computational Fluid Dynamics model, the system performance has been evaluated. Hybridizing these two energy sources declares a significant improvement in the power plant's performance. Increasing the thermal flux of hybrid systems by 200 kW/m2 designates a 17% increase in power generation of the geothermal-solar system at a specific hour of the day, in comparison with a stand-alone solar chimney. Moreover, a geothermal–solar chimney power plant in the coldest month of the year showed the same output power as solar chimney power plants could generate in the warmest month of the year. Annual averaged thermal flux productivity under the hybrid system is 585.12% larger than sole geothermal spring production. The hybrid system model produces 319.5 MWh while the stand-alone system generates 263.9 MWh of energy throughout the year. Economic analysis shows that the proposed system is one-tenth affordable considering energy prices in Iran.

Exploration of deep-seated geothermal reservoirs in the Canary Islands by means of soil CO2 degassing surveys

The Canary Islands are the only Spanish territory that holds potential for high enthalpy geothermal resources, although there is no evidence in the islands of hydrothermal fluid discharges in the surficial environment except for Teide volcano fumaroles in Tenerife. We herein report the results of several diffuse carbon dioxide (CO2) degassing surveys carried out at six mining licenses across Tenerife (Berolo, Guayafanta, Abeque, Garehagua and Garehagua II) and Gran Canaria (Atidama), covering a total of 640 km2 and more than 3230 sampling sites. Selected geochemical molar ratios, spatial distribution of CO2 efflux, statistical-graphical analysis of CO2 efflux, isotopic composition of CO2 (δ13C–CO2), the calculated volcano-hydrothermal contribution of CO2 and the deep-seated CO2 efflux were studied. These data were combined and used for geothermal exploration, demonstrating an effective reconnaissance strategy that reduces risk and cost. Garehagua II, Garehagua (both located in the north-south volcanic rift of Tenerife) and Abeque (located in the northwest volcanic rift of Tenerife) are, in this order, the mining licenses studied that showed the highest potential to contain geothermal resources, based on the geochemical indicators ranking proposed.

Geological field investigation for the assessment of the low-grade geothermal resources from volcanic terrains of the Island of Salina (Aeolian Islands, Italy)

The subsoil as a “thermal reservoir” is a modern concept that is leading to continuous developments of innovative methods of energy production. If volcanic areas have been so far considered suitable for exploitation of medium-to-high enthalpy resources, it is also true that an incredible potential confined to low grade resources is available. The geological background of Sicily makes the island as one of the most suitable contexts of southern Italy where geothermal resources could have great potential to increase their whole usage. Several active volcanic zones or areas at high hydrothermalism offer advantageous exploitation from low to high enthalpy geothermal resources. Here we present a case study from Santa Marina Salina (Aeolian Island Arc) with a detailed field survey providing information on lithostratigraphic features and on hydrogeological conditions of the area. The study is aimed at testing the thermal conductivity distribution at various depths by means of a theoretical model. Such an approach allowed the definition of the most suitable areas and their low-grade geothermal potential through different thematic maps for thermal conductivity in the shallow subsurface (0-150 m). Collected data become crucial for correct sizing of low-enthalpy geothermal installations, leading to optimization of the final planned technical solutions efficiency.

Deep-seated Geothermal Resources of the Parana Basin

Updated data sets on terrestrial heat flow and thermal springs have been employed in outlining the nature of deep-seated geothermal resources of the Parana basin. A 1o x1o grid system was adopted for data processing and in determinations of vertical distributions of excess temperatures. The results obtained have led to an improved understanding of the occurrence of high temperature geothermal resources and allowed estimates of associated resource base. It has been possible to identify more than 20 crustal blocks where the resource base per unit area, referred to the accessible depth limit of 6 km, are in the range of 2x1011 to 9x1011 Joules. There are indications pointing to occurrence of medium temperature geothermal resources at depths of 4 to 6 km in several sectors of the central and western parts of the basin. The area extent of such blocks has dimensions of several tens of kilometers. Most high temperature resources occur within the well-known sectors of fault-controlled magmatic activity associated with the eruption of Serra Geral flood basalts. In addition, isolated pockets of high enthalpy geothermal resources are found to be present along the northwestern border. The results have also allowed better assessments of low temperature resources of the Guarani aquifer system, which span over large areas of southern Brazil, western Uruguay and northern Argentina.

Power plant selection for medium to high enthalpy geothermal resources of Turkey

A geothermal power plant model depends on the variations not only the temperature, but also, geochemical, and physical features of resources. Most of the geothermal brines in the world and in our country contain dissolved minerals and NCGs (non-condensable gases). These minerals precipitate from the solution and non-condensable gases flash depending on the changes of temperature and pressure during production and re-injection processes.In this study, common geochemical characteristics of geothermal resources of Turkey are briefly mentioned; chemical conditions for operation and re-injection processes are discussed. Taking into account of the above features, “combined power plants” devised by a combination of single-double flash processes with atmospheric condenser and “binary” cycles are introduced. They are compared thermodynamically and economically with each other and the ones from previous studies.Power capacity and efficiency of Combined Cycle Model-2 have been found 38.13 MWe and 14.1%, respectively. Combined Cycle Model-3 with single flash atmospheric process and binary presents these figures as 37.20 MWe and 13.4%, respectively. Economically, although the previous model has a slight edge in ROR (rate of return) (27.5% over 27%) the second one should be preferred because of potential silica scaling potential problem in the first one.

Assessment of high enthalpy geothermal resources and promising areas of Chile

This work aims to assess geothermal power potential in identified high enthalpy geothermal areas in the Chilean Andes, based on reservoir temperature and volume. In addition, we present a set of highly favorable geothermal areas, but without enough data in order to quantify the resource. Information regarding geothermal systems was gathered and ranked to assess Indicated or Inferred resources, depending on the degree of confidence that a resource may exist as indicated by the geoscientific information available to review. Resources were estimated through the USGS Heat in Place method. A Monte Carlo approach is used to quantify variability in boundary conditions. Estimates of total Indicated resource are confined to 3 geothermal systems; Apacheta, El Tatio and Tolhuaca, yielding a total value of 228 ± 154MWe. The estimates of the total Inferred resources for Chile include 6 geothermal systems and yield a total value of 431 ± 321MWe. Standard deviation reflects the high variability of reservoir specific parameters for each system. A set of 65 favorable geothermal areas are proposed as the most likely future development targets. Eight of them have initial exploration results that suggest they are highly favorable targets as potential geothermal resources.

Diffuse Helium and Hydrogen Degassing to Reveal Hidden Geothermal Resources in Oceanic Volcanic Islands: The Canarian Archipelago Case Study

We report herein the results of soil gas geochemistry studies, focused mainly on nonreactive and/or highly mobile gases such as He and H2, in five mining licenses at Tenerife and Gran Canaria, Canary Islands, Spain, during 2011–2014. The primary objective was to sort the possible geothermal potential of these five mining licenses, thus reducing the uncertainty inherent to the selection of the areas with highest geothermal potential for future exploration works. By combining the overall information obtained by the statistical–graphical analysis of the soil He and H2 data, the spatial distribution of soil gas concentrations and the analysis of selected chemical ratios of the soil gas to evaluate the influence of deep-seating degassing, two of the five mining licenses (Garehagua and Abeque, both located in Tenerife Island) seemed to show the highest geothermal potential. These results will be useful for future implementation and development of geothermal energy in the Canaries, the only Spanish territory with potential high-enthalpy geothermal resources, thus the most promising area for high-enthalpy geothermal installations.

On the environmental suitability of high- and low-enthalpy geothermal systems

This article addresses the life cycle assessment of (i) power generation in a binary-cycle power plant using high-enthalpy geothermal resources, and (ii) heat generation in a closed-loop geothermal heat pump system using low-enthalpy resources. For the geothermal power system, production and injection wells show a high contribution to the environmental impacts, mainly due to activities such as drilling and casing. Power plant operation is also identified as an important source of impact because of working fluid losses. A favourable life-cycle energy balance is estimated for this system. Furthermore, when compared to fossil electricity, geothermal electricity is generally found to be a promising alternative. For the geothermal heat system, the electricity demands for heat generation and use are the main sources of impact. An unfavourable life-cycle energy performance is predicted for this system. When compared to fossil heat, the environmental suitability of geothermal heat highly depends on the availability of eco-friendly electrical grids.

New geochemical investigations in Platanares and Azacualpa geothermal sites (Honduras)

Platanares and Azacualpa geothermal sites of Honduras are located in an inner part of the Caribbean Plate far from the active volcanic front of Central America. Here geology indicates that there are not the conditions for the occurrence of shallow magmatic heat sources for high-enthalpy geothermal resources. Geothermal perspectives are related to the possibility of a deep circulation of meteoric water along faults and the storage of the heated fluid in fractured permeable reservoirs. Geochemical geothermometers indicate a temperature for the deeper part of the geothermal reservoir close to 200°C for Platanares and of 150–170°C for Azacualpa. Calcite scaling, with subordinate silica deposition has to be expected in both sites. CO2 soil flux investigations have been carried out in both areas and reveal the presence of positive anomalies likely corresponding to the presence at depth of fractured degassing geothermal reservoirs. Compared with the geothermal areas of Central Italy whose reservoirs are hosted in carbonate rocks, e.g. Latera (Chiodini et al., 2007), the CO2 soil flux measured in Honduras is significantly lower (mean of 17g/m2day at Platanares and of 163g/m2day at Azacualpa) probably because of the dominant silicate nature of the deep reservoirs.

Possibilities for electricity production from geothermal energy in Slovenia in the next decade

This article is intended to raise awareness of the public, with the aim that anyone can judge reality and accuracy of records that appear in the media on the exploitation of geothermal energy. It provides a comprehensive overview of geothermal systems, potential of hydrothermal and enhanced geothermal systems, of mechanisms and characteristics of middle and high enthalpy geothermal resources. It also deals with a mode of their conversion into electricity. Featured are the main factors affecting the decision on effectiveness of conversion of geothermal energy into electricity. Given are the review of the research necessary to establish the geothermal potential and assessment of technological and economic possibilities of installing geothermal power plants in Slovenia. The paper also describes the state of knowledge of middle- and high temperature geothermal resources in Slovenia with initial conditions for constructing geothermal power plants. In addition, we present theoretical calculations of the conversion efficiency of geothermal energy into electricity with conventional turbines and present some problems for the exploitation of geothermal energy, which are associated with additional costs and further reduce the efficiency of investment. Described are the characteristics and performance of binary geothermal power plants and foreign experience in obtaining electricity from the EGS (Enhanced Geothermal System). We also address the overlapping of the oil and gas industry with the operation of the EGS and the possibility of exploiting oil and gas wells for producing the geothermal electricity.

Reconnaissance assessment of the prospects for development of high-enthalpy geothermal energy resources, Montserrat

Abstract The Soufriere Hills Volcano on Montserrat has been in eruption since 1995. Before then, a number of hot springs and fumaroles high on the volcanic edifice attested to the presence of hydrothermal circulation systems. All of these features were buried beneath thick deposits of volcanic ash during the early years of the eruption. However, examination of low-lying sites in the vicinity of the abandoned town of Plymouth has revealed the persistence of a zone of hot (≤64 °C) groundwater discharge in a narrow valley that opens onto the northern beaches of the town. This small valley has not been significantly affected by ash deposition, with any airfall deposits having been subsequently washed downstream during periods of rain. The seepages and small springs in this zone all emit Na–Cl groundwaters, which appear from the concentrations of major ions and B and Li to be hydrothermally altered seawaters that have undergone extensive rock–water interaction at depth. Taken together with previously published volcanological observations, the persistence of this hydrothermal system throughout the sustained eruption period suggests that a robust hydrothermal circulation system exists at depths of several hundred metres in an area that closely adjoins the still-inhabited half of the island. Comparison with similar volcanogenic hydrothermal systems in the Caribbean and elsewhere suggests that there is significant potential for development of high-enthalpy geothermal energy resources in this vicinity. Using a portable well-head generating unit, a single successful borehole in this area could reasonably be expected to yield up to 5 MW of electrical power. This output significantly exceeds the current peak electricity demand on the island ( c . 3.5 MW). In concept, it would be possible to exploit any excess capacity to operate an electrolysis plant to produce hydrogen for use in vehicles on the island. Establishing energy self-sufficiency would be a major step towards the economic and social regeneration of this devastated island, with the further possibility of increasing prosperity in the future through export of surplus energy to nearby non-volcanic islands.

Geothermal exploration of Roccamonfina volcano, Italy

The Quaternary volcano of Roccamonfina, located within the Roman high-potassic province, developed in the time interval 1.5-0.25 Ma, initially as a stratocone which later was partially destroyed by phreatomagmatic explosions. The last evolutionary stage is represented by intra-crater latite domes and trachybasalt flows ( ca. 15 Ma). Geophysical data, primarily from gravity and MT/EM surveys, demonstrate that the volcano formed at a complex structural intersection above a NE-trending Pliocene graben. The same data, confirmed by the result of an 887 m test well, indicate that the volcano has not undergone caldera subsidence of the type exemplified by the Valles Caldera of New Mexico, but more probably had a series of post-stratocone lateral blasts akin to the 1980 Mount St. Helens eruptions. Hot springs near the western foot of the volcano, and the presence of young highly-evolved rocks suggested that the area could have geothermal potential. However, geochemical and isotopic data provide no indication of the present existence of a hydrothermal system, whilst the lack of alteration (both at the surface and in the test well) suggest that no such system existed in the past. Geophysical data show no anomalous features which might be associated with a geothermal reservoir or with hydrothermal alteration. These negative conclusions, strongly supported by the low temperature of the test well (35°C at 886 m), demonstrate fairly conclusively that Roccamonfina is non-prospective for high-enthalpy geothermal resources.

Post-orogenetic magmatic activity and related geothermal resources in southern Tuscany, Italy

A wide area of central Italy, located along the Tyrrhenian coast, is characterized by recent magmatic activity, regional uplifting and abundant thermal manifestations. The area, which includes southern Tuscany and parts of northern Latium, is bounded to the north by the Arno River valley, to the east by the Chiana valley and Lake Trasimeno, to the south by the Tiber valley and to the west by the important normal fault system controlling the Tyrrhenian coast. The area is also well-known for the frequent occurrences of young mineral deposits and the presence of abundant high enthalpy geothermal resources: the dry-steam fields of Larderello and Mt. Amiata, among the largest in the world, with a present electric installed capacity of 459 MW (1984). The understanding of the origin of these phenomena and of the processes which led to the formation of the natural resources characterizing the area (geothermal, mineral etc.), might represent a valuable exploration tool and lead to a further expansion of present exploitation.

The status of high enthalpy geothermal exploration in the developing countries

High enthalpy geothermal resources suitable for electric power production occur in more than 50 developing countries, although by the end of 1983 only nine had installed production capacity in 14 fields totalling just over 1200 MW. One of the major obstacles to accelerated geothermal development in the developing countries is the high-risk exploratory drilling phase, where the number of countries seeking finance outnumbers those actually drilling by a factor of 3 to 1. The United Nations Revolving Fund for Natural Resources Exploration is seeking to alleviate this situation. An overview of geothermal activities in the developing countries is presented.

European Geothermal Drilling Experience. Problem Areas and Case Studies

Geothermal drilling has long been restricted in Western Europe to the sole dry steam field of Larderello in Italy. In the last few years, a wider experience is building up as a consequence of intensified exploration and development programs carried out for evaluation and production of both low- and high-enthalpy geothermal resources. A sample of some 40 boreholes indicates the problem areas which are given.