Low enthalpy geothermal energy utilisation schemes for greenhouse and district heating at Traianoupolis Evros, Greece

A socio-economic study has been made of the possible use of low enthalpy geothermal resources for district and greenhouse heating in the Traianoupolis Evros region. The thermal energy potential of the Aristino-Traianoupolis geothermal field has been estimated at 10.8 MW_th (discharge temperature of 25 °C). Geothermal wellhead water temperatures range from 53 to 92 °C, from 300 m deep wells yielding over 250 m³/h. Our conclusions show, amongst the different scenarios examined and on the basis of a market study, that utilisation of this geothermal energy capacity for district heating of nearby villages, and/or greenhouse heating directed at serving local vegetable markets, would be an attractive investment.     

Geothermal development in Hungary—country update report 2000–2002

This paper describes the status of geothermal energy utilization—direct use—in Hungary, with emphasis on developments between 2000 and 2002. The level of utilization of geothermal energy in the world increased in this period and geothermal energy was the leading producer, with 70% of the total electricity production, of all the renewable energy sources (wind, solar, geothermal and tidal), followed by wind energy at 28%. The current cost of direct heat use from biomass is 1–5 US¢/kWh, geothermal 0.5–5 US¢/kWh and solar heating 3–20 US¢/kWh. The data relative to direct use in Hungary decreased in this period and the contribution of geothermal energy to the energy balance of Hungary, despite significant proven reserves (with reinjection) of 380 million m³/year, with a heat content of 63.5 PJ/a at ΔT=40 °C, remained very low (0.25%). Despite the fact that geothermal fluids with temperatures at the surface higher than 100 °C are available, no electricity has been generated. As of 31 December 2002, the geothermal capacity utilised in direct applications in Hungary is estimated to be 324.5 MW_t and to produce 2804 TJ/year. Geothermal heat pumps represent about 4.0 MW_t of this installed capacity. The quantity of thermal water produced for direct uses in 2002 was approximately 22 million m³, with an average utilization temperature of 31 °C. The main consumer of geothermal energy is agriculture (68% of the total geothermal heat dedicated to direct uses). The geothermal water is used only in five spas for space heating and sanitary hot water (SHW), although there are 260 spas in the country, and the thermal water produced has an average surface temperature of 68 °C. The total heat capacity installed in the spas is approximately 1250 MW_t; this is not provided by geothermal but could be, i.e., geothermal could provide more than three times the geothermal capacity utilized in direct uses by 31 December 2002 (324.5 MW_t).     

Structure and hydrology of the Ogiri field, West Kirishima geothermal area, Kyushu, Japan

The geothermal system in the West Kirishima area is controlled by a system of faults and fractures oriented along two main directions, northwest to southeast and east–northeast to west–southwest. The Ginyu fault extends through the Ogiri field in the Ginyu area, which is one of the east–northeast to west–southwest striking faults in this area. This fault is the reservoir target for developing the geothermal resources in the Ogiri field. The Ginyu fault is a near planar fracture with a uniform temperature of 232°C and has near-neutral pH, chloride fluids. Based on the results of a detailed analysis of the Ginyu fault, all production wells drilled in the Ogiri field intersected the Ginyu fault reservoir successfully, securing steam production for a 30 MW_e power plant. A typical fracture-type geothermal model for the Ogiri field was developed on the basis of the geology, electric and geophysical logs, fluid chemistry, and well test data.     

Classification of geothermal resources in Poland by exergy analysis—Comparative study

Geothermal resources in Poland are of growing importance for the production of renewable energy. The total installed geothermal capacity (including heat pumps) at the end of 2008 was ca. 281 MW_t, while heat sales about 1501 TJ. Poland is characterised by low-temperature geothermal resources connected mostly with the Mesozoic sedimentary formations. In the paper the estimation of thermodynamic potential of Polish geothermal fields in comparison with selected global resources was presented. Geothermal resources were classified with reference to their specific exergy and specific exergy index (SEI). These indices define the quality of the energy content of a geothermal fluid better than conventional temperature criterions.     

Geothermal space heating

The use of geothermal resources for space heating dominates the direct use industry, with approximately 37% of all direct use development. Of this, 75% is provided by district heating systems. In fact, the earliest known commercial use of geothermal energy was in Chaudes-Aigues Cantal, France, where a district heating system was built in the 14th century. Today, geothermal district space heating projects can be found in 12 countries and provide some 44,772 TJ of energy yearly. Although temperatures in excess of 50 °C are generally required, resources as low as 40 °C can be used in certain circumstances, and, if geothermal heat pumps are included, space heating can be a viable alternative to other forms of heating at temperatures well below 10 °C.     

Geothermal resources of Hachijojima

Hachijojima is a gourd-shaped volcanic island in the Pacific Ocean. Nishiyama and Higashiyama volcanoes consist of basalt lava and associated pyroclastic rocks. A promising geothermal resource was found in south Higashiyama, associated with an uplift of Tertiary rocks consisting of mainly andesite lava and related pyroclastic rocks, overlain by Quaternary volcanic rocks. Steep high-temperature (over 250°C) and high-pressure gradients occur in the deeper portion of the system near the Tertiary–Quaternary contact, indicating the presence of a cap rock. The cap rock formed by deposition of hydrothermal minerals. Geothermal fluid ascends from the deeper portions to shallow depths along vertical fractures through the cap rock. These vertical fractures form the geothermal reservoir in the Tertiary formation. Three wells were drilled into these vertical fractures, and approximately 30 t/h of superheated steam was obtained from each well during flow tests. The geothermal fluid is mainly a mixture of seawater and meteoric water in an approximate ratio of 1 to 2, based on chemical analyses, with a portion of volcanic gas included. At present a 3.3 MW_e, geothermal power plant is being constructed here.     

Aluto-langano geothermal field, ethiopian rift valley: physical characteristics and the effects of gas on well performance

This study, which focuses on the Aluto-Langano geothermal field, is part of the ongoing investigations of the geothermal systems in the Ethiopian Rift Valley. Aluto-Langano is a water-dominated gas-rich geothermal field, with a maximum temperature close to 360°C, in the Lakes District region of the Ethiopian Rift Valley. The upflow zone for the system lies along a deep, young NNE trending fault and is characterized by boiling. As a result, the deep upflow zone loses some water as steam and produces a cooler saline shallow aquifer. The high partial pressure of carbon dioxide (about 30 bar in the reservoir) depresses the water table and restricts boiling to deeper levels. The main aquifer for the system is in the Tertiary ignimbrite, which lies below 1400 m. The capacity of the existing wells is close to 7 MW_c; the energy potential of the area is estimated to be between 3000 and 6000 MW_t yr km⁻³, or 10–20 MW_c km⁻³ for over 30 years.     

World geothermal power generation in the period 2001–2005

A review has been made of all the country update papers submitted to the World Geothermal Congress 2005 (WGC2005) from countries in which geothermal electricity is currently being generated. The most significant data to emerge from these papers, and from follow-up contacts with representatives of these countries, are: (1) a total of 24 countries now generate electricity from geothermal resources; (2) the total installed capacity worldwide is approximately 8930 MW_e, corresponding to about 8030 MW_e running capacity and electric energy production is nearly 57,000 GWh (early 2005 data); (3) Costa Rica, France (Guadeloupe), Iceland, Indonesia, Italy¹, Kenya, Mexico, Nicaragua, Russia, and the USA have increased the capacity of their power plant installations by more than 10% with respect to the year 2000; (4) the new members of the geothermal electricity generating community comprise Austria, Germany and Papua New Guinea; (5) the installed capacity in Argentina and Greece is now null since their geothermal power plants have been dismantled; (6) nineteen countries have carried out significant geothermal drilling operations since 2000, with 307 new wells drilled.     

Sustainability analysis of the Ahuachapán geothermal field: management and modeling

The Ahuachapán geothermal field (AGF) is located in north western El Salvador. To date, 53 wells (20 producers and 8 injectors) have been drilled in the Ahuachapán geothermal field and the adjacent Chipilapa area. Over the past 33 years, 550 Mtonnes have been extracted from the reservoir, and the reservoir pressure has declined by more than 15 bars. By 1985, the large pressure drawdown due to over-exploitation of the resource reduced the power generation capacity to only 45 MW_e. Several activities were carried out in the period 1997–2005 as part of “stabilization” and “optimization” projects to increase the electric energy generation to 85 MW_e, with a total mass extraction of 850 kg/s.     

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 δ¹⁸O shifts from the Mediterranean Meteoric Water Line (MMWL) in the Kizildere, Germencik and Aydin fields, where a good relation between high temperatures and δ¹⁸O 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.     

Geothermal resources in Algeria

The geothermal resources in Algeria are of low-enthalpy type. Most of these geothermal resources are located in the northeastern of the country. There are more than 240 thermal springs in Algeria. Three geothermal zones have been delineated according to some geological and thermal considerations: (1) The Tlemcenian dolomites in the northwestern part of Algeria, (2) carbonate formations in the northeastern part of Algeria and (3) the sandstone Albian reservoir in the Sahara (south of Algeria). The northeastern part of Algeria is geothermally very interesting. Two conceptual geothermal models are presented, concerning the northern and southern part of Algeria. Application of gas geothermometry to northeastern Algerian gases suggests that the reservoir temperature is around 198 °C. The quartz geothermometer when applied to thermal springs gave reservoir temperature estimates of about 120 °C. The thermal waters are currently used in balneology and in a few experimental direct uses (greenhouses and space heating). The total heat discharge from the main springs and existing wells is approximately 642 MW. The total installed capacity from producing wells and thermal springs is around 900 MW.     

Preliminary evaluation of soufriere geothermal field, St. Lucia (Lesser antilles)

Geological, geochemical and geophysical studies have been carried out in the Soufrière caldera, St. Lucia, Lesser Antilles. The results are in accordance with the data obtained from previously drilled wells. In particular, these studies have also been used to: (i) determine the extent of the heat anomaly; (ii) indicate the levels containing hot geothermal fluids for high enthalpy exploitation; (iii) estimate the nature and extent of the reservoir; (iv) construct a preliminary model of the geothermal system, with a fluid at 220°C and a deeper one at about 350°C, both originating from a concentrated brine. Heat flux is estimated to be 6–7 times the average terrestrial value (250 – 290 mW/m²); (v) determine the most favourable areas for deep drilling.     

The Iceland Deep Drilling Project: a search for deep unconventional geothermal resources

The Iceland Deep Drilling Project (IDDP) is a long-term program to improve the economics of geothermal energy by producing supercritical hydrous fluids from drillable depths. Producing supercritical fluids will require the drilling of wells and the sampling of fluids and rocks to depths of 3.5–5 km, and at temperatures of 450–600 °C. The IDDP plans to drill and test a series of such deep boreholes in the Krafla, Nesjavellir and Reykjanes geothermal fields in Iceland. Beneath these three developed high-temperature systems frequent seismic activity continues below 5 km, indicating that, even at supercritical temperatures, the rocks are brittle and therefore likely to be permeable, even where the temperature is assumed to exceed 550–650 °C. Temperature gradients are greater and fluid salinities smaller at Nesjavellir and Krafla than at Reykjanes. However, an active drilling program is underway at Reykjanes to expand the existing generating capacity and the field operator has offered to make available one of a number of 2.5 km deep wells to be the first to be deepened to 5 km by the IDDP. In addition to its potential economic significance, drilling deep at this location, on the landward extension of the Mid-Atlantic Ridge, is of great interest to the international science community. This paper examines the prospect of producing geothermal fluids from deep wells drilled into a reservoir at supercritical temperatures and pressures. Since fluids drawn from a depth of 4000–5000 m may prove to be chemically hostile, the wellbore and casing must be protected while the fluid properties are being evaluated. This will be achieved by extracting the fluids through a narrow retrievable liner called the “pipe”. Modelling indicates that if the wellhead enthalpy is to exceed that of conventionally produced geothermal steam, the reservoir temperature must be higher than 450 °C. A deep well producing 0.67 m³/s steam (2400 m³/h) from a reservoir with a temperature significantly above 450 °C could, under favourable conditions, yield enough high-enthalpy steam to generate 40–50 MW of electric power. This exceeds by an order of magnitude the power typically obtained from a conventional geothermal well in Iceland. The aim of the IDDP is to determine whether utilization of heat from such an unconventional geothermal resource at supercritical conditions will lead to increased productivity of wells at a competitive cost. If the IDDP is an economic success, this same approach could be applied in other high-temperature volcanic geothermal systems elsewhere, an important step in enhancing the geothermal industry worldwide.     

High-temperature measurements in well WD-1A and the thermal structure of the kakkonda geothermal system, Japan

The New Energy and Industrial Technology Development Organization (NEDO) drilled well WD-1a between 1994 and 1995 in the Kakkonda geothermal field as part of their Deep Seated Geothermal Resources Survey project. High-temperature measurements were carried out in WD-1a. Logging temperatures above 414°C were confirmed at 3600 m and 3690 m depth after 82 h standing time. Simple Horner extrapolations based on observed temperatures up to 82 h after shut-in suggested a temperature of about 500°C at 3500 m depth. Temperatures between 500°C and 510°C were also confirmed at 3720 m depth after 129–159 h standing time, using calibrated melting .tablets. These are the highest temperatures measured in a geothermal well. These results suggest a thermal structure consisting of three layers. Layer one is a shallow permeable zone of the reservoir, at less than 1500 m depth, at 230°C to 260°C. The second layer is a deep zone of the reservoir, which is less permeable and has a temperature of 350°C to 360°C from 1500 m to about 3100 m depth. The third layer is a zone of heat conduction. The transition between the hydrothermal-convection zone and the deeper heat-conduction zone is at 3100 m depth in well WD-1a.     

Geochemical monitoring of the Krafla and Námafjall geothermal areas, N-Iceland

The Krafla and Námafjall high-temperature geothermal areas in N-Iceland have been exploited for steam production since the late and early 1970s, respectively. Power generation at Krafla was 30 MW until 1998, when it was increased to 60 MW. At Námafjall the steam has been utilized for operating a 3 MW back-pressure turbine unit, drying of diatomaceous earth and heating of fresh water for space heating. A total of 34 wells have been drilled at Krafla, of which 18 are producing at present. At Námafjall 12 wells have been drilled but only three are productive. The highest temperatures recorded downhole are 320 and 350 °C at Námafjall and Krafla, respectively. Geochemical monitoring in the two fields during the last 20–25 years has revealed decreases in the Cl concentrations in the water discharged from most of the wells that have been producing for more than 10 years. The cause is enhanced colder water recharge into the producing aquifers of these wells due to depressurization by fluid withdrawal from the geothermal reservoir. Such recharge is particularly pronounced in the central part of the Leirbotnar wellfield at Krafla but it is also extensive in the only producing well in the Hvíthólar wellfield. At Námafjall incursion of cold groundwater into the reservoir was particularly intense subsequent to the volcanic-rifting event in the area in 1977. Solute (quartz, Na/K, Na/K/Ca) geothermometry temperatures have decreased significantly in those wells where Cl concentrations have decreased but only to a limited extent in those wells which have remained constant in Cl. This indicates that the changes in the concentrations of the reactive components, on which these geothermometers are based, is largely the consequence of colder water recharge and not partial re-equilibration in the depressurization zone around wells where cooling of the fluid occurs in response to extensive boiling. Aqueous SO₄ concentrations increase as Cl concentrations decrease. Except for the hottest wells, which are low in SO₄, sulphate concentrations are controlled by anhydrite solubility. Increase in SO₄ concentrations is a reflection of cooling as anhydrite has retrograde solubility with respect to temperature. H₂S-temperatures are similar to the solute geothermometry temperatures for wells with a single feed. They are, on the other hand, higher, for wells with multiple feeds, if the feed zones have significantly different temperatures. H₂-temperatures are anomalously high for most wells due to the presence of equilibrium steam in the producing aquifers. The equilibrium steam fraction amounts to 0–2.2% by wt. of the aquifer fluid (0–47% by volume). CO₂ temperatures are anomalously high for some Krafla wells due to high flux of CO₂ from the magma intruded into the roots of the geothermal system during the 1975–1984 volcanic-rifting episode. During the early phase of this episode the Leirbotnar wells were the ones most affected. The new magma gas flux has migrated eastwards with time. Today some wells in the Sudurhlídar wellfield are the ones most affected whereas the Leirbotnar wells have recovered partly or fully. The depth level of producing aquifers in individual wells at Krafla and Námafjall has been evaluated by combining data on temperature and pressure logging and geothermometry results. The majority of wells at Krafla receive fluid from a single aquifer, or from 2–3 aquifers having similar temperature. The same applies to two of the three productive wells at Námafjall.     

A reconnaissance geochemical study of thermal waters of south and central Vietnam

Chemical and isotopic data of thermal springs and wells indicate that some thermal water circuits in central and south Vietnam can reach temperatures of geothermal interest (150–200°C) in zones of normal-to-slightly anomalous thermal gradients. The low gas content and the low CO₂ and H₂S concentrations suggest that there is no contribution from a magmatic source. The geothermometry results indicate that the geothermal resources in south and central Vietnam are of medium enthalpy. These results confirm those of previous geochemical surveys and indicate that the most promising geothermal sites in Vietnam are Le Thuy, south of Dong Hoi and Mo Duc near Quang Nghai.     

Research and development of geothermal energy production in Hungary

The basement of the Pannonian (Carpathian) basin is represented by Paleozoic metamorphic and Mesozoic dolomite and limestone formations. The Tertiary basin gradually subsided during the Alpine orogeny down to 6000 m and was filled by elastic sediments with several water horizons.A heat flow of 2.0 to 3.4 μcal/cm²s gives temperature gradients between 45 and 70 °C/km in the basin. At 2000 m depth the virgin rock temperature is between 110 and 150°C. 80 geothermal wells about 2000 m deep have shown the great geothermal potential of the basin.The main hot water reservoir is the Upper Pliocene (Pannonian) sandstone formation. Hot water is produced by wells from the blanket or sheet sand and sandstone, intercalated frequently by siltstone. Between a 100–300 m interval, 3 to 8 permeable layers are exploited resulting in 1–3 m³/min hot water at 80–99°C temperature.Wells at present are overflowing with shut-in pressures of 3–5 atm.The Pannonian basin is a conduction-dominated reservoir. Convection systems are negligible, hot igneous systems do not exist. The assessment of geothermal resources revealed that the content of the water-bearing rocks down to 3000 m amounts to 12,600 × 10¹⁸cal. In the Tertiary sediments 10,560 × 10¹⁸cal and in the Upper Pannonian, 1938 × 10¹⁸cal are stored. In the Upper Pannonian geothermal reservoir, below 1000 m, where the virgin rock temperature is between 70 and 140°C, the stored heat is 768 × 10⁸cal. A 10¹⁸ cal is equivalent to the combustion heat of 100 million tons of oil. The amount of recoverable geothermal energy from 768 × 10⁸cal is 7.42 × 10¹⁸cal, i.e. about 10,000 MW century, not considering reinjection.At present the Pannonian geothermal reservoir stores the greatest amount of identified heat which can be mobilized and used. Hungary has 496 geothermal wells with a nominal capacity of 428 m³/min, producing 1342 MW heat. 147 wells have an outflow temperature of more than 60°C producing 190 m³/min, that is, 845 MW. In 1974 290 MWyear of geothermal energy was utilized in agriculture, district heating and industry.     

Geochemistry of the surface and deep fluids of the Miravalles volcano geothermal system (Costa Rica)

The Miravalles high-temperature geothermal reservoir, located in the northwestern part of Costa Rica, is liquid-dominated. Reservoir temperatures generally range between 230 and 240 °C. The highest measured value is 255 °C. Bottom-hole measurements and solute geothermometry indicate that thermal conditions within the reservoir are very stable over time. The waters discharged from the wells have a neutral or slightly alkaline pH and are of the sodium-chloride type. Based on isotope data, the main recharge zone appears to be located on the northeastern side of the Guanacaste Cordillera. Several mixing trends have been identified between reservoir fluids and regional groundwaters. Gas discharges are dominated by CO₂, with minor amounts of H₂S and N₂. Relative N₂, Ar and He contents reveal a typical arc-type signature and significant inflow of meteoric-derived gases. Cl–SiO₂-enthalpy and δ¹⁸O–δ²H–Cl relationships suggest the existence of a maturation trend that is the result of both natural (i.e. direct drainage of deeper fluids) and anthropogenic causes (reinjection of Cl-rich waste waters). Acid fluids with SO₄-acidity (pH ranging between 2.4 and 3.7) have been encountered in three wells at the eastern border of the well field. Preliminary data assessment indicates two possible sources, either superficial H₂S oxidation or inflow of “immature” volcanic waters.     

The geothermal industry in Iceland

Direct (non-electrical) uses of geothermal energy in Iceland in 1984 amounted to 5517 GWh and the installed power was 889 MW_t, assuming 35°C discharge temperature. The bulk of this thermal power was for district heating, called hitaveita in Icelandic. In recent years this utilization has increased moderately. The installed geothermal electric power is currently 41 MW_e and is unlikely to change in the near future. Icelandic personnel have participated in many geothermal projects of the United Nations during the last 35 years. Contract work has been carried out by Icelandic consulting firms in several developing countries.     

Geology and fluid chemistry of the Fushime geothermal field, Kyushu, Japan

The Fushime geothermal field is located in a depression close to the coast line. The system is characterized by very high reservoir temperature (>350°C), and a high salinity production fluid. Geological analysis shows that the main reservoir in this field occurs in a fractured zone developed around a dacite intrusion located in the center of the field. High permeability zones recognized by drilling data are found to be associated with fault zones. One of these zones is clearly associated with a NW–SE trending andesite dike swarm which was encountered in some wells.Alteration in the system can be divided into four zones, in order of increasing temperature, based on calcium–magnesium aluminosilicate mineral assemblages: i.e., the smectite, transition, chlorite and epidote zones. The feed zone is located in the chlorite and epidote zones, which can be further divided into three sub-zones according to their potassium or sodium aluminosilicate mineralogy, from the center of the discharge zone: K-feldspar–quartz, sericite–quartz, and albite–chlorite zones.Chloride concentration of the sea-water is 19,800 mg/l, and Br/Cl mole ratio is 1.55. Based on geochemical information, the reservoir chloride concentration of this field ranges from 11,600 to 22,000 mg/kg. The Clres (Cl in reservoir), Br/Cl ratios and stable isotope data indicate that the Fushime geothermal fluid originated from sea-water and is diluted by ground water during its ascent. Some fluids produced from geothermal wells show low pH (about 4). It is thought that sulfide mineral (PbS, ZnS) precipitation during production produces this acidic fluid.