Sustainable development of the Kamojang geothermal field

Geothermal electricity production in Indonesia began with the operation of a 0.25 MW_e pilot project in Kamojang geothermal field, in 1978. Commercial operation started in 1983, with the commissioning of the 30 MW_e Unit-1 power plant. In 1987, an additional capacity of 110 MW_e was provided by the Unit-2 and Unit-3 power plants. The addition of the 60 MWe Unit-4 power plant in 2008 increased the total generating capacity to 200 MW_e. The 27 years of commercial operation have led to a slight decline in reservoir pressure and temperature within the active production sector. The most recent significant change in the field conditions and performance occurred following the 2008 increase in generating capacity from 140 to 200 MWe. The production decline of individual wells has been relatively low, at an average of 3%/yr. However, the increased rate of steam withdrawal might negatively affect long-term sustainability of energy production at Kamojang unless suitable field management strategies are implemented. In order to stabilize the steam flow, it has been necessary to drill about three make-up wells every 2–3 years. The unbalanced mass extraction, where less than 30% of the produced steam mass can be injected, is a serious concern for long-term reservoir management in Kamojang. The field operator (Pertamina) plans to increase the Kamojang generating capacity from 200 to 230 MWe (Unit 5) and optimize the long-term performance of the Kamojang geothermal resource. The response of the reservoir during the previous three decades is being used to guide reservoir development for the planned increase in production capacity.     

Evolution of the Wairakei geothermal reservoir during 50 years of production

The Wairakei geothermal field has been under production for more than 50 years. Exploration wells show that the high-temperature and very permeable, productive resource extends over about 12 km² within a greater area of about 25 km² that shows various effects of thermal activity. Up to 2006, 3 km³ of fluid and 2750 PJ of energy had been extracted at an average rate of 5250 t/h and enthalpy of 1130 kJ/kg. Significant production started in 1955 and up to 1978 there was no injection of cooled geothermal fluids. During the first decade of operation a pressure drawdown of up to 20 bars (2 MPa) developed and spread evenly across the reservoir, even though fluid extraction was focused within an area of 1 km² close to the northeastern field boundary. This pressure reduction resulted in widespread boiling and formation of segregated steam zones at the top of the reservoir together with inflow of cooler fluids into its northeastern part via the original natural outflow channels. From 1975 to 1997 pressures in the deep liquid reservoir stabilized at 23–25 bars (2.3–2.5 MPa) below the original pressure, with little change up to the time injection commenced in 1998. This natural pressure support indicates that prior to injection there was substantial recharge, 80% of which is assessed as high-temperature deep inflow. Since 1998 about 30% of the extracted fluids have been injected and reservoir pressures have increased by 3–4 bars (0.3–0.4 MPa). To date, significant returns of injected fluids have not been detected in the production areas. Over the 50 years of operation, temperatures in the main production areas have declined from 250 to 220 °C while deeper production zones toward the western boundary of the reservoir have remained at about 250 °C. A series of deeper makeup wells to maintain future production have been drilled in the high-temperature recharge area. An increasing fraction of injection, both in-field and out-field is planned over the next few years.     

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.     

Results of a 3D seismic survey at the Travale (Italy) test site

In the last 15 years geothermal exploration in Tuscany, Italy, has addressed deep reservoirs (depth ≥ 3000 m), hosted within complex geological systems, such as metamorphic formations and/or intrusive bodies. Reservoir productivity is linked to fractured and permeable zones that are rather confined and not uniformly distributed. In this context, the seismic methods represent one of the most reliable geophysical techniques for locating potential drilling targets. A 3D seismic survey has been acquired at the Travale test site, and its results have been used to develop a geological and structural model of the site, and to identify and characterize fractured zones inside the deep geothermal reservoir. A correlation between a high-amplitude reflector (H marker) and fractured contact-metamorphic rocks has been highlighted. More than 70% of the total geothermal fluid production at the Travale area comes from this seismic marker.     

An estimate of the resource potential of New Zealand geothermal fields for power generation

The basic similarity between most of the New Zealand geothermal fields suggests that the exploited fields of Wairakei and Broadlands can be used as indicators of the potential of other fields as resources for steam for power production. Assuming adequate permeability will be obtained in fields yet to be tested, the two parameters controlling this potential are areal extent (as defined by resistivity survey) and temperature at depth. As most field temperatures are bracketed by Wairakei (270°C maximum) and Broadlands (310°C maximum), field potential per unit area should also be bracketed by the field potentials per unit area of these two fields, i.e. Wairakei at 10–11 MWe/km² and Broadlands at 13–14 MWe/km².Based upon our present knowledge of the fields in question we may thus assess their proven, inferred and speculative reserves. Our totals for all fields of 450 MWe proven, 750 MWe inferred and 1300 MWe speculative suggests that New Zealand has some 1300–2500 MWe available from its geothermal resources should it desire to exploit these for electrical power.These figures can only be confirmed and improved by drilling and ultimately by exploitation. The most promising tool for a full assessment of a field potential, the reservoir model, can only really be set up once the field has been exploited sufficiently to have been disturbed. In future cases this may only be the case once a power station has been established and has been operating for some time.     

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.     

Fumarolic gas chemistry at Wairakei,New Zealand, 1936–1998

The Wairakei geothermal field fumarolic discharges are at their greatest intensity from the Karapiti Thermal Area. This part of the geothermal field contains numerous steam-dominated features in an area of approximately 1 km². Since 1952 there have been many changes to the surface features and thermal activity at Karapiti related to the development-induced pressure drawdown over most of the field. A greatly expanded steam cap fed by a large low-pressure steam zone in the Wairakei reservoir has replaced the hot chloride water originally underlying Karapiti. There have been intermittent chemical surveys of the steam vents at Karapiti since 1951, with major chemical surveys undertaken in 1961 and 1990. In 1990, the concentrations of CO₂ were found to be about 200 mmol/100 mol H₂O, double the 1961 values. Of particular interest is the change between 1936 and 1987 in gas chemistry of the main Karapiti feature, the Karapiti Blowhole (F712), which follows the change in heatflow from the Karapiti Thermal Area. Since 1990, gas concentrations appear to be dropping to low, pre-development levels, most likely due to the decreasing pressures in the lower pressure steam zone. Underground processes leading to a high gas content in a large fumarole formed in 1967 and other fumaroles in different parts of the Wairakei field are discussed.     

Geothermal resources of the Beijing area, China

Hot water resources were discovered in 1970 at a fairly shallow depth below the city of Beijing. The total areal extent of the geothermal field is presently estimated at more than 100 km². The two known thermal aquifers are composed of fractured dolomites and the temperature of the aquifers ranges from 53 to 80°C. Based on the production-drawdown history of the Beijing geothermal field, for the period 1971–1981, the unit step response of the reservoir is obtained. Parameters of a simple lumped two-capacitor model, matched with the unit step response, furnish some information on dimensions and overall potential of the Beijing reservoir.     

Overview of the Wayang Windu geothermal field,West Java,Indonesia

The Wayang Windu geothermal field, West Java, Indonesia, is interpreted to be transitional between vapour-dominated and liquid-dominated conditions with four coalesced fluid upwelling centres that generally become younger and more liquid-dominated towards the south. Two of these centres are associated with the large Gunung Malabar andesite stratovolcano and the other two with the smaller aligned Gunung Wayang and Gunung Windu andesitic volcanoes to the south. The overall potential resource area is of the order of 40 km². Deep wells encounter a deep liquid reservoir whose top, which ranges from 0 to 400 m above sea level (m asl) becomes progressively deeper toward the south. As pressure versus elevation conditions are the same throughout the deep liquid reservoir it is likely to be contiguous. This liquid-dominated reservoir is overlain by three separate vapour-dominated reservoirs. The northernmost is the largest as it is coalesced over two separate fluid upwelling centres. Its low gas content, size, prolonged productivity and isobaric for elevation nature, preclude it from being a parasitic steam zone. Mineralogical relationships demonstrate that this vapour zone was originally liquid-dominated with a deep water level as high as 1700 m asl. Subsequent boil off may reflect low recharge rates due to hydrological isolation at depth. To the south, the vapour-dominated reservoirs decrease in thickness and are characterized by progressively higher pressures, temperatures and gas contents. These changes suggest that the southernmost vapour-dominated zone is the youngest and that these zones become increasing older to the north.     

Preliminary geothermal model of the travale field, Italy

Based on geological and geothermal knowledge of the Travale geothermal field, a mathematical model is proposed for the heat transfer from the top of the reservoir to the soil surface.Consistency between observed and calculated temperatures demonstrates that the heat is transferred by conduction and that the established temperature field depends essentially on the temperature at the top of the reservoir and its slope.     

Exploration of Lahendong geothermal field in North Sulawesi, Indonesia

This paper describes the progress made in developing the geothermal resources at Lahendong, North Sulawesi, Indonesia for utilization in power generation. Exploration of the whole region included a geophysical survey undertaken exclusively by the Volcanological Survey of Indonesia (VSI). A temperature survey at various depths was conducted through gradient boreholes. The results show that the area of anomalous temperature corresponds to the area of low resistivity revealed by the seismic survey. Two shallow exploratory boreholes (300–400 m) drilled by VSI confirmed the existence of the resources. The deep reservoir in Lahendong field extends over an area of 10 km²; the upper parts of the reservoir are presumed to be water dominated (temperatures in excess of 200°C) and to overlie a zone of hot chloride water at an undetermined depth. The potential of Lahendong field is estimated to about 90 MW.In Pelita IV (1984–1989), the fourth 5-year plan, the State Electricity Public Corporation plans to construct a 30 MW geothermal power-plant in the Lahendong field.     

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.     

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.     

Tests of electric and electromagnetic methods in the travale geothermal field

Within the framework of an EEC project involving ten European laboratories, research on the application of several electric and electromagnetic methods to a geothermal field (Travale, Tuscany), has been undertaken by the B.R.G.M. The objective was to refine the conceptual model of the Travale field and, therefore, to describe the morphology of the basement (down to 2 km depth) and of the Rhaetian reservoir covered by impermeable series.The method best suited to this type of prospection appeared to be electrical dipole — dipole profiling, combined with a 2-D interpretation. Contrasts at more than 2 km depth (500 m long dipoles) could be seen and compared to the depths measured in the boreholes. The EM Melos method (Syscal equipment) should be improved (lower frequencies) to increase the depth penetration. It is, however, a good complementary method for the surface layers. An attempt at a computational interpretation of the self potential profiles gave promising results. To make full advantage of the bipole — dipole measurements efforts should be devoted to their computational interpretation.     

Inverse modeling and forecasting for the exploitation of the Pauzhetsky geothermal field,Kamchatka, Russia

A three-dimensional numerical model of the Pauzhetsky geothermal field has been developed based on a conceptual hydrogeological model of the system. It extends over a 13.6-km² area and includes three layers: (1) a base layer with inflow; (2) a geothermal reservoir; and (3) an upper layer with discharge and recharge/infiltration areas. Using the computer program iTOUGH2 [Finsterle, S., 2004. Multiphase inverse modeling: review and iTOUGH2 applications. Vadose Zone J. 3, 747–762], the model is calibrated to a total of 13,675 calibration points, combining natural-state and 1960–2006 exploitation data. The principal model parameters identified and estimated by inverse modeling include the fracture permeability and fracture porosity of the geothermal reservoir, the initial natural upflow rate, the base-layer porosity, and the permeabilities of the infiltration zones. Heat and mass balances derived from the calibrated model helped identify the sources of the geothermal reserves in the field. With the addition of five make-up wells, simulation forecasts for the 2007–2032 period predict a sustainable average steam production of 29 kg/s, which is sufficient to maintain the generation of 6.8 MWe at the Pauzhetsky power plant.     

Electrical conductivity studies in the Travale geothermal field, Italy

Magnetotelluric and geomagnetic depth soundings have been carried out in the area of the Travale high enthalpy geothermal field (central Tuscany, Italy) in 1980 and 1981 to study the distribution of electrical conductivity in the geothermal anomaly and the crust beneath. Within this project the possible contributions of electromagnetic investigations to geothermal research were to be tested and a geothermal model of the Travale area was to be developed. The time-varying electric and magnetic fields have been recorded in a broad period range from 6–10,000 s, mainly on two profiles, the one parallel, the other perpendicular to the Travale graben. Strong lateral variations of apparent resistivities have been observed. Up to periods of 50–100 s the Travale graben is the dominating 2-D structure, but for longer periods of investigation the three-dimensionality of electrical conductivity structures has to be considered. The apparent resistivities inside the geothermal anomaly are extremely low, reaching not more than 50 ohm · m, even in the lower crust, but they increase to 100–300 ohm · m north of the geothermal field. Total conductance also indicates the geothermal field as a local conductivity anomaly, whereas further to the north the poorly conducting “barrier” has been confirmed. The cause of the high conductivity structures inside the geothermal area is to be seen in a highly fractured basement within this zone, allowing upward movement of hydrothermal fluids.     

System dynamics modelling of spring behaviour in the Orakeikorako geothermal field,New Zealand

System dynamics software STELLA is used to obtain mass and thermal balances of a spring in the Orakeikorako geothermal field, New Zealand, based on field measurements of water level, barometric pressure, rainfall and spring temperature. The model identifies the interactions of the principal influences on spring behaviour of rainfall, groundwater, geothermal steam and barometric pressure. The geothermal steam inflow estimated from the model, of about 0.022 kg/s, confirms the existence of a weak hydraulic connection with a deeper geothermal reservoir.     

Hydrogeochemical exploration of geothermal prospects in the Tecuamburro Volcano region, Guatemala

Chemical and isotopic analyses of thermal and nonthermal waters and of gases from springs and fumaroles are used to evaluate the geothermal potential of the Tecuamburro Volcano region, Guatemala. Chemically distinct geothermal surface manifestations generally occur in separate hydrogeologic areas within this 400 km² region: low-pressure fumaroles with temperatures near local boiling occur at 1470 m elevation in a sulfur mine near the summit of Tecuamburro Volcano; non-boiling acid-sulfate hot springs and mud pots are restricted to the Laguna Ixpaco area, about 5 km NNW of the sulfur mine and 350–400 m lower in elevation; steam-heated and thermal-meteoric waters are found on the flanks of Tecuamburro Volcano and several kilometers to the north in the andesitic highland, where the Infernitos fumarole (97°C at 1180 m) is the primary feature; neutral-chloride hot springs discharge along Rio Los Esclavos, principally near Colmenares at 490 m elevation, about 8–10 km SE of Infernitos. Maximum geothermometer temperatures calculated from Colmenares neutral-chloride spring compositions are 180°C, whereas maximum subsurface temperatures based on Laguna Ixpaco gas compositions are 310°C. An exploration core hole drilled to a depth of 808 m about 0.3 km south of Laguna Ixpaco had a bottom-hole temperature of 238°C but did not produce sufficient fluids to confirm or chemically characterize a geothermal reservoir. Hydrogeochemical data combined with regional geologic interpretations indicate that there are probably two hydrothermal-convection systems, which are separated by a major NW-trending structural boundary, the Ixpaco fault. One system with reservoir temperatures near 300°C lies beneath Tecuamburro Volcano and consists of a large vapor zone that feeds steam to the Laguna Ixpaco area, with underlying hot water that flows laterally to feed a small group of warm, chloriderich springs SE of Tecuamburro Volcano. The other system is located beneath the Infernitos area in the andesitic highland and consists of a lower-temperature (150–190°C) reservoir with a large natural discharge that feeds the Colmenares hot springs.     

Temperature evaluation of the Bugok geothermal system, South Korea

Using a variety of chemical geothermometers and statistical analysis, we estimate the temperature of a possible deeper geothermal reservoir at Bugok, Southern Korea. Shallow thermal aquifers (down to about 400 m depth) are under exploitation in this area; the temperatures (up to 78 °C) of the produced fluids are the highest found in South Korea. Based on hydrochemical data and occurrence, the groundwaters at Bugok can be classified under three groups: Na-SO₄ thermal groundwaters (CTGW) occurring in the central (about 0.24 km²) part of the area; Ca-HCO₃ cold groundwater (SCGW) found in shallow peripheral parts of the CTGW; the intermediate-type groundwater (STGW). The CTGW type is typical of the Bugok thermal waters; they have the highest discharge temperatures and contain very high concentrations of Na (75.1–101.0 mg/L), K (2.9–6.9 mg/L) and SiO₂ (62.0–84.5 mg/L) and are rich in sulfates.The major ion composition of the CTGW suggests that these waters are in partial equilibrium with rocks at depth. The application of various alkali-ion geothermometers yields temperature estimates in the 88–198 °C range for the thermal reservoir. Multiple-mineral equilibrium calculations indicate a similar but narrower temperature range (from about 100 to 155 °C). These estimates for CTGW are significantly higher than the measured discharge temperatures. Considering the heat losses occurring during the ascent of the waters, one can infer the presence of a deeper (around 1.8 km) thermal reservoir in the Bugok area that could be developed for district heating or other direct applications of geothermal heat.