Fluid-inclusion evidence for past temperature fluctuations in the Kilauea East Rift Zone geothermal area, Hawaii

Heating and freezing data were obtained for fluid inclusions in hydrothermal quartz, calcite, and anhydrite from several depths in three scientific observation holes drilled along the lower East Rift Zone of Kilauea volcano, Hawaii. Compositions of the inclusion fluids range from dilute meteoric water to highly modified sea water concentrated by boiling. Comparison of measured drill-hole temperatures with fluid-inclusion homogenization-temperature (T_h) data indicates that only about 15% of the fluid inclusions could have formed under the present thermal conditions. The majority of fluid inclusions studied must have formed during one or more times in the past when temperatures fluctuated in response to the emplacement of nearby dikes and their subsequent cooling. The fluid-inclusion data indicate that past temperatures in SOH-4 well were as much as 64°C hotter than present temperatures between 1000 and 1500 m depth and they were a maximum of 68°C cooler than present temperatures below 1500 m depth. Similarly, the data show that past temperatures near the bottoms of SOH-1 and SOH-2 wells were up to 45 and 59°C, respectively, cooler than the present thermal conditions; however, the remainder of fluid-inclusion T_h values for these two drill holes suggest that the temperatures of the trapped waters were nearly the same as the present temperatures at these slightly shallower depths. Several hydrothermal minerals (erionite, mordenite, truscottite, smectite, chlorite-smectite, chalcedony, anhydrite, and hematite), occurring in the drill holes at higher temperatures than they are found in geothermal drill holes of Iceland or other geothermal areas, provide additional evidence for a recent heating trend.     

Towards a de-carbonized energy system in north-eastern Morocco: Prospective geothermal resource

Geothermal data has been indicating promising potentialities in the north-eastern Morocco. This paper presents new temperature data, recently recorded in water boreholes located in the Berkane and Oujda areas. Generally, the observed temperature gradients are rather high. One hole near Berkane, revealed an average geothermal gradient of more than 110 °C/km at depths greater than 300 m. This result confirms the geothermal gradient estimated in a mining borehole located about 30 km west of the Berkane borehole, in which water temperature of 96 °C is reached at a depth of about 700 m. Such a high geothermal gradient, exceeding by far the ones already determined for northeastern Morocco, could act as a stimulus to programs aimed at the geothermal exploitation of high temperature aquifers.     

Hydrogeochemistry and geothermometry of Changal thermal springs,Zagros region,Iran

This study addresses the hydrogeochemistry of thermal springs that emerge from the Asmari limestone in a gorge at Changal Anticline in the vicinity of the Salman-Farsi dam. The Changal thermal springs vary in temperature between 28 and 40 °C. Chemical and isotopic compositions of the thermal waters suggest two distinct hydrogeological systems: a deep, moderate-temperature (∼40 °C) geothermal system recharged by deeply circulating meteoric waters, and a shallow cold aquifer system related to local groundwater. The source geothermal fluid temperature was calculated using different geothermometers and mineral saturation indexes. Based on chemical and isotopic data, it is hypothesized that: (1) mixing occurs between the ascending geothermal water and shallow cold water; (2) the resulting thermal waters reaching surface are a mixture of 80% local, shallow meteoric water and 20% geothermal water; and (3) the circulation depth of the meteoric water is about 1500 m. The thermal reservoir temperature is estimated to be between 70 and 80 °C according to calculations using different geothermometers and computation of saturation indices for different solid phases.     

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.     

Investigations of deep resistivity structures at the Wairakei geothermal field

The Wairakei geothermal field was the proving ground for the use of electrical resistivity methods for geothermal exploration. At this site it was first demonstrated that a large contrast in resistivity existed between geothermal ground and the cold surroundings. Within the top 500 m of the geothermal field, low-resistivity (5–10 Ωm) reflects the effects of both the hot saline water in the pore spaces and the conductive rock-matrix. The first surveys at Wairakei used a Wenner array (a ∼550 m) to measure the resistivity values along tracks throughout the field; contour maps of the resistivities were used to estimate the lateral extent of the geothermal waters at a few hundred metres depth. In the late 1960s the Wenner array was superseded by the Schlumberger array (AB/2 = 500 m and 1000 m), which enabled deeper penetration and better definition of the extent of the geothermal waters. These early surveys showed that the bounds of the geothermal waters were often sharp, leading to the concept that a ‘resistivity boundary’ could be defined for New Zealand's liquid-dominated geothermal fields. As new methods of measuring electrical structure with greater precision became available, Wairakei was often chosen as the testing ground.     

Recent ground subsidence at Crown Road,Tauhara and its probable causes

A localised ground subsidence anomaly at Crown Road, Taupo, within the Tauhara field of the Wairakei–Tauhara geothermal system, has been subjected to intense scrutiny because of its relatively recent onset and proximity to urban areas. Over a period of 20 years a maximum of 0.63 m of subsidence has accumulated. Uncertainties regarding its cause remain, but the evidence now strongly favours a relatively shallow (about 50 m depth) origin, compared with other geothermal subsidence bowls at Wairakei, Tauhara and Ohaaki. Declining water levels in a shallow boiling aquifer are considered to be the principal driving mechanism at Crown Road. The source of the subsidence is an anomalously compressible formation of intensely altered ignimbrite found at the base of a buried hydrothermal eruption deposit. This formation is dominated by soft kaolinite and smectite-illite clays of high plasticity and water content, resulting from alteration of highly vesiculated pumice, and is capped by a thin hardpan of silicified pyroclastic material, characterised by vuggy macro-porosity, at about 33 m depth. During initiation of the subsidence event, this hardpan may have failed in shear mode around the edges of a buried eruption crater, allowing the overburden to fully load the underlying compressible clays.     

Gravity changes in the Tauhara sector of the Wairakei–Tauhara geothermal field,New Zealand

Five microgravity surveys, done between 1972 and 2006, show that in the northern part of the Tauhara geothermal field there were large gravity decreases prior to 1985 associated with the expansion of steam zones resulting from pressure drawdown caused by fluid extraction at Wairakei. Since 1985 there have been gravity increases of up to 240 μgal in the northern part of Tauhara, corresponding to a mass increase of about 20 Mt. The gravity increases are centred near the unused deep well TH4, and are inferred to result mainly from resaturation of a deep steam zone due to a downflow of water in the well. We suggest that the water entered the well from a confined groundwater aquifer at a known casing break at 393 m depth and exited in the region of slotted casing at about 900–1000 m depth causing displacement of single-phase liquid upwards into the overlying steam zone. The average downflow rate is estimated to be about 110 t/h (30 kg/s); however, no downhole measurements in the well have been possible due to casing breaks. Simple modelling of the gravity data suggests the region of resaturation had the form of a cone of impression 150–250 m high and extending laterally for 1–2 km. Since 1985, gravity changes in the central and southern parts of the Tauhara field have been less than 50 μgal, indicating little net mass loss (<2 Mt), and hence little effect in this area from the continuing production at Wairakei. The subsidence centred near Crown Road has been attributed to compaction of a thin, elliptical lens of porous, thermally-altered volcanic deposits at shallow depth as a result of a water level decline in the near-surface, steam-heated groundwater aquifer. Gravity data (1994 onwards) at a point near the centre of the subsidence bowl show that, despite ground subsidence of about 0.55 m, there have been no significant gravity changes. One explanation for the absence of gravity changes is that the water lost from the near-surface aquifer has drained downwards increasing the saturation in part of a deeper, partly saturated layer.     

Experimental study of the influence of collector height on the steady state performance of a passive solar air heater

Passive solar air heaters, such as solar chimneys and Trombe Walls, rely on solar-induced buoyancy-driven (natural) convection to produce the flow of air. Although buoyancy-driven convection is well understood for a single vertical plate, buoyancy-driven convection in an asymmetrically-heated channel is more problematic, and in particular, the effects of the channel height on the flow rate and heat transfer. This paper reports on experiments on test rigs resembling lightweight passive solar air-heating collectors. The test rigs were of heights 0.5, 1.0 and 2.0 m, with adjustable channel depths (20-150 mm) and heat inputs (up to 1000 W/m²). Measurements were made of the air, plate and cover temperatures, and air velocities. Results are presented as dimensionless correlations of mass flow (as Reynolds number) and efficiency against heat input (as Rayleigh number), channel depth and height. Thermal efficiency is shown to be a function of the heat input and the system height, but not of the channel depth; mass flow is shown to be a dependent on all three parameters.     

Development program of hot dry rock geothermal resource in the Yangbajing Basin of China

Geothermal energy from hot dry rock (HDR), considered an almost inexhaustible source of “green” energy, was first developed and tested in the 1970s, leading to installations in America, Japan, Britain, France and other countries. In the present work, a liquating rock mass at a depth of 5-15 km in the Tibet Yangbajing region in China was subjected to detailed analysis. The temperature distribution of the geothermal field in the region was determined by the finite element method. The results estimate that the HDR geothermal resource of the Yangbajing region is 5.4 × 10⁹ MW a, representing a huge potential source of HDR geothermal energy for China. Based on detailed research into the continental dynamics of the environment forming the HDR geothermal field of Tibet, along with the tectonic characteristics of the southern slope of Tanggula Mountain and the Dangxiong-Yangbajing Basin, and the magnitude and orientation of the in situ stresses in the region, the design of an arrangement for extracting these HDR geothermal resources is proposed: taking the fault zone nearest the high-temperature liquating rock region as the location of an artificial reservoir, a vertical injection well could be drilled at a low point on the downdip side of the fault, and two dipping production wells drilled higher up. In this way, an artificial reservoir 3 × 10¹¹ m³ in volume would be created: 360 times the volume of the HDR geothermal reservoir in Cornwall, UK, which uses hydrofracturing. An investigation of the reservoir features, including seepage analysis of the heat exchange area, project implementation and investment analysis, indicates that a 10⁴ MW capacity power station with a projected operating life of approximately 100 years could be constructed. An analysis of a geothermal extraction system comprising one injection well and two production wells suggest that a power station of 1000 MW installed capacity could be constructed initially to provide electricity production of 8.64 × 10⁹ kWh per year.     

Geothermal development in Romania

Exploration for geothermal resources began in Romania in the early 1960s, based on a detailed geological exploration program for hydrocarbon resources that had a capacious budget and enabled the identification of eight geothermal areas. Over 200 wells drilled to depths between 800 and 3500 m have indicated the presence of low-enthalpy geothermal resources (40–120 °C). Completion and experimental production from over 100 wells during the past 25 years has led to the evaluation of the exploitable heat resources of the geothermal reservoirs. The proven reserves, with the wells that have already been drilled, amount to about 200,000 TJ for 20 years. The main geothermal systems discovered on Romanian territory are in porous permeable formations such as sandstones and siltstones (Western Plain and the Olt Valley) or in fractured carbonate formations (Oradea, Bors, and north of Bucharest). The total thermal capacity of the existing wells is about 480 MW_t (for a reference temperature of 25 °C). Only 152 MW_t of this potential is currently being exploited, from 96 wells (35 of which are used for health and recreational bathing), producing hot water in the temperature range 45–115 °C. In 2002 the annual energy utilisation from these wells was about 2900 TJ, with a capacity factor of 0.6. More than 80% of the wells are artesian producers, 18 wells require anti-scaling chemical treatment and six are reinjection wells. During the period 1995–2002, 15 exploration-production geothermal wells were drilled and completed, two of which were dry holes. Drilling was financed by the geological exploration fund of the State Budget, to depths varying between 1500 and 3500 m. Progress in the direct utilisation sector of geothermal resources has been extremely slow because of the difficulties encountered during the transition period from a centrally planned to a free-market economy; geothermal production is at present far below the level that could be expected from its assessed potential, with geothermal operations lagging behind in technology. The main obstacle to geothermal development in Romania is the lack of domestic investment capital. In order to stimulate the interest of potential investors from developed countries and to comply with the requirements of the large international banks, an adequate legal and institutional framework has been created, adapted to a market-oriented economy.     

Controls on the Karaha–Telaga Bodas geothermal reservoir,Indonesia

Karaha–Telaga Bodas is a partially vapor-dominated, fracture-controlled geothermal system located adjacent to Galunggung Volcano in western Java, Indonesia. The geothermal system consists of: (1) a caprock, ranging from several hundred to 1600 m in thickness, and characterized by a steep, conductive temperature gradient and low permeability; (2) an underlying vapor-dominated zone that extends below sea level; and (3) a deep liquid-dominated zone with measured temperatures up to 353 °C. Heat is provided by a tabular granodiorite stock encountered at about 3 km depth. A structural analysis of the geothermal system shows that the effective base of the reservoir is controlled either by the boundary between brittle and ductile deformational regimes or by the closure and collapse of fractures within volcanic rocks located above the brittle/ductile transition. The base of the caprock is determined by the distribution of initially low-permeability lithologies above the reservoir; the extent of pervasive clay alteration that has significantly reduced primary rock permeabilities; the distribution of secondary minerals deposited by descending waters; and, locally, by a downward change from a strike-slip to an extensional stress regime. Fluid-producing zones are controlled by both matrix and fracture permeabilities. High matrix permeabilities are associated with lacustrine, pyroclastic, and epiclastic deposits. Productive fractures are those showing the greatest tendency to slip and dilate under the present-day stress conditions. Although the reservoir appears to be in pressure communication across its length, fluid, and gas chemistries vary laterally, suggesting the presence of isolated convection cells.     

Management of the Balcova–Narlidere geothermal reservoir,Turkey

The 2000–2005 management and field monitoring procedures at the Balcova–Narlidere geothermal field, Turkey are described. During that period, fluid production increased from 140 to 300 kg/s and the living space being heated grew from 0.64 to 1.6 million m². The shallow (depth <160 m) injection done between 1996 and 2002 cooled the fluids being produced; the hydraulic connection between shallow production and injection wells was confirmed by tracer tests. Two deep injection wells were drilled to mitigate the problem and to increase injection capacity. Because net fluid extraction was reduced, reservoir pressure drawdown was controlled. Wells drilled after 2000 indicated that the eastern portion of the field had greater potential and yielded higher temperature fluids. After testing and establishing well flow performance, pump capacities were matched to production well capacities. Mineral scaling in wells and surface installations was brought under control reducing the annual cost of inhibitors by about US$100,000. Since all production and injection wells are located near the Agamemnon fault zone and because the capacity of the district heating system is being continuously increased, there is the risk of thermal breakthrough in the production wells.     

Geothermal energy in Turkey: 2008 update

Geological studies indicate that the most important geothermal systems of western Turkey are located in the major grabens of the Menderes Metamorphic Massif, while those that are associated with local volcanism are more common in the central and eastern parts of the country. The present (2008) installed geothermal power generation capacity in Turkey is about 32.65 MWe, while that of direct use projects is around 795 MWt. Eleven major, high-to-medium enthalpy fields in western part of the country have 570 MWe of proven, 905 MWe of probable and 1389 MWe of possible geothermal reserves for power generation. In spite of the complex legal issues related to the development of Turkey's geothermal resources, their use is expected to increase in the future, particularly for electricity generation and for greenhouse heating.     

Fluid-inclusion evidence for previous higher temperatures in the miravalles geothermal field, Costa Rica

Heating and freezing data were obtained for liquid-rich secondary fluid inclusions in magmatic quartz, hydrothermal calcite and hydrothermal quartz crystals from 19 sampled depths in eight production drill holes (PGM-1, 2, 3, 5, 10, 11, 12 and 15) of the Miravalles geothermal field in northwestern Costa Rica. Homogenization temperatures for 386 fluid inclusions range from near the present measured temperatures to as much as 70°C higher than the maximum measured well temperature of about 240°C. Melting-point temperature measurements for 76 fluid inclusions suggest a calculated salinity range of about 0.2–1.9 wt% NaCl equivalent. Calculated salinities as high as 3.1–4.0 wt% NaCl equivalent for 20 fluid inclusions from the lower part of drill hole PGM-15 (the deepest drill hole) indicate that higher salinity water probably was present in the deeper part of the Miravalles geothermal field at the time these fluid inclusions were formed.     

Update on subsidence at the Wairakei–Tauhara geothermal system,New Zealand

The total subsidence at the Wairakei field as a result of 50 years of geothermal fluid extraction is 15 ± 0.5 m. Subsidence rates in the center of the subsidence bowl have decreased from over 450 mm/year during the 1970s to 80–90 mm/year during 2000–2007. The location of the bowl, adjacent to the original liquid outflow zone of the field, has not changed significantly. Subsidence at the Tauhara field due to Wairakei production was not as well documented in the early years but appeared later and has been less intense than at Wairakei. Total subsidence of 2.6 ± 0.5 m has also occurred close to the original liquid outflow zone of this field, and maximum subsidence rates in this area today are in the 80–100 mm/year range. In the western part of the Wairakei field, near the area of hot upflow, subsidence rates have approximately doubled during the last 20 years to 30–50 mm/year. This increase appears to be have been caused by declining pressure in the underlying steam zone in this area, which is tapped by some production wells. At Tauhara field, two areas of subsidence have developed since the 1990s with rates of 50–65 mm/year. Although less well-determined, this subsidence may also be caused by declining pressure in shallow steam zones. The cause of the main subsidence bowls in the Wairakei–Tauhara geothermal system is locally high-compressibility rocks within the Huka Falls Formation (HFF), which are predominantly lake sediments and an intervening layer of pumice breccia. At Wairakei, casing deformation suggests the greatest compaction is at 150–200 m depth. The cause of the large compressibility is inferred to be higher clay content in the HFF due to intense hydrothermal alteration close to the natural fluid discharge areas. Future subsidence is predicted to add an additional 2–4 m to the Wairakei bowl, and 1–2 m elsewhere, but these estimates depend on the assumed production-injection scenarios.     

A model for the sulphur springs geothermal field St Lucia

A model to explain the behaviour of the Sulphur Springs geothermal field has been derived from downhole temperature records in the exploration boreholes. The model incorporates a main reservoir at 1 – 1.5 km depth, intersected by steeply inclined fissures which carry steam and gas to the well bores, and to the natural fumaroles. A substantial decline in the gas content of the steam could have serious consequences where the fissures are utilised as conduits between the boreholes and the deep reservoir. Further development of the field should concentrate on the fissures around 300 m or on the reservoir itself around 1000 – 1500 m.     

Modeling contribution to risk assessment of thermal production power for geothermal reservoirs

We analyze the likelihood of success for heat production strategies in a sandstone reservoir in the north-eastern German basin in a depth of about 2 km by simulating both double and single well configurations. For this test case study we use an exploited oil and gas field. We combine seismic interpretation, numerical modeling, and stochastic estimation of rock properties to predict the transient temperature and pressure variations and their uncertainties in a geothermal reservoir. We demonstrate the essential necessity in geothermal reservoir modeling to account for heterogeneity of rock properties. We use 3D seismic data and stratigraphy data from about 100 wells at 1500 m – 2500 m depth for setting up a 3D stratigraphic model. Rock properties are assigned to this model by a Monte Carlo approach using Sequential Gaussian Simulation. Using 3D inversion of temperature data obtained in the wells we estimate a specific heat flow of 77.7 mW m⁻² ± 1.2 mW m⁻² at 6 km depth, in agreement with a temperature of 87.1 °C ± 1.8 K in the Rhaetian sandstone target layer at a depth of ∼2 km. For different types of potential geothermal well installations inside the Rhaetian sandstone layer the probability of success is just 1.6%.     

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 CO₂ 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 × 10³ 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.     

Utilization of existing deep geological wells for acquisitions of geothermal energy

The aim of this work is to assess the possibility and usefulness of accessing geothermal energy from the existing production well, Jachowka K-2. Discussions of both, a heat flow transferred between a deposit and a heat carrier and a heat flow permeated through the barrier are presented. A computational model, was designed to determine the volume of a gained geothermal heat flux with the use of a double-pipe geothermal heat exchanger with the dead centre [12]. Lastly, the article there are the results of calculations of available heat flux in the investigated well at the depth of L=3950 m are analyzed.     

The performance of miniature metallic PEM fuel cells

A prototype of metallic PEM fuel cell with thin stainless steel bipolar plates was tested for their potential applications in portable electronic products. The flow field pattern was grown from the stainless steel plates by the electroforming process. The main flow channel has the dimensions of 300 μm (width) × 300 μm (depth). The dimensions of the micro-features were 100 μm width × 50 μm depth and 50 μm width × 50 μm depth. The material of the electroformed flow field pattern is nickel. A prototype of a single cell with total thickness of 2.6 mm, overall reaction area of 4 cm² and bipolar plate area of 16 cm² was assembled for this study. In order to improve its corrosion resistance, the bipolar plates were coated with 5 μm thick of multi-layered corrosion resistant material.