High-enthalpy Systems Research Articles

Characterization of Geochemical and Isotopic Profiles in the Southern Zone Geothermal Systems of Mount Seulawah Agam, Aceh Province, Indonesia

The Seulawah Agam geothermal area exhibits significant potential as a source of energy for power generation, with an estimated capacity of 130 MW. Geological and geochemical investigations indicate that the Seulawah Agam geothermal system is part of the extensive Sumatra Fault. Analysis of the geochemical composition of geothermal water at the South Zone manifestation location of Mount Seulawah Agam, Aceh Province-Indonesia, involves examining cation (K+, Na+, Ca2+, and Mg2+), anion (Cl-, HCO3-, and SO42-), and isotope (δD and δ18O) contents. This data aids in estimating reservoir temperatures using geothermometer equations. Surface characteristics of the South Zone manifestation reveal neutral to alkaline pH values (6.02 to 8.68), relative temperatures (29.97 to 42.57 ºC), conductivity (49.8 to 100.7 mV), and TDS (Total Dissolved Solids) ranging from 352.6 to 497.0 mg/L. The dominant water composition is sodium–calcium–bicarbonate (Ca–Na–HCO3), indicating a bicarbonate water type. Average temperature depths in the South Zone manifestation of Mount Seulawah Agam are estimated as follows: Alue Ie Seu’um around 288.84 ± 2.19 ºC, Alue Ie Masam around 304.17 ± 20.9 ºC, Alue PU around 290.02 ± 6.85ºC, and Alue Teungku around 265±11.39 ºC. Isotope data (δD and δ18O) suggest meteoric water as the source for this manifestation. Fluid geochemical analysis indicates the potential for utilizing the geothermal manifestations of the South Zone of Mount Seulawah Agam for geothermal development or the construction of a geothermal power plant, given its high enthalpy system with an average temperature exceeding 225 ºC. Further research, including data drilling, is essential to gather precise subsurface data. Additionally, the Aceh Provincial Government should formulate policies to identify strategic areas for geothermal development, leveraging the existing exploitable potential.

Unified flash calculations with isenthalpic and isochoric constraints

In the unified flash procedure, a persistent set of unknowns and equations are solved in equilibrium calculations, allowing for simultaneous phase stability and split calculations. For fluids in a subcritical thermodynamic state characterized by pressure and temperature, modeling both liquid and gas phases with inequality conditions for phase fractions has been shown to incorporate the tangent-plane criterion and results in a consistent formulation of compositions for both present and absent phases. However, applications such as high-enthalpy systems in subsurface flow require a state definition using other state variables than pressure and temperature, as well as the capability to represent supercritical phases. Furthermore, the robustness of the flash across a wide range of state values is required if equilibrium dynamics are to be included in a flow and transport problem.This work introduces constraints in terms of enthalpy and volume to allow pressure and temperature to vary in the unified setting. The constraints are shown to arise from equilibrium conditions for the relevant state functions to be minimized. To increase the range of applicability, a modified extension procedure for the compressibility factor was devised, as well as procedures for the flash initialization.The unified formulation is extendable to allow isenthalpic and isochoric flash calculations. The initialization was devised using methodologies from the negative flash and Rachford–Rice equations. Extensive numerical tests with multiple equilibrium definitions in terms of state variables were performed. Gas–liquid, binary and a multicomponent mixture using Peng–Robinson EoS showed consistency of results which are verified using third-party code.

Geochemistry of thermal springs and associated gases along the Strymon River Valley (Bulgaria and Greece)

This paper presents and discusses the water and gas geochemistry of a large number of thermal springs occurring along the N-S trending Strymon Valley, from its source, near Sofia (Bulgaria), to the Aegean Sea (Greece). In Bulgaria springs have markedly alkaline pH, relatively low Total Dissolved Solids and prevalent Na-HCO3 to Na-Cl(SO4) in composition while the associated gas phase is mostly N2-dominated. When moving to the Greek sector, the thermal springs, Ca(Mg)-HCO3 to Na-HCO3, become less alkaline and more saline whereas the associated gas phase is CO2-dominated. The abrupt geochemical change in the Greek sector is caused by a variation in the thickness and nature of the sediments filling the Strymon Valley, the latter being characterized by a relevant amount of Neogene marine material. Such changes occur south of an important E-W lineament named Middle Mesta, south of which marble formations extensively crop out and are likely occurring below the sedimentary succession. The presence of these carbonate sequences embedded in the Neogene sediments is explaining the CO2-rich gases associated to the Greek springs. Water isotopes indicate a meteoric origin for the studied waters. From a geothermometric point of view, solute (previous studies) and gas (this work) geothermometers suggest that no high enthalpy systems occur in the Bulgaria and northern sector of Greece with estimated temperatures <120 °C. Consequently, these thermal springs can be regarded as tectonically-derived along the many fault systems that border the Strymon Valley. The convective circuits are thus originated from rainfall in the crystalline massifs that border the valley, i.e. the Serbo-Macedonian to the west and the Rhodope to the east.

A Monte Carlo based approach to the resource assessment of Jamaica's geothermal energy potential.

The Eastern Caribbean chain of islands is commonly known to exhibit high-enthalpy systems for geothermal energy exploitation. The northernmost Caribbean Community member state of Jamaica possesses physical manifestations of 12 hot springs across the island. Previous investigations indicate that of the potential 12 hot springs, Bath, Windsor and Milk River springs have cogent geothermometry of their thermal fluids with estimated temperature ranges of (80-102°C), (128-156°C), and (158-206°C), respectively. The paper provides numerical findings for each geothermal system of interest and performs Monte Carlo simulations to optimize calculated findings. The determined quantitative findings are considered under the context of environmental savings and policy regime conditions for driving geothermal energy development. The three areas of interest are situated within the Rio Minho Basin, the Dry Harbour Mountains and the Blue Mountain South Basin. Through the consideration of a 25-year lifetime for production, a collective total of 94.81 MWe of geothermal power reserves can be absorbed into the national energy mix, displacing an estimated 0.38 million barrels of oil imports, resulting in approximately 0.44 million tonnes of carbon dioxide emissions being avoided per year. This article is part of the theme issue 'Developing resilient energy systems'.

Closed-loop geothermal energy recovery from deep high enthalpy systems

Closed-loop geothermal energy recovery technology has advantages of being independent of reservoir fluid and permeability, experiencing less parasitic load from pumps, and being technologically ready and widely used for heat exchange in shallow geothermal systems. Commercial application of closed-loop geothermal technology to deep high-enthalpy systems is now feasible given advances in drilling technology. However, the technology it uses has been questioned due to differences in heat transport capacities of convective flow within the wellbores and conductive flux in the surrounding rock. Here we demonstrate that closed-loop geothermal systems can provide reasonable temperature and heat duty for over 30 years using multiple laterals when installed in a suitable geological setting. Through use of two analytical methods, our results indicate that the closed-loop geothermal system is sensitive to reservoir thermal conductivity that controls the level of outlet temperature and interference between wells over time. The residence time of the fluid in the horizontal section, calculated as a ratio of the lateral length to flow rate, dictates heat transport efficiency. A long vertical production section could cause large drops in fluid temperature in a single lateral production system, but such heat loss can be reduced significantly in a closed-loop system with multiple laterals.

Geothermal fluid circulation in a caldera setting: The Torre Alfina medium enthalpy system (Italy)

The Torre Alfina medium enthalpy geothermal field is located about 10 km north of the Bolsena caldera (Italy). The reservoir is a buried structural high consisting of fractured Meso-Cenozoic carbonate sequences and sealed by clayey flysch successions and Pliocene marine clays. We performed TOUGH2 numerical simulations, testing different model designs based on contrasting conceptual models.Results indicate that deep circulation is forced by the geometry of the reservoir and by the applied T and P gradients. We interpret the Torre Alfina field as a "blind" system, mostly recharged by lateral advection of heat and fluids from the Bolsena caldera deep high-enthalpy system, through the permeable caldera faults.

Three dimensional inversion of magnetotelluric (MT) resistivity data from Reykjanes high temperature field in SW Iceland

The resistivity structure of Reykjanes is presented, derived from a three dimensional (3D) model developed in 2016. The model is the final results of a 3D inversion of MT data, corrected for static shift by joint inversion with TEM soundings at the same location as the MT soundings. In the model presented here (REYSAND), a total of 136 sounding pairs are used for the inversion. The model covers Reykjanes area and Sandvík potential geothermal area. The resistivity structure of a high enthalpy system reflects the thermal alteration of the rock. The Reykjanes models reveal a conventional resistivity structure for a high enthalpy geothermal system, i.e. a low resistivity cap underlain by a high resistivity core. The low resistivity cap reaches surface in the hot spring area, Gunnuhver, and dips down in all directions forming an elongated area of 2.5 km × 3 km in strike direction down to 1 km depth bounded by the low resistivity. The resistivity of the low resistivity cap is less 3 Ωm and is underlain by a high resistivity core with resistivity of 10–30 Ωm down to 3 km depth. At greater depth, high resistivity anomalies are prominent with a zone of lower resistivity, in strike direction, under the main field. This zone coincides with an aseismic zone at depth and may indicate a fracture zone with higher temperature and/or permeability within the geothermal system. Comparison to data from the IDDP-2 drilling as well as seismic monitoring confirms that suggestion.

Geothermal contribution on southern Europe climate for energy efficiency of university buildings. Winter season

Geothermal energy production consists of two main types: low temperature or low enthalpy for temperatures below 150ºC, and high temperature or high enthalpy systems for temperatures over than 150ºC. In mainland Portugal the most common ground temperature varies from 20 to 40ºC, depending on the place where the geothermal boreholes are placed, which means that low enthalpy systems can be considered. Currently the increased development of ground source heat pumps (GSHP) lead to a continuous development and innovation of ground heat exchangers (GHE). The geothermal systems can contribute with savings between 25-75% of the energy demands of buildings’ HVAC systems, making it a very appealing solution mainly in northern and central Europe. The goal of this paper is to analyse the performance of a geothermal system installed in a department of the University of Aveiro, in the center of Portugal. Firstly, an introduction about different GHE systems is done and after a real case study is described and the methodology applied. To achieve the goal established, the building was analysed, audit and modeled, and an energy simulation was carried out with EnergyPlus® 8.6 (EP) software. After the results obtained it can be concluded that even in regions with mild climate as Aveiro, the geothermal system contributes with 34% of savings of the annual global primary energy needs.

Aerated Underbalance Drilling Screening Assessment at “X” Geothermal Field

&lt;p&gt;Fault network is a challenging problem for geothermal drilling operations. Formation fluid contains high temperature production fluid which can reach &amp;gt;225oC on high enthalpy system. The other consequences is that almost all fault network has low pressure or subnormal pressure. This low pressure results to a loss circulation problem. This low pressure can even go lower if the geothermal field has been exploited for a long period. A miss reservoir management, that do not re-inject sufficient amount of fluid, will cause the reservoir pressure go lower. Another problem in Indonesia is the conservation area which almost all high enthalpy geothermal system exist. The pay zone that is beneath the conservation area must be reached by directional drilling as a solution. High temperature fluid, low formation pressure and conservation areas are problems for geothermal drilling. To overcome these problems, underbalance drilling method has an advantage dealing with low pressure reservoir.&lt;/p&gt;&lt;p&gt;&lt;br /&gt;This paper introduces a way to screen the underbalance drilling method on a certain field. This study will help the quantitative and qualitative decision whether the underbalance drilling is feasible or not. The first phase qualitative decision is based on wellbore stability, loss circulation, reservoir damage, stuck pipe incident, hard drilling and cost benefit. Then it will go to the drilling fluid decision. And at the end as a quantitative decision for constructing a feasible bottom hole pressure window area with some hole cleaning assessment. Underbalance drilling assessment will be studied on field “X” at one of Indonesia’s geothermal field. The screening of “X” geothermal field comes with conclusions that it has an opportunity underbalance drilling can be implemented with vertical aerated drilling wells on spesific gas and liquid flow rates.&lt;/p&gt;&lt;p&gt; &lt;/p&gt;&lt;p&gt;&lt;strong&gt;Keywords&lt;/strong&gt;: &lt;em&gt;Geothermal, underbalance drilling, aerated drilling &lt;/em&gt;&lt;/p&gt;

The dynamic interplay between saline fluid flow and rock permeability in magmatic‐hydrothermal systems

AbstractMagmatic‐hydrothermal ore deposits document the interplay between saline fluid flow and rock permeability. Numerical simulations of multiphase flow of variably miscible, compressible H2O–NaCl fluids in concert with a dynamic permeability model can reproduce characteristics of porphyry copper and epithermal gold systems. This dynamic permeability model uses values between 10−22 and 10−13 m2, incorporating depth‐dependent permeability profiles characteristic for tectonically active crust as well as pressure‐ and temperature‐dependent relationships describing hydraulic fracturing and the transition from brittle to ductile rock behavior. In response to focused expulsion of magmatic fluids from a crystallizing upper crustal magma chamber, the hydrothermal system self‐organizes into a hydrological divide, separating an inner part dominated by ascending magmatic fluids under near‐lithostatic pressures from a surrounding outer part dominated by convection of colder meteoric fluids under near‐hydrostatic pressures. This hydrological divide also provides a mechanism to transport magmatic salt through the crust. With a volcano at the surface above the hydrothermal system, topography‐driven flow reverses the direction of the meteoric convection as compared to a flat surface, leading to discharge at distances of up to 7 km from the volcanic center. The same physical processes at similar permeability ranges, crustal depths, and flow rates are relevant for a number of active systems, including geothermal resources and excess degassing at volcanos. The simulations further suggest that the described mechanism can separate the base of free convection in high‐enthalpy geothermal systems from the magma chamber as a driving heat source by several kilometers in the vertical direction in tectonic settings with hydrous magmatism. These root zones of high‐enthalpy systems may serve as so‐called super‐critical geothermal resources. This hydrology would be in contrast to settings with anhydrous magmatism, where the base of the geothermal systems may be closer to the magma chamber.

Geologic remote sensing for geothermal exploration: A review

This paper is a comprehensive review of the potential for remote sensing in exploring for geothermal resources. Temperature gradients in the earth crust are typically 25–30°C per kilometer depth, however in active volcanic areas situated in subduction or rift zones gradients of up to 150°C per kilometer depth can be reached. In such volcanic areas, meteoric water in permeable and porous rocks is heated and hot water is trapped to form a geothermal reservoir. At the Earth's surface hot springs and fumaroles are evidence of hot geothermal water. In low enthalpy systems the heat can be used for heating/cooling and drying while in high enthalpy systems energy is generated using hot water or steam. In this paper we review the potential of remote sensing in the exploration for geothermal resources. We embark from the traditional suite of geophysical and geochemical prospecting techniques to arrive at parameters at the Earth surface that can be measured by earth observing satellites. Next, we summarize direct and indirect detection of geothermal potential using alteration mineralogy, temperature anomalies and heat fluxes, geobotanical anomalies and Earth surface deformation. A section of this paper is dedicated to published remote sensing studies illustrating the principles of mapping: surface deformation, gaseous emissions, mineral mapping, heat flux measurements, temperature mapping and geobotany. In a case study from the La Pacana caldera (Chili) geothermal field we illustrate the cross cutting relationships between various surface manifestations of geothermal reservoirs and how remotely sensed indicators can contribute to exploration. We conclude that although remote sensing of geothermal systems has not reached full maturity, there is great potential for integrating these surface measurements in a exploration framework. A number of recommendations for future research result from our analysis of geothermal systems and the present contributions of remote sensing to studying these systems. These are grouped along a number of question lines: ‘how reproducible are remote sensing products’, ‘can long term monitoring of geothermal systems be achieved’ and ‘do surface manifestations link to subsurface features’?

The Interplay of Non-static Permeability and Fluid Flow as a Possible Pre-requisite for Supercritical Geothermal Resources

Unconventional geothermal resources at supercritical conditions have been inferred to occur beneath high-enthalpy systems in active magmatic environments, and bear the potential to increase electricity production from a geothermal well by an order of magnitude. The high specific enthalpies of these fluids cannot be explained by simple convection models and a hydrologic divide between two distinct flow regimes may be required. In numerical simulations of porphyry-copper systems, such a hydrologic divide self-organized from an interplay of non-static permeability and fluid flow. The physical principles of these fossil magmatic-hydrothermal systems are closely related to supercritical geothermal systems.

Geochemistry and groundwater contamination in the La Selva geothermal system (Girona, Northeast Spain)

Hot spring waters of the La Selva geothermal system show high concentrations of Cl, F, Ca, Na, K, Li, Si, As, Ba, and Rb, whereas cold waters show low salinity, high concentrations of NO 3, and significant As content when mixed with geothermal waters. Modeling of the geothermal fluids indicates that the fluid is supersaturated with aragonite and calcite, which matches the travertine precipitation close to the present discharge areas. Moreover, the barite and fluorite are also are near equilibrium levels, indicating possible control of Ba and F solubility by these mineral phases, which also precipitate in some discharge areas. Likewise, the fluid is supersaturated with respect to quartz, indicating the possibility of siliceous precipitation near the discharge areas of the present geothermal fluids. Taking into account the Na–K, Na–K–Ca, and SiO 2-temperature geothermometers, the temperature of the reservoir may be estimated to be about 135 °C. The chemistry of the geothermal fluids has changed from a recent high-enthalpy system, which precipitated siliceous deposits, to the present low-enthalpy system, which precipitates carbonated deposits (travertine). Multivariate analysis of the groundwater shows high correlations between K, Ca, As, Br, Ag, and Ba, suggesting that As is introduced to the environment via geothermal fluids. Moreover, As concentrations in hot groundwater are associated with high concentrations of Li and Si, as has been observed in other geothermal fields. Metal concentrations in the hydrothermal deposits show high values of Ag, As, Ba, Pb, Sb, and Zn, mainly in the siliceous deposits of the town of Caldes de Malavella, where the geothermal system deposited materials with high As concentrations (123–441 ppm). The similarities between the geochemical characteristics of the hydrothermal deposits and the groundwater suggest that the metals in these deposits and fluids have the same origin.

Hydrogeochemistry of the Campania region in southern Italy

A geochemical study of thermal springs, cold springs, stream waters and natural gas emissions has been carried out in the Campania region of southern Italy. This region hosts four Quaternary volcanic areas, and thermal springs and gas emissions occur in three of them. Most thermal springs discharge Na-Cl composition waters of connate origin derived from post-orogenic volcanic and sedimentary formations. Although high-enthalpy systems are present in two of the four volcanic areas, there appear to be no magmatic contributions to the thermal springs. Solute geothermometers are unreliable as spring waters are strongly affected by mixing with “shallow” brines before discharging. Thermal springs and gas emissions also occur in non-volcanic areas, where an extensive carbonate unit acts as a regional aquifer for cold, low-salinity, bicarbonate waters. Thermal features in these areas occur in fractured zones associated with active faults. Their compositions are determined only by the type of rock encountered by solutions before surface discharge. As in other areas of north-central Italy, the widespread occurrence of hot and cold CO 2-rich springs, and gas emissions in both volcanic and non-volcanic zones, suggests a deep origin for the CO 2.

Hydrogeochemistry of the volcanic district in the Tolfa and Sabatini Mountains in central Italy

A geochemical study on 26 thermal springs and 5 samples from thermal wells ( t > 20°C), 19 cold springs, 11 cold gas pools, and 14 stream samples from the Tolfa and Sabatini Mountains volcanic district (about 1300 km 2) has clarified their genesis and evolution. Meteoric waters infiltrate the more permeable exposed rocks (carbonates and/or volcanites) and percolate down into two main aquifers. One is deep and located in Mesozoic anhydritic-carbonate formations, and is the regional geothermal reservoir that feeds springs that emerge at the margins of the carbonate series (either exposed or barely covered); its waters display typical bicarbonate-sulfate alkaline earth composition. The other aquifer(s) is shallower, consisting of waters that circulate primarily in volcanic deposits. The chemical characteristics of these shallow waters are heavily influenced by lithology and by a gas phase, mainly CO 2, originating at depth. Temperature estimates obtained with SiO 2 and gas geothermometers, which seem to be the most reliable under these conditions, indicate the widespread occurrence of deep fluids at temperatures higher than 110°C under the area covered by the Sabatini volcanites. In some areas (Manziana, Trevignano, Nepi, and Cesano) the subsurface waters reach temperatures within the range characteristic of medium to high enthalpy systems (120–160°C).

Gas geobarometry for hydrothermal systems and its application to some Italian geothermal areas

By the use of the CO 2, CH 4, H 2 and CO contents of geothermal gas discharges, the CO 2 partial pressure in the gas equilibration zone can be calculated. Assuming that the partial pressures of water at any temperature are fixed by the presence of liquid water, then the following function, which is nearly independent of temperature, linking CO 2 partial pressure to the ratio X H 2 / X C O is obtained: log ⁡ P C O 2 = 3.573 − 46 / T ( K ) − log ⁡ X H 2 / X C O Assuming a hydrostatic model, geothermal gradients for five high enthalpy and two medium to low enthalpy Italian geothermal areas have been estimated. High enthalpy systems can be clearly distinguished from those of low to medium enthalpy. Finally, accurate determinations of the H 2/CO ratio in fluids discharged by selected fumaroles in volcanic areas can provide a method of monitoring pressure conditions in geothermal aquifers. This fact is particularly useful when the risk of a phreatic explosion in a volcanic area is to be assessed.

Determination of Real-Gas Stagnation Temperature Based on Mass-Flow Consideration

ONE OF THE MAJOR PROBLEMS encountered in the operation of high-enthalpy test facilities is the determination of high stagnation temperatures (T > 4,000°R). Since these temperatures normally exceed the capabilities of available thermocouples, it is often necessary to resort to one of the various optical methods—such as pyrometry or the sodium-line reversal technique— for the determination of these temperatures. A method has been presented whereby real-gas stagnation properties in a highenthalpy system can be determined if the mass-flow rate through the system and the stagnation pressure are known. In the present analysis, this method was applied to determine stagnation temperature for stagnation pressures ranging from 100 to 1,000 atm. Nitrogen is considered to be the flow medium and the expansion of the gas from the stagnation chamber is assumed to be an isentropic and steady-state process. The maximum temperature dealt with (5,000°R) was low enough that the gas remained in an undissociated state; however, the method may be extended to other gases which may or may not be dissociated, provided the thermodynamic properties of the gas in the desired pressure and temperature range are known. A one-dimensional analysis of the flow is used to evaluate the mass flow per unit area at the throat of a nozzle for various stagnation pressures and temperatures. The evaluation of mass flow per unit area at the throat of a nozzle is a trial-and-error procedure and was performed in the following manner. Starting with an assumed stagnation pressure and temperature, an initial value of stagnation entropy was obtained from published data. , 3 The flow in the system was expanded by reducing the stagnation temperature at a constant value of stagnation entropy. At each assumed temperature the values of pressure, density, and enthalpy were obtained from Ref. 2 or 3; the velocity at each point was calculated from the energy equation. The result of the analysis is presented in Fig. 1, wherein mass flow per unit throat area is plotted against stagnation temperature. The dashed lines represent ideal-gas calculations. The spread between the ideal-gas and real-gas curves becomes larger as the stagnation pressure is increased. I t may be seen from Fig. 1 that a significant error in stagnation temperature could result by using the ideal-gas relationship. For example, a t a mass flow per unit throat area of 16,000 lb/ft-sec and a stagnation I7|-