Geothermal Field In Iceland Research Articles

Multi-Sensor Seismic Processing Approach Using Geophones and HWC DAS in the Monitoring of CO2 Storage at the Hellisheiði Geothermal Field in Iceland

Geothermal power production may result in significant CO2 emissions as part of the produced steam. CO2 capture, utilisation, subsurface storage (CCUS) and developments to exploit geothermal resources are focal points for future clean and renewable energy strategies. The Synergetic Utilisation of CO2 Storage Coupled with Geothermal Energy Deployment (SUCCEED) project aims to demonstrate the feasibility of using produced CO2 for re-injection in the geothermal field to improve geothermal performance, while also storing the CO2 as an action for climate change mitigation. Our study has the aim to develop innovative reservoir-monitoring technologies via active-source seismic data acquisition using a novel electric seismic vibrator source and permanently installed helically wound cable (HWC) fibre-optic distributed acoustic sensing (DAS) system. Implemented together with auxiliary multi-component (3C and 2C) geophone receiver arrays, this approach gave us the opportunity to compare and cross-validate the results using wavefields from different acquisition systems. We present the results of the baseline survey of a time-lapse monitoring project at the Hellisheiði geothermal field in Iceland. We perform tomographic inversion and multichannel seismic processing to investigate both the shallower and the deeper basaltic rocks targets. The wavefield analysis is supported by seismic modelling. The HWC DAS and the geophone-stacked sections show good consistency, highlighting the same reflection zones. The comparison of the new DAS technology with the well-known standard geophone acquisition proves the effectiveness and reliability of using broadside sensitivity HWC DAS in surface monitoring applications.

Carbon capture and utilization: More than hiding CO2 for some time

Carbon capture and utilization: More than hiding CO2 for some time

Prospects for Power Generation of the Doublet Supercritical Geothermal System in Reykjanes Geothermal Field, Iceland

Supercritical geothermal resources are in the preliminary exploration stage as a new type of clean energy and there are no practical utilization projects. The IDDP-2 well at Reykjanes geothermal field in Iceland encountered supercritical geothermal conditions in 2017, with a maximum temperature of 535 °C. The system is still in the field experiment stage and no exploitation work has been carried out. Hence, a hypothetical doublet geothermal system was simulated based on IDDP-2 to study the power generation potential and favorable operating conditions for future development of supercritical geothermal resources. A multiphase flow model is established to predict the fluid and heat flow characteristics. Furthermore, sensitivity and economic analyses were performed to evaluate the expected commercial and environmental benefits of the supercritical geothermal system. The results show that the system’s evolution could be briefly divided into three stages according to the temperature variation. The power generation ranges between 5.4 MW~16.5 MW, and the levelized cost of electricity (LCOE) is 0.02 $/kWh. In addition, the system can reduce CO2 emissions, which are 1.2~7.75 Mt less than that of fossil fuel plants with the same installed capacity. The results prove the great development potential and commercial competitiveness of the supercritical geothermal system.

Monitoring microseismicity of the Hengill Geothermal Field in Iceland

Induced seismicity is one of the main factors that reduces societal acceptance of deep geothermal energy exploitation activities, and felt earthquakes are the main reason for closure of geothermal projects. Implementing innovative tools for real-time monitoring and forecasting of induced seismicity was one of the aims of the recently completed COSEISMIQ project. Within this project, a temporary seismic network was deployed in the Hengill geothermal region in Iceland, the location of the nation’s two largest geothermal power plants. In this paper, we release raw continuous seismic waveforms and seismicity catalogues collected and prepared during this project. This dataset is particularly valuable since a very dense network was deployed in a seismically active region where thousand of earthquakes occur every year. For this reason, the collected dataset can be used across a broad range of research topics in seismology ranging from the development and testing of new data analysis methods to induced seismicity and seismotectonics studies.

Induced seismicity associated with geothermal fluids re-injection: Poroelastic stressing, thermoelastic stressing, or transient cooling-induced permeability enhancement?

Both field injectivity and induced seismicity were reported to be inversely correlated with the temperature of re-injected fluids at the Hellisheiði geothermal field in Iceland. This observation has led to a hypothesis that transient cooling-induced permeability enhancement is a novel mechanism for induced seismicity, in addition to elevated fluid pressure, poroelastic stressing, and thermoelastic stressing in geothermal environments. In this work, a 3D calibrated coupled THM model was developed to model the colder fluids re-injection process over a 1-year period and evaluate the potential for induced seismicity in terms of Coulomb stress changes at the Hellisheiði geothermal field. Three modelling scenarios taking into account respectively the poroelastic effect, thermoporoelastic effect, and thermoporoelastic effect with permeability enhancement, were examined and compared to identify the dominant mechanism for the recorded seismicity and examine the contribution from each individual mechanism. Results have shown that, under normal fluid re-injection pressure and temperature conditions, the permeability enhancement effect is the dominant mechanism for induced seismicity at the Hellisheiði geothermal field. Specifically, the contribution to Coulomb stress changes from the permeability enhancement effect is almost twice of that from the thermoelastic stressing, which is in turn two orders of magnitude larger than that from the poroelastic stressing. It has also been noted that, when reducing temperature of re-injected fluids from 120°C to 20°C, the temperature change is increased by 2.1 times at 1,000 m depth, while the amount of mass flow by around 4 times. Thus, the amount of heat transferred can be increased 8.4 times by lowering temperature of the injected fluids, which explains the high sensitivity of induced seismicity to temperature. Outcomes of this work suggest temperature control of injected fluids as a feasible regulation method to mitigate against injection-induced seismic risk in geothermal reservoirs.

Hydrogen emissions from hydrothermal fields in Iceland and comparison with the Mid-Atlantic Ridge

Hydrogen emissions from geothermal systems are well known, for example associated with mafic and ultramafic rock formations along mid-ocean ridges (MOR). Here we report concentrations and emissions for H 2 from geothermal fields in Iceland that provides the only MOR on Earth that exposes a largely submarine rift on land and compare them with submarine vent systems along the mid-Atlantic Ridge (MAR). The concentrations of H 2 in Icelandic hydrothermal fluids are 0.022–20.5 mmol/kg comparable to H 2 concentrations in MAR hydrothermal fluids of 0.07–26.5 mmol/kg. According to geochemical modeling, the H 2 is considered to form in these settings associated with chemical reactions of primary mineral leaching, Fe +II to Fe +III oxidation and secondary mineral precipitation and reduction of water to hydrogen. The main factors influencing these reactions are rock type and source water composition. Geothermal power plants in Iceland emit in total ∼1.2 kt H 2 per year (2019–20) or on average ∼0.7 g/MWh. The H 2 is today emitted to the atmosphere but could in principle be utilized given technical aspects of such extraction are implemented. • Large quantities of H 2 are present in the fumaroles and the steam of the power plants of Iceland. • The higher values are found along the active volcanic zone. • The salinity and the type of water influence the H 2 generation from the mafic and ultra-mafic rocks. • If we consider a price of H 2 of 2€/kg, the native H 2 emitted by the existing power plants corresponds to 2.3 million €/yr.

Seismic velocity characterisation and survey design to assess CO2 injection performance at Kızıldere geothermal field

The noncondensable gases in most geothermal resources include CO2 and smaller amounts of other gases. Currently, the worldwide geothermal power is a small sector within the energy industry, and CO2 emissions related to the utilisation of geothermal resources are consequently small. In some countries, however, such as Turkey and Iceland, geothermal energy production contributes significantly to their energy budget, and their CO2 emissions are relatively significant. SUCCEED is a targeted innovation and research project, which aims to investigate the reinjection of CO2 produced at geothermal power production sites and develop, test, and demonstrate at field scale innovative measurement, monitoring and verification (MMV) technologies that can be used in most CO2 geological storage projects. The project is carried out at two operating geothermal energy production sites, the Kızıldere geothermal field in Turkey and the CarbFix project site at the Hellishei?i geothermal field in Iceland. Together with a brief description of the project, this paper presents the details of the two field sites and the progress made in seismic velocity characterisation and modelling relevant to the Kızıldere geothermal field in Turkey.

High temperature generation and equilibration of methane in terrestrial geothermal systems: Evidence from clumped isotopologues

Fluids emanating from geothermal areas contain trace quantities of methane and other simple hydrocarbons. These hydrocarbons are thought to derive from thermal cracking of organic matter dissolved in circulating meteoric or seawater or found in pre-existing organic-rich sedimentary rocks, but an abiotic origin has also been proposed. We measured the relative abundances of four CH4 isotopologues (12CH4, 13CH4, 12CH3D, and 13CH3D) in hydrothermal gases discharged by steam vents and geothermal wells from Iceland and Nisyros island (Greece) in order to investigate the origin of methane. Measured methane samples yielded consistently low Δ13CH3D values (13CH3D abundance relative to stochastic) of 0.82–1.77‰, which correspond to high apparent temperatures of isotopologue equilibrium (TΔ13CH3D = 278–490 °C). Hydrothermal well fluids from the Krafla and Námafjall geothermal fields in Iceland yielded the lowest Δ13CH3D values, and thus the highest Δ13CH3D-based temperatures averaging 438-45+55 °C. Those samples also show the most pronounced departures in δDCH4 and δ13CCH4 values expected for isotopic equilibrium with respect to δDH2O and δ13CCO2. In contrast, CH4 samples from natural steam vents in other Iceland locations and in Nisyros have slightly higher Δ13CH3D values (with TΔ13CH3D=351-35+42 °C) and have δDCH4 and δ13CCH4 values that are consistent with those expected for isotopic equilibrium with both H2O and CO2. The short fluid residence times (1–50 years) in systems that are exploited for geothermal energy, such as Krafla and Námafjall, combined with the proximity of a hot magma chamber, favor the preservation of kinetic signals. The initial disequilibrium δDCH4 and δ13CCH4 values are consistent with a thermogenic origin from immature organics dissolved in hydrothermally heated groundwater, but an abiotic origin cannot be excluded. The high apparent Δ13CH3D-based temperatures at Krafla and Námafjall could therefore represent nonequilibrium signals associated with either pyrolysis or abiotic generation of CH4 in a superheated vapor or supercritical water phase (>374 °C), considered to exist in the roots of the system above the magmatic heat source. Isotopologue equilibration calculations demonstrate that under such conditions (e.g. > 400 °C) kinetic signals would be erased in days to months, implying rapid migration and quenching of CH4 into the overlying subcritical (<300 °C) hydrothermal reservoir fluids. In systems with longer fluid residence times such as Nisyros, equilibrium isotopologue distributions at temperatures of ~ 350 °C are consistent with long fluid residence times on the order of > 100 years. Our calculations further reveal that CO2–CH4 isotopic equilibration requires unreasonably long fluid residence times, suggesting that any apparent 13C equilibrium may be coincidental.

SUCCEED: A CO2 storage and utilisation project aimed at mitigating against greenhouse gas emissions from geothermal power production

The non-condensable gases in most geothermal resources include CO2 and smaller amounts of other gases. Currently, the worldwide geothermal power is a small sector within the energy industry, and CO2 emissions related to the utilisation of geothermal resources are consequently small. In some countries, however, geothermal energy production contributes significantly to their energy budget and their CO2 emissions are relatively significant. SUCCEED is a targeted innovation and research project which aims to investigate the reinjection of CO2 produced at geothermal power production sites and develop, test and demonstrate at field scale innovative measurement, monitoring and verification (MMV) technologies that can be used in most CO2 geological storage projects. The project is carried out at two operating geothermal energy production sites, the Kizildere geothermal field in Turkey and the CarbFix project site at the Hellisheiði geothermal field. Together with a brief description of the seismic monitoring technologies proposed in the project, this paper presents the details of the two field sites and the progress made in installing and testing of the surface fibre-optic cables at the Hellisheiði geothermal field in Iceland.

Silicon isotope variations in hydrothermal systems at Yellowstone National Park, Wyoming, U.S.A.

Silicon (Si) isotopic compositions of authigenic Si-bearing materials can be powerful tracers of geological Si cycling and reconstruction of Earth’s climate. Interpretations of Si isotope data, however, are complicated by an inadequate understanding of natural Si isotopic fractionation pathways. This study investigated Si isotope fractionation between hydrothermal fluids and amorphous silica sinters of Cistern Spring and Deerbone Spring at Yellowstone National Park, USA, with a particular focus on spatial variations along spring flowpaths. Modeling of geochemical data indicate that the fluids at Cistern Spring were supersaturated with respect to amorphous silica whereas the fluids at Deerbone Spring were undersaturated due to lower SiO2 content and a more alkaline pH. The δ30Si values of the spring waters for both sites exhibit small variations, whereas the associated amorphous silica sinters displayed a considerable range and generally decreased downflow (from − 2.25 to −5.04‰ for Cistern and from −0.11 to −0.81‰ for Deerbone). The magnitude of apparent isotopic fractionation between solid and aqueous silica (Δ30Sisolid-fluid) was significantly larger for the samples from Cistern Spring than for Deerbone Spring or similar hot spring systems at Geysir geothermal field in Iceland. The Δ30Sisolid-fluid values for Cistern Spring ranged from −2.40 to −5.49‰ along the flowpath and correlated inversely with the rate of silica precipitation, indicating a process dominated by kinetic isotope fractionation. In contrast, the magnitude of Si isotopic fractionation was significantly smaller at Deerbone Spring (+0.21 to −0.64‰). A portion of the opaline sinters at Deerbone may have formed cryogenically under freezing winter conditions that altered silica saturation and formation pathway. Rapid isotope exchange with silica undersaturated hydrothermal fluids may have erased initial kinetic isotope effects. Re-equilibration between opal-A and fluids was strongly affected by isotopic fractionation between aqueous silica species and fluid ionic strengths. These results document both kinetic and equilibrium Si isotope fractionation from field observations and highlight the pivotal role of fluid-rock interaction on the preservation of Si isotope signatures in the rock record.

Casing-to-casing resistance study performed at Reykjanes geothermal field in Iceland to estimate fracture connectivity

Successful drilling of geothermal wells into fractured hot rock through which geothermal fluid flows is critical to ensure efficient operation of geothermal power plants. This study focuses on investigating a casing-to-casing resistance method for estimating fracture connectivity between wells at Reykjanes geothermal reservoir in Iceland to better understand the fluid-flow in the reservoir. Conductive well casings were successfully used as electrodes to transfer the electric current deeper into the fractured reservoir in an electrical resistance survey. The low resistance measured between wells implies that the wells are connected to the main production zone at Reykjanes and that the current is travelling through fractures filled with conductive geothermal brine from one well casing to another rather than going through a less conductive rock. The measured resistance is compared to an analytical study showing the promising potential the casing-to-casing resistance method has for gaining valuable information about the fracture connectivity in geothermal reservoirs.

Materials investigation of the high temperature IDDP-1 wellhead

The Iceland Deep Drilling Project (IDDP) well IDDP-1 in the Krafla geothermal field in Iceland is the most powerful geothermal well on record, with a maximum wellhead temperature of 452 °C and 140 bar pressures. In the end, the well had to be abandoned and closed permanently due to several casing failures, including a number of collapses and tensile coupling failures of the innermost casing – the production casing. The history of this first IDDP well is discussed in this paper, revealing the conditions the carbon steel was exposed to. The metal samples degrading mechanism was investigated by mechanical testing and microstructure analysis. For the first time, material used in geothermal steam in situ above 400 °C for a long period was investigated and a new alarming cracking mechanism detected. This cracking mechanism due to formation of methane inside the carbon steel structure results in severe cracks and as a result the steel loses its strength and ductility. This study reveals the need for review of material selection for high-temperature geothermal wells.

Monitoring geothermal reservoir developments with the Controlled-Source Electro-Magnetic method — A calibration study on the Reykjanes geothermal field

Surface geophysical monitoring techniques are important tools for geothermal reservoir management as they provide unique information on the reservoir development away from boreholes. For magmatic environments, electromagnetic (EM) methods are attractive monitoring tools as they allow to characterize the reservoir and hence potentially monitor changes related to fluid injection/production. Indeed, the electrical resistivity of reservoir rocks is highly dependent on the volume, chemistry and phase of the in-situ geothermal brine (e.g. liquid, vapor, supercritical).Passive EM techniques (e.g. magnetotellurics or MT) are traditionally used for geothermal exploration and a few recent studies have demonstrated its potential for monitoring reservoir development. One of the main challenges is though the presence of cultural noise and/or variability of the Earth magnetic field that can obfuscate the EM signals of interest. We have investigated the benefits and drawbacks of active EM surveying (Controlled-Source EM or CSEM) to tackle this challenge, first with a synthetic study and subsequently with an actual time-lapse survey acquired in 2016 and 2017 over the Reykjanes geothermal field in Iceland before (baseline) and after (monitor) the thermal stimulation of the supercritical RN-15/IDDP-2 geothermal well.The synthetic study showed that for geothermal fields having a resistivity structure similar to the Reykjanes field (i.e. a conductive caprock overlying a more resistive higher temperature reservoir), CSEM and MT measurements can both detect resistivity changes within the deep resistive reservoir, provided that measurement errors are small. Variations in many survey parameters (e.g. errors in receiver position/orientation, differences in recording devices, variations of near surface conditions, external noise) can create significant time-lapse CSEM measurement errors. Our actual time-lapse survey showed that when similar CSEM equipment is used during the baseline and monitor surveys and systematically d-GPS positioned, the remaining key parameter controlling the survey repeatability is the level of external noise. Since the influence of external noise on CSEM data can be artificially reduced (e.g. by increasing the transmitter dipolar moment), it offers the possibility to adapt the survey design to increase the chance of detecting the time-lapse signals of interest. On the contrary, little control is possible on the MT signal to noise ratio and hence repeatability.The time-lapse EM survey acquired over the Reykjanes geothermal reservoir showed indeed that a high CSEM survey repeatability can be achieved with electric field measurements (within a few percent) but that time-lapse MT survey is a challenging task because of the high level of cultural noise in this industrialized environment. To assess the quality of our CSEM dataset, we inverted the data and confronted the resulting resistivity model with the resistivity logged in the RN-15/IDDP-2 well. We obtained a good match up to 2-3km depth, i.e. enough to image the caprock and the liquid-dominated reservoir but not deep enough to image the reservoir in supercritical conditions. To obtain such an image, we had to jointly invert legacy MT data with our CSEM data. On the monitoring aspects, the analysis of changes in electric fields did not allow to identify any CSEM signal related to the thermal stimulation of the RN-15/IDDP-2 well. One possible explanation is the weakness of the time-lapse CSEM signal compared the achieved CSEM survey repeatability as a result of a limited resistivity change over a limited volume within the reservoir. Future reservoir developments in the supercritical reservoir (e.g. hydraulic stimulation, long-term fluid circulation) will most likely generate stronger resistivity variations over a larger volume than during the thermal stimulation of the well. This calibration study provides the basic information for deciding when and how an EM monitor survey must be performed for the monitoring of the Reykjanes geothermal reservoir but also for the definition of the monitoring strategy of similar high-enthalpy geothermal reservoirs.

Underwater and drone based photogrammetry reveals structural control at Geysir geothermal field in Iceland

Geysers are local hydrothermal vents with periodic gas bubble driven explosions at the surface. Little is known, however, on the control on distribution, the dynamics and the geometry of the conduits of geysers. To better understand the link between the deep and surface expression at the Geysir geothermal field, Iceland, a detailed analysis of the spatial distribution of the thermal expressions, and their relationship to the tectonic framework was carried out. By use of high resolution unmanned aerial vehicle (UAV) based optical and radiometric infrared cameras, we are able to identify 364 distinct thermal spots distributed over the area. Close analysis of their arrangement yields a clustered appearance, following a preferred direction that is found to be consistent with the assumed tectonic trend in the area. Furthermore by using underwater cameras we are able to obtain for the first time detailed images from the two largest geysers at depths exceeding 20m. Near to the surface, the conduit of the geysers are near circular, but at a depth of 9–12m the shape changes into a crack-like elongated fissure. The elongation direction of these deep cracks is consistent with the identified thermal expression at the surface, highlighting a structural or even tectonic control at the Geysir geothermal field, which may also explain the susceptibility for seismically triggered activity changes.

Redescription of Dexiotricha colpidiopsis (Kahl, 1926) Jankowski, 1964 (Ciliophora, Oligohymenophorea) from a Hot Spring in Iceland with Identification Key for Dexiotricha species.

We isolated an encysted ciliate from a geothermal field in Iceland. The morphological features of this isolate fit the descriptions of Dexiotricha colpidiopsis Kahl, 1926) Jankowski, 1964 very well. These comprise body shape and size in vivo, the number of somatic kineties, and the positions of macronucleus and contractile vacuole. Using state-of-the-art taxonomic methods, the species is redescribed, including phylogenetic analyses of the small subunit ribosomal RNA (SSU rRNA) gene as molecular marker. In the phylogenetic analyses, D. colpidiopsis clusters with the three available SSU rRNA gene sequences of congeners, suggesting a monophyly of the genus Dexiotricha. Its closest relative in phylogenetic analyses is D. elliptica, which also shows a high morphological similarity. This is the first record of a Dexiotricha species from a hot spring, indicating a wide temperature tolerance of this species at least in the encysted state. The new findings on D. colpidiopsis are included in a briefly revision of the scuticociliate genus Dexiotricha and an identification key to the species.

Machine learning for creation of generalized lumped parameter tank models of low temperature geothermal reservoir systems

Lumped parameter tank models have gained renewed interest in recent years as an alternative tool for geothermal reservoir analysis and production planning. The models can be structured in various ways regarding the number of tanks, connections between the tanks and the parameters representing the physical properties of the geothermal system. It usually requires a time consuming and difficult process of trials and errors to manually decide the optimal configuration of a tank model. Inspired by recent development in the use of machine learning methods, we propose a method for automatically generating accurate and computationally feasible generalized tank models for isothermal, single phase, reservoirs. This is an extension of earlier work on complexity reduction of generalized tank models (Li et al., 2016). Here, a recursive “switch-back” method is constructed to maximize prediction accuracy of the model. It is also shown how the K-means clustering algorithm can be used to aggregate production wells in generalized tank models. One synthetic example and one field application from t Reykir geothermal fields in Iceland are used to illustrate the effectiveness of these methods.

Structural modeling of the casings in the IDDP-1 well: Load history analysis

Flow testing of IDDP-1, the first Icelandic Deep Drilling Project (IDDP) well drilled in the Krafla geothermal field in Iceland, demonstrated promising results by producing superheated steam. During an unavoidable quenching of the well the innermost casing failed presumably due to tensile stresses caused by thermal contraction. Since the structural integrity of casings is essential for utilization of high temperature geothermal wells, the well has not been discharged again. In this paper, the casings of the well are analyzed structurally with a nonlinear finite-element model. The load history of the casings is followed from installation and through several thermal cycles, but the well was discharged at least six times before it was quenched with cold water. The results show that changes in stiffness due to the presence of casing shoes and changes in casing thickness have an effect on the stress and strain formations in neighboring casings. The results illustrate that during each thermal cycle, the wellbore thermal load is more severe for the production casing than for the external casings that are somewhat protected, provided that cementing in between is adequate.

Pilot testing of handling the fluids from the IDDP-1 exploratory geothermal well, Krafla, N.E. Iceland

Material tests and scrubbing experiments were carried out at the IDDP-1 well in the Krafla geothermal field in Iceland. The 450°C superheated steam contained acid gas (approx. 90mg/kg HCl and 7mg/kg HF) and was highly corrosive when it condensed making it unsuitable for utilization without scrubbing. The acid gas could effectively be scrubbed from the steam with water. The steam contained gasous sulfur compond (80–100mg/kgS), which could only be scrubbed from the steam with alkaline water. The steam contained both silica dust and dissolved silica which was effectively washed from the steam with wet scrubbing. Experiments on corrosion and erosion resistance of metals and alloys were problematic to run because of equipment clogging by silica dust.

The concept of the Iceland deep drilling project

Calculations discussed in the Iceland Deep Drilling Project feasibility study in 2003 indicated that, for same volumetric flow rate of steam, a geothermal well producing from natural supercritical fluid would have the potential to generate power outputs an order of magnitude greater than from conventional high-temperature wells (240–340°C). To reach supercritical hydrous fluid conditions in natural geothermal systems requires deep drilling to a minimum depth of some 3.5–5km were temperature conditions can be expected to range between 400 and 600°C in reasonably active high-temperature fields. Three geothermal fields in Iceland, Reykjanes, Hengill and Krafla, were selected as suitable locations for deep drilling to test this concept in search of natural supercritical geothermal fluid systems.

Lumped-parameter models for low-temperature geothermal fields and their application

The behavior of low-temperature geothermal reservoirs under exploitation is simulated using analytical lumped-parameter models. These models consider the effects of fluid production and reinjection, as well as natural recharge, on the pressures (or water levels) of low-temperature, liquid-dominated geothermal systems. The computed responses for constant production/injection flow rates are given in the form of analytical expressions. Variable flow rate cases are modeled, based on the Duhamel's principle. Reservoir parameters are obtained by applying a weighted nonlinear least-squares estimation technique in which measured field data are history matched to the corresponding model response. By using history-matched models, the future performance of the reservoir can be predicted for different production/injection scenarios in order to optimize the management of a given geothermal system. We demonstrate the applicability of the models by simulating measured data from the Laugarnes geothermal field in Iceland, and the Balcova–Narlidere field in Turkey.