Geothermal Applications Research Articles

Heitt Mjölnir: a heated miniature triaxial apparatus for 4D synchrotron microtomography.

Third- and fourth-generation synchrotron light sources with high fluxes and beam energies enable the use of innovative X-ray translucent experimental apparatus. These experimental devices access geologically relevant conditions whilst enabling in situ characterization using the spatial and temporal resolutions accessible at imaging beamlines. Here, Heitt Mjölnir is introduced, a heated miniature triaxial rig based on the design of Mjölnir, but covering a wider temperature range and larger sample volume at similar pressure capacities. This device is designed to investigate coupled thermal, chemical, hydraulic and mechanical processes from grain to centimetre scales using cylindrical samples of 10 mm × 20 mm (diameter × length). Heitt Mjölnir can simultaneously reach confining (hydraulic) pressures of 30 MPa and 500 MPa of axial stress with independently controlled sample pore fluid pressure < 30 MPa. This internally heated apparatus operates to temperatures up to 573 K with a minimal vertical thermal gradient in the sample of <0.3 K mm-1. This new apparatus has been deployed in operando studies at the TOMCAT (Swiss Light Source), I12 JEEP (Diamond Light Source) and PSICHÉ (Synchrotron SOLEIL) beamlines for 4D X-ray microtomography with scan intervals of a few minutes. Heitt Mjölnir is portable and modular, allowing a wide range of 4D characterizations of low-grade metamorphism and deformational processes. It enables spatially and temporally resolved fluid-rock interaction studies at conditions of crustal reservoirs and is suitable for characterization of material properties in geothermal, carbonation or subsurface gas storage applications. Technical drawings and an operation guide are included in this publication.

Review and prospect of geothermal energy application

Review and prospect of geothermal energy application

New trilobular geometry using advanced materials for experimentally validated enhanced heat transfer in shallow geothermal applications

The Adapted Conductivity Trilobular (ACT) design, comprising an up-flow central pipe and three satellite downward pipes, represents a novel configuration of a borehole heat exchanger. The novelty lies not only in the geometry of the heat exchanger, but also in the use of materials perfectly adapted to the thermal use for which they have been specified. The central pipe is constructed of a composite bilayer material with very low thermal conductivity, whereas the satellite pipes are based on a novel highly conductive plastic material. The primary objective behind this design was to simplify installation, by using essentially the same drilling and grouting methods used for conventional single-U or double-U borehole heat exchangers. In response to the rising demand for more efficient and affordable ground heat exchangers to be connected to Ground Source Heat Pump (GSHP) systems, this innovation was one of the promising outcomes of the GEOCOND European project. To assess ACT performance, the Geothermal Laboratory on the campus of the Universitat Politècnica de Valencia conducted a number of thermal response tests (TRTs), the experimental results of which are collected and analyzed in this paper. Additionally, a modified version of the Composite Two Region Line Source modeling scheme is described and used to assess the experimental data. A total of four demonstration boreholes – two single-U baseline and two ACT boreholes – have been tested. The experimental investigation using the C2RLS methodology reveals that the ACT configuration has a significantly lower thermal than the typical BHE arrangement and allows a greater specific heat injection rate. Specifically, a borehole resistance drop from 0.149 (m.K)/W to 0.07 (m.K)/W allowing higher injection rates to be achieved without an unsustainable increase in ground temperature. These findings may have significant implications for the development of more efficient and cost-effective GSHP systems.

Experimental study of nanofluid heat transfer for geothermal applications

The paper presents a performance study of a lab-scale geothermal coaxial heat exchanger with an aqueous nanofluid with the nanoparticles of Al2O3. The concentration of nanoparticles was in the interval 2% wt. to 8% wt. We describe the nanofluid production method resulting in samples that are stable in static conditions for 50 days. The average size of the particles was 183 nm in−situ. We found that the thermal conductivity of the nanofluid may increase up to 13%, and the maximum apparent viscosity grows to 20% relative to the base fluid. The nanofluid was tested in a lab-scale geothermal heat exchanger. The best thermal performance of the heat exchanger with nanofluid was 9% higher than for the experiments with the base fluid.

Design and performance of a modular 1 kilowatt-level thermoelectric generator for geothermal application at medium-low temperature

Design and performance of a modular 1 kilowatt-level thermoelectric generator for geothermal application at medium-low temperature

Infrared spectroscopy as a tool for hydrothermal alteration mineral analysis to support geothermal reservoir characterization at The Geysers, California, USA

Infrared reflectance spectroscopy (IRS), an analytical method for characterizing geologic materials, is becoming more commonly applied to geothermal energy applications. However, few case studies are available in the literature and are restricted to relatively few volcanic/geologic environments. We present an interpretation of reservoir mineralogy using IRS on drill cuttings from an active magmatic-heat-sourced geothermal system hosted in metamorphic rocks known as “The Geysers”, located in northern California and operated by Calpine Corp. Wavelength ranges investigated include the Short Wave Infrared (SWIR; 1000–2500 nm) and the Long Wave Infrared (LWIR; 2.5–20 μm). We apply this technique to a 2848 m-deep geothermal production well in the northwest Geysers, inferred to overlie a Holocene intrusion and zone of partial melt as indicated by geophysics. We utilized this non-destructive technique to analyze every drill-cuttings sample (3000+ measurements collected at ∼3.3 m intervals). We identify a zonation in mineralogy that changes from illite + chlorite ± kaolinite ± smectite ± calcite at shallow depths (0–1000 m), to illite + chlorite ± calcite at intermediate depths (1000–2200 m), to actinolite + biotite + chlorite ± tourmaline at greatest depths (2200–2848 m). We find the change at 2200 m is proximal to the inferred transition from the “normal” temperature reservoir (∼240 °C vapor-dominated convective zone) to the high temperature reservoir (up to 400 °C, conduction-dominated). We identify a possible association between 1900 nm H2O absorptions and current steam entry locations. The results of the SWIR and LWIR analysis are consistent with some caveats with newly collected bulk rock X-Ray Diffraction (XRD) data, and support and compliment previous work at the Geysers utilizing XRD and petrographic analysis.

Case study of entropy optimization with the flow of Non-Newtonian nanofluid past converging conduit with slip mechanism: An application of geothermal engineering

Magneto hydrodynamic flow over a wedge-shaped channel is often seen in geothermal applications, microelectronic, energy systems, and pumping systems. The slip condition is a normally recognized condition for the fluid flow occurs along lubricated, coated, wall channels. The best examples of such flows are the blood flow in arteries with plaque layer arteries. Flow configuration within channel is anticipated by using Carreau nanofluid injection at inlet. The intersecting wall of channel is inclined with respect to horizontal plane to make convergent angle of −α and divergent angle of α. The mathematical equations for energy and nanofluid concentration are established using well-known Navier–Stokes Equation with conservation equations invoking modified Buongiorno model. The temperature differences between the wall and core region leads to entropy. By using distinguishing amendments, system of equations are remodeled into system of ordinary differential equations (ODE's), which are numerically solved by Bvp4c technique of MATLAB for realistic conditions of under discussed phenomena. Simple shear close to the wall admit compression in local flow topology in zones of channel (divergent). The temperature field increases along thermal radiation, Brinkman number, nanoscale effects and heat source. Entropy is minimal and can be minimized with optimal angle and slip velocity.

Proof of Concept in a Full-Scale Field Test for the Novel Micro-Turbine Drilling Technology from a Cased Borehole in Granite Rock

Summary Exploration risks of geothermal projects are high, as required economic production rates are often not achieved. Stimulation methods from the oil and gas industry, such as radial jet drilling (RJD), which can be used to cost-effectively create flow paths around a main borehole, are usually not applicable in geothermal applications due to especially hard reservoir formations. Because of that, a novel technology called micro-turbine drilling (MTD®) has been developed, which allows for the drilling of micro-sidetracks from cased boreholes even into very hard reservoir rock. The approach is based on the principles of the RJD operation. However, instead of a jetting nozzle, a microdrilling turbine is used to drive a bit that mechanically drills rock. This study presents the results of the proof of concept for MTD, which was conducted in the BedrettoLab in Switzerland at a depth of up to 1,053 ft (321 m) in granite rock.

Geothermal energy system application: From basic standard performance to sustainability reflection

Shallow Geothermal Energy (SGE) systems are emerging as an attractive solution to enhance building energy efficiency and contribute to a low-carbon economy. This research investigates a SGE system comprising 40 boreholes installed in a university building located in Aveiro City under Mediterranean climate conditions. Both the building and the underground soil were monitored during the SGE operation, and EnergyPlus® software was subsequently employed for the integrated dynamic simulation. The building energy model was calibrated using field data, and a good agreement between the measured and the simulated temperatures was archived, with a Coefficient of Variance of the Root Mean Square Error (CVRMSE) below 10 %. The case study model performance was analysed and compared to other alternatives. The impact of the climate on the system performance was investigated by analyzing nine Portuguese cities situated in different climate contexts. A sustainability indicator was proposed, and an initial sustainability assessment was conducted. The results emphasize that the SGE system offered advantages compared to other alternative systems, achieving a 55 % reduction in heating and cooling energy consumption, and mitigating climate change by 405.67 ton of CO2 per 25-year lifespan. This study can guide further implementation of sustainable geothermal systems in Mediterranean climates.

Extraction turbines and feed-heating in geothermal binary plants: A thermodynamic performance assessment

The use of extraction turbines in conjunction with multiple feedwater heaters is standard practice in conventional fossil or nuclear steam electrical generating stations as a way to conserve fuel by raising the final feedwater temperature entering the boiler. One way to improve the thermal efficiency of geothermal binary plants is to include a heat recuperator that uses the expanded, but still hot working fluid leaving the turbine to preheat the working fluid leaving the feed pump prior to reaching the main brine heat exchangers. However, the use of partially-expanded working fluid from an extraction turbine to further preheat the working fluid has not been widely deployed in geothermal binary plants. This paper will describe this technique in a feed-heating cycle, develop the working equations to assess the performance for a variety of geofluid temperatures, to determine whether or not this approach can be as effective in geothermal binary plants as it is in conventional nuclear power plants. Finally, we will discuss the practical aspects of this system in geothermal binary plants, and suggest some further studies to extend this concept to other geothermal applications.

Environmental impact and thermodynamic comparative optimization of CO2-based multi-energy systems powered with geothermal energy

The continuous increase in global population and energy demands has enhanced the use of fossil fuels. The evident climate change effect in recent years has brought about the necessity to reduce fossil fuels. Hence, there exists an aggregate problem of meeting energy demands and reducing carbon emissions. Renewable energy sources have been proffered as the probable solution; however, multi-energy systems are effective options/alternatives to solving this problem. In recent literature, geothermal energy has been proposed as a renewable energy source that can continuously meet energy demands. However, there exists a significant gap in literature about the most viable temperature range for geothermal energy applications in multi-energy systems. In this study, two innovative CO2-based systems namely, high-temperature geothermal multi-energy system (HTGMES) and low-temperature geothermal multi-energy system (LTGMES) are designed, modelled, analyzed, and compared using a thermodynamic approach. While the HTGMES is modelled to predominantly use CO2 as a working fluid, a novel modified absorption system is integrated with the LTGMES. The two systems are modelled to produce electricity, cooling/refrigeration effect, space heating, hydrogen, and hot water. The energy, exergy environmental, exergy destruction, and exergoeconomic methodology is used to evaluate the performance of the innovative GMESs. Also, multi-objective optimization of the HTGMES and the LTGMES is carried out in a bid to minimize the total product unit cost and maximize overall exergy efficiency. The environmental impact analysis of the proposed system is presented considering CO2 mitigation. The results from analyses showed that the overall energetic and exergetic efficiencies in steady state are 44. 22 % and 33.5 % for the HTGMES and 45.40% and 32.9 % for the LTGMES. The optimized LCOE, LCOC, and LCOH based on the total unit cost are 0.0573 $/kWh, 0.1833 $/kWh, and 11.59 $/kg for the HTGMES; 0.0323 $/kWh, 0.0032 $/kWh, and 11.9$/kg for the LTGMES. Furthermore, the optimized exergetic performance showed that the LTGMES can achieve as high as 64.54 % and 40.96 % energy and exergy efficiency.

Integration of distributed acoustic sensing for real-time seismic monitoring of a geothermal field

To accelerate the energy transition, the exploitation of deep geothermal reservoirs is becoming a priority to supply district heating networks in areas with high potential for geothermal applications. However, the sustainable development of the resource exploitation implies minimizing the associated risks, in particular related to induced seismicity, while optimizing operational processes. Besides, the growth of this energy sector, often supported by financial aid programs, provides resources to the industry that were not available in the past to implement advanced monitoring strategies. In this context, we present a monitoring system establishing Distributed Acoustic Sensing (DAS) as an effective component of the seismic network used for the monitoring of the geothermal field of Schäftlarnstraße (Munich, Germany). We also investigate its potential for real-time seismic monitoring in an urban environment and for risk mitigation. The monitoring system is based on a data management system linking the on-site acquisition infrastructure, including the fiber optic cable deployed in an injection well and the associated DAS interrogator, to a cloud Internet-of-Things (IoT) platform. The latter is designed to deliver both a secure storage environment for the DAS recordings and optimized computing resources for their processing. The proposed solution has been tested over a six-month period under operating conditions of the geothermal field. The survey proves the feasibility of efficiently acquiring and processing the large flow of continuous DAS data. The processing outcomes, emphasized by two detected local seismic events, demonstrate the suitability of DAS, cemented behind the casing of a flowing well, for (micro-) seismic monitoring of the geothermal site. The processing applied to the data takes advantage of the high spatial density of the acquisitions for their de-noising and for the detection of events. We find that the DAS monitoring system is capable of successfully detecting an event that could not be detected by the standard surface or shallow-borehole 3C-seismometers, despite noisy conditions associated with the urban environment and the field operation. The six-month test period demonstrates the potential of DAS to be integrated as a routine seismic monitoring component of an operating geothermal field. In addition, it highlights its advantageous role as a complement to surface seismometer-based networks, particularly in urban environments.

Corrosion behaviour of HVOF developed Mo-based high entropy alloy coating and selected hard coatings for high temperature geothermal applications

The corrosion behavior of High Entropy Alloy (HEA), wear-resistant cermets, self-fluxing Ni alloy, and Fe-based amorphous alloy coatings were investigated in simulated alkaline high-temperature geothermal environments with/without H2S and CO2 gases for geothermal applications. Phase density of the corrosive fluid (liquid/vapor) influenced the corrosion behavior in the test environments. The NiCrSiBFe self-fluxing coating formed a continuous corrosion surface film while the FeCrMoWMnBCSi amorphous coating was prone to localized corrosion in the liquid phase. The cermet coatings had pores and cracks that led to localized penetration while the CoCrFeNiMo0.85 HEA showed the highest corrosion resistance in all test environments with no localized corrosion damage.

Insight into the dynamics of EMHD hybrid nanofluid (ZnO/CuO-SA) flow through a pipe for geothermal energy applications

Insight into the dynamics of EMHD hybrid nanofluid (ZnO/CuO-SA) flow through a pipe for geothermal energy applications

Application of Electromagnetic Methods for Reservoir Monitoring with Emphasis on Carbon Capture, Utilization, and Storage

The Controlled-Source ElectroMagnetic (CSEM) method provides crucial information about reservoir fluids and their spatial distribution. Carbon dioxide (CO2) storage, enhanced oil recovery (EOR), geothermal exploration, and lithium exploration are ideal applications for the CSEM method. The versatility of CSEM permits its customization to specific reservoir objectives by selecting the appropriate components of a multi-component system. To effectively tailor the CSEM approach, it is essential to determine whether the primary target reservoir is resistive or conductive. This task is relatively straightforward in CO2 monitoring, where the injected fluid is resistive. However, for scenarios involving brine-saturated (water-wet) or oil-wet (carbon capture, utilization, and storage—CCUS) reservoirs, consideration must also be given to conductive reservoir components. The optimization of data acquisition before the survey involves analyzing target parameters and the sensitivity of multi-component CSEM. This optimization process typically includes on-site noise measurements and 3D anisotropic modeling. Based on our experience, subsequent surveys tend to proceed smoothly, yielding robust measurements that align with scientific objectives. Other critical aspects to be considered are using magnetotelluric (MT) measurements to define the overall background resistivities and integrating real-time quality assurance during data acquisition with 3D modeling. This integration allows the fine tuning of acquisition parameters such as acquisition time and necessary repeats. As a result, data can be examined in real-time to assess subsurface information content while the acquisition is ongoing. Consequently, high-quality data sets are usually obtained for subsequent processing and initial interpretation with minimal user intervention. The implementation of sensitivity analysis during the inversion process plays a pivotal role in ensuring that the acquired data accurately respond to the target reservoirs’ expected depth range. To elucidate these concepts, we present an illustrative example from a CO2 storage site in North Dakota, USA, wherein the long-offset transient electromagnetic method (LOTEM), a variation of the CSEM method, and the MT method were utilized. This example showcases how surface measurements attain appropriately upscaled log-scale sensitivity. Furthermore, the sensitivity of the CSEM and MT methods was examined in other case histories, where the target reservoirs exhibited conductive properties, such as those encountered in enhanced oil recovery (EOR), geothermal, and lithium exploration applications. The same equipment specifications were utilized for CSEM and MT surveys across all case studies.

Case study: Repowering of ORC system by means of experimental test bench with supercritical carbon dioxide, proposal, and field experience improvements

Although organic Rankine cycles (ORCs) have cornered the small-scale energy harvesting market, the generation capacities produced by sCO2 cycles far exceed those of ORCs, reaching higher powers and efficiencies. This paper analyzes the results of the field tests performed in 2022 at the Grupo Dragón, Nayarit, Mexico, facilities, in which the objective was to validate the operation of the ORC IDEA-10 system with a capacity of up to 10 kWe. The thermodynamic states reached during the test time lapses in which there was full operational stability and with direct loads are analyzed. The results obtained together with proposals for improvement led to compare the performance of ORCs with sCO2 systems for low temperature geothermal sources. The efficiencies of simple sCO2 cycles (5.32%) turned out to be lower than that of ORC at the same temperatures (9.7%), however, the efficiency of the sCO2 cycle improved notably in a regenerative configuration, given the properties of CO2 near its critical point, reaching efficiencies above 25% even at low temperatures compared to conventional ORCs with efficiencies below 10%. Finally, the basis for the implementation of sCO2 in low enthalpy geothermal applications was established, designing an experimental circuit with results obtained in the literature.

Novel experimental technique to evaluate soil thermal conductivity in a transient state

novel experimental technique to evaluate soil thermal conductivity in a transient state

Neural network approach for quick dimensioning of energy walls

neural network approach for quick dimensioning of energy walls

Operational characteristics of the super-long gravity heat pipe for geothermal energy exploitation

As a novel geothermal heat transfer technology, the super-long gravity heat pipe (SLGHP) demonstrates great potential for the efficient exploitation of deep geothermal energy. Despite the rapid advances made to the SLGHP technology, its operational characteristics remain to be fully investigated. In this study, the underlying phenomenological mechanisms of the SLGHP are compared with those of normal-size gravity heat pipes (NSGHPs), and the operational characteristics of the SLGHP are analyzed in view of its distinctive geometric features. It is noted that the thermal resistance caused by the vapor flow is negligible in the NSGHPs, while it dominates the overall thermal resistance of the SLGHP. The dominance of the vapor flow thermal resistance allows making the one-dimensional simplification (along the pipe length direction) in the mathematical model of the SLGHP geothermal energy extraction system. Under these circumstances, the temperature gradient along the SLGHP length can be theoretically deduced based on the pressure drop of vapor flow. Close observation of the temperature gradient expression indicates that the desirable SLGHP working fluid should have the following properties: i) large latent heat of vaporization, and ii) a strong dependence of the saturated vapor pressure on the temperature. In cases where the saturated vapor pressure of the working fluid is highly dependent on the temperature, as in the case of ammonia, the working temperature profile of the SLGHP can be formulated as a linear function of the depth. This unique working temperature characteristic offers valuable guidance to determine the length of the SLGHP adiabatic section in practical geothermal applications. The on-site observed operational characteristics provide the necessary theoretical foundation for modeling the multiphase heat transfer process in SLGHP, which will lead to a valuable engineering analysis and design tool supporting the application and commercialization of the SLGHP technology.

Experimental research on the thermal conductivity of unsaturated rocks in geothermal engineering

The thermal conductivity of rock is an essential thermophysical parameter in geothermal engineering. Experiments have shown that when rock changes from an unsaturated to a saturated state, thermal conductivity can be increased by 50% at most. In this paper, the variation of thermal conductivity with saturation of 101 samples of six different rock types from Songliao Basin, Gonghe Basin, and Ordos Basin in China was measured in the laboratory. Correlations between saturation, porosity, internal structural characteristics of rocks and thermal conductivity were investigated. The results show that the effect of saturation on the thermal conductivity of rock increases exponentially with porosity. Based on three classical models and the relationship between porosity, saturation, and thermal conductivity, improved models and a fitted model of thermal conductivity are proposed. By comparing the improved models to the fitted model, the applicable scope of each model is obtained. The errors of each model are analyzed in detail. The average MAE value of the improved models is 0.405 and the average RMSE value is 1.207 over the applicable model scopes. The R2 of the fitted model is 0.94. Compared with experimental data from literature, MAE values of the improved models and the fitted model are 0.040 and 0.003 respectively. Unsaturated rock with a single fracture heat transfer model is established by simulation. A thermal-Hydrological coupling model is used to simulate seepage heat transfer through fracture. The effect of variable thermal conductivity simulation is the best with the experimental value, and the MAPE value was 8.3%. This study fills a gap in available models of unsaturated thermal conductivity of rock, and provide theoretical support for the accurate calculation of heat transfer efficiencies in related geothermal engineering applications.