Geothermics最新文献

Cement pastes of different compositions were hydrated in a geothermal solution with the simultaneous action of high temperature (150 °C) and pressure (18 MPa) for 7 days. The influence of solution on phase composition and compressive strength of pastes was investigated based on the comparison with hydration in water and using TGA, XRD, FTIR, ²⁹Si, and ²⁷Al NMR. The geothermal solution accelerated hydration and pozzolanic reactions. A higher amount of more thermally stable products was formed. Undesired transformation to crystalline α-C₂SH in the samples with the highest C/S ratio was restricted. The uptake of carbonates from the solution led to an increased amount of calcite. As a result, increased compressive strength values were determined. Preferential incorporation of Al³⁺ into the structure of C-(A-)S-H or hydrogrossular phases depended on the composition of cement pastes.

Limiting global temperature rise to between 1.5 and 2 °C will likely require widespread deployment of carbon dioxide removal (CDR) to offset sectors with hard-to-abate emissions. As financial resources for decarbonization are finite, strategic deployment of CDR technologies is essential for maximizing atmospheric CO₂ reductions. Carbon capture and sequestration (CCS), using either direct air capture (DACCS) or bioenergy (BECCS) technologies has a particular synergy with geothermal electricity generation. This is because expensive geothermal infrastructure can be leveraged to transport dissolved CO₂ for storage in subsurface reservoirs.

Here, we present a techno-economic comparison of renewable electricity generation coupled with either BECCS or DACCS at high-temperature, low-gas hydrothermal systems. We use a systems model that quantifies energy, carbon and financial flows through a generic hybrid power plant. At a CO₂ market price of $100/tonne, the geothermal-BECCS system has a lower median cost of electricity generation ($88/MWh) than geothermal-DACCS ($181/MWh) and conventional geothermal ($89/MWh).

Geothermal-BECCS also had the lowest costs of overall emissions abatement, $122/tCO₂, accounting for carbon removal and assuming displacement of fossil-fuel generation. Abatement costs are even lower, $45/tCO₂, for BECCS retrofit of existing geothermal plants, owing to discounted costs of pre-existing injection wells, steam fields, and plant equipment.

For a case study based on a geothermal field in New Zealand's Taupō Volcanic Zone (TVZ), we determined that achieving CDR rates of 1 MtCO₂/year via new geothermal-BECCS builds would require 62 standard geothermal wells and 790 kt/year of feedstock and result in 511 MWe in installed capacity. In contrast, geothermal-DACCS would need 49 wells and no external fuel source to achieve 1 MtCO₂/year scale but result in only 190 MWe in installed capacity. Both pathways are calculated to require similar upfront investment costs at $2.2 billion and $2.3 billion for geothermal-BECCS and geothermal-DACCS respectively.

Although geothermal-DACCS removes CO₂ at high rates, its high parasitic load increases the overall decarbonization cost ($187/tCO₂). In contrast, when biomass hybridization is considered, geothermal-BECCS has a lower cost of emissions abatement and produces 20 % more electricity than the benchmark geothermal plant. We conclude that this increase in electricity production makes geothermal-BECCS the more cost-effective geothermal-based CDR configuration. Finally, we argue that revenues from net-negative CO₂ emissions and increased power production make geothermal-CDR a cost-competitive decarbonization technology.

For the air-water source coupling heat pump (A-WSCHP) system, the water supply temperature of the intermediate loop (T_WS-INT) directly affects the performance of the two heat pump units, which makes the system characteristics change. In this study, an A-WSCHP system located in Taiyuan, China, was experimentally studied. According to the experimental results, the effects of different intermediate loop water supply temperatures on system coefficient of performance (COP), energy consumption, and equipment characteristics under low-temperature heating conditions were analyzed. The results show that the performance of the A-WSCHP system is strongly consistent with that of the air source heat pump (ASHP) unit, as the T_WS-INT changes in the range of 25.0 ∼35.0 ℃. With the decrease of the T_WS-INT, the power consumption of the system is greatly reduced, the COP is obviously improved, and the number of starts and stops of the ASHP unit is reduced, which is more beneficial to extending the service life of equipment and improving the stability of the system.

Aquifer thermal energy storage (ATES) is attained by storing thermal energy in aquifers, using the groundwater as a carrier for the heat. Hence, in ATES systems, the background groundwater flow velocity may affect the efficiency if a significant amount of stored heat is moved away from the storage well by advection. This paper presents an alternative solution to the typical “pump and dump” open-loop shallow geothermal system configuration using the ATES concept with a reversed extraction-injection well scheme. This particular placement is able to increase the energy efficiency of a conventional open-loop system while reducing the thermal impact downstream the system.

The uni-directional ATES pumping scheme compensates the heat transport by groundwater flow extracting the groundwater from the downstream well and re-injecting back in the upstream well. This research presents a numerical feasibility study and sensitivity analysis of the effects of the well spacing, pumping scheme and groundwater flow velocity on the efficiency of a uni-directional ATES. Optimal combinations are suggested to ensure the maximum re-capture by the downstream well of the heat injected in the upstream well in the previous season and subject to thermal transport by advection, with a maximum heat recovery between 55 and 75 % depending on the conditions. The results of the modelling analysis showed that the optimal inter-well distance depends on the groundwater flow velocity and the total annual storage volume. This paper also demonstrates the mitigation effect of the thermal perturbation downstream of a uni-directional ATES compared to a conventional open-loop scheme.

The understanding of heat transport in fractures is crucial for mining geothermal systems. Studies of heat transport in natural fractures at scales comprised between those of laboratory experiments and those of field tracer tests are seldom. To bridge the gap, a joint surface with characteristic plumose was scanned in the field using LiDAR technology. The scanned surface was used to build a numerical model of mode 1 fracture. Fluid flow and heat transport were modeled solving the steady-state Stokes equation and assuming Fourier transport, respectively. We considered three different fracture apertures and varied systematically roughness in order to investigate the impact of plumose on fluid and heat transport. The 3D velocity flow fields were characterized by mean hydraulic aperture and by statistics on the directional components of the velocity vector. The method of temporal moments was used to extract first and second moments from temperature breakthrough curves. Heat transport parameters (local and macroscopic) were calculated from first and second moments.

We show that hydraulic aperture and the longitudinal component of the velocity vector decrease with increasing roughness. The local variation of heat transport parameters is controlled by fracture roughness. For the macroscopic transport parameters, several transport regimes were identified. At low fracture aperture (i.e. 1 mm), conductive regime dominates heat transport in agreement with low Péclet numbers. In this case, fracture roughness affects the transport parameters via the loss of hydraulic aperture. With higher aperture (i.e. 3 mm) geometrical dispersion regime is dominant, roughness controlling the amplitude of transport parameters. At 5 mm aperture, transition from geometrical to Taylor dispersion occurs and the roughness tends to decrease dispersion and dispersivity according to the mean flow velocity.

Shallow geothermal energy is increasingly adopted for heating and cooling purposes because of the short pay-back time of initial installation investments. As a result, a relevant concentration of Ground Heat Exchangers is being experienced in urban areas. Planning issues thus arise to manage interferences and optimize the use of underground heat resources without depletion, harm to the environment nor efficiency losses on heat pumps or plant oversizing. This study provides a rational approach to optimise geothermal resources based on the use of Geographic Information Systems and transient 3D Thermo-Hydro numerical models. An optimised semi-analytical formula for the assessment of Borehole Heat Exchangers geothermal potential in hydrodynamic conditions is developed through a parametric numerical study. The long-term performances of BHE subjected to groundwater velocity in the range of 0 to 1 m/day were analysed with multiple aquifer thermal parameters. This analytical expression allows a fast and accurate assessment of the potential even in large areas without leading to excessively conservative evaluations. This may serve designers in the preliminary sizing of installations and city planners in the development of appropriate policies for the promotion and management of shallow geothermal resources. An example of the application to the central district of the city of Turin (Italy) is also shown.

Evaluating the thermo-mechanical response of rocks under high temperature treatments is crucial for various engineering geology projects. Current predictions of rock thermo-mechanical response rely on simplistic mathematical fittings treating temperature as a reduction factor, while existing machine learning algorithms often present practical challenges due to their black-box solutions. In this study, highly practical grey-box solutions, utilizing gene expression programming (GEP) are proposed for forecasting rock strength following high-temperature treatments. The dataset, comprising temperature, rock type, rock density, sample size, crack damage stress, confining pressure, and elastic modulus, serves as input parameters, with rock strength from triaxial compression tests as the output. Three grey-box solutions (mathematical formulations) based on distinct input parameter sets are proposed, all demonstrating excellent accuracy with high R²-values (R² > 0.95) and low error values across both the training and testing phases. Feature importance analysis highlights crack damage stress, confining pressure, and elastic modulus as statistically significant parameters influencing the strength of rocks subjected to high temperatures. External validation of the proposed models indicates strong generalization capabilities, underscoring their ability to perform well beyond the training data. Furthermore, a monotonicity study demonstrates that the proposed models align with the expected physical processes. The proposed formulations offer valuable field implications, effectively addressing the limitations of labor-intensive and costly laboratory processes for evaluating rock thermo-mechanical responses.

This paper builds on four earlier papers detailing the results of the Hawai‘i Play Fairway (PF) project's first two phases. In Phase 3 the project deepened a water well on the rim of the caldera of Lāna‘i Volcano to a maximum depth of just over 1 km. Due to funding constraints, the project deepened an already existing water well that was proximal to our area of highest resource probability within the caldera. Drilling preparation included: completion of an Environmental Assessment, lowering a camera down the well, deviation logging, coordinating site preparation, procure and shipping, and participating in multiple community meetings. Drilling occurred 24/7 the entire month of June 2019. The project deepened Lāna‘i Well 10 from 427 m to 1057 m, while collecting continuous core, and measured a roughly linear temperature gradient averaging 42 °C/km and a maximum bottom hole temperature of 66 °C. This gradient is more than twice the background for Hawai‘i and within a range of gradients measured in this depth range for some exploration wells within the volcanically active East Rift Zone of Kīlauea Volcano. Geothermal gradient determinations and computed chemical geothermometer temperatures indicate that accessible temperatures within Lāna‘i Well 10 are 130–200 °C between 2 and 3 km depth. This paper includes a summary of detailed core logging, which found pervasive hydrothermal alteration. We recommend drilling a slim hole within Lāna‘i's caldera to ∼2 km, where considerably higher temperatures may be encountered. The positive implications this project's results have for the island of O‘ahu are substantial. The shield stage of O‘ahu's volcanoes ended 1–2 Million years earlier, however O'ahu uses more electricity than the rest of the islands combined.

The researches on the hydrogeochemistry of geothermal waters from magma-indirectly related geothermal systems in Yunnan-Tibet geothermal belt (YTGB) mainly focus on major ions and stable isotopes, but the studies of trace elements are limited and the hydrogeochemistry of trace elements is not yet clear, and whether trace elements can be used to reveal the origin of geothermal water still needs to be studied. Therefore, in this article, trace elements (Li, Cs, Rb, Sb, W, V, Cr, Ba, Sr and Mo) in the geothermal waters in the Rehai geothermal system in Yunnan in China, one of the few geothermal systems with acidic geothermal water, are selected to study the source, evolution and enrichment of trace elements combined with the major ions and δ²H and δ¹⁸O isotopes. The results show that the geothermal waters are divided into four clusters and the trace elements are divided into three groups. Group 1 (Li, Cs, Rb, W, V, Sb and Cr) are of magmatic fluid origin and can be used to indicate whether a geothermal system has a magma heat source. Group 2 (Sr and Mo) mainly originate from the incongruent leaching of host rocks and Group 3 (Ba) mainly originates from the mixing with shallow groundwater and the incongruent leaching of host rocks. The hydrogeochemical processes controlling the concentrations of trace elements of each group are discussed, and on this basis, the origin, evolution and enrichment of the trace elements of each cluster are determined. Li, Cs, Rb, Sb, W, V and Cr have the potential the potential to indicate the heat source properties of hydrothermal geothermal systems, but Ba, Sr and Mo do not. Finally, the origin, and evolution model of these trace elements in the RH geothermal waters are established. The research is helpful in understanding the migration and transformation of mass in deep circulation of geothermal water, the characteristics of magmatic water, hydrothermal mineralization, and the comprehensive utilization and development of geothermal resources in similar regions.

Vertical planar installations in shallow ground are uncommon technological variants for geothermal heat supply. Still, they are of increasing interest when depth and space restrictions do not allow the drilling of boreholes or the installation of horizontal collectors. This work is dedicated to plate-shaped closed-loop heat exchangers that are installed in trenches at a few meters depth. A novel three-dimensional analytical model is presented that accounts for the thermal properties as well as seasonal temperature variation in the ground. The model represents the trench collector as a finite plane source with a specific thermal resistance to simulate the mean temperature of the circulating heat carrier fluid. Both, a detailed dimensional analysis and a successful comparison to numerical simulation are presented. Even though only conductive heat transport is simulated, the model could be validated to the conditions observed at an experimental field site with a trench collector installed at Biberach, Germany. The presented analytical method can serve as an ideal tool for the fast dimensioning of vertical planar heat collectors in practice, and it represents a fundamental framework for the integration of advection or latent heat transfer in frozen ground.