Geothermics最新文献

The urgent need to address climate change necessitates a reduction in carbon emissions, particularly within the building sector. To achieve carbon neutrality, innovative technologies such as carbon capture, renewable energy systems, and carbon-neutral materials have been developed. However, there remains a dearth of research quantitatively analyzing carbon emissions through a life cycle assessment while implementing these technologies in real-world building scenarios. Additionally, Ground-source Heat Pumps (GSHPs) demonstrate superior efficiency compared to Air-source Heat Pumps (ASHPs) by leveraging stable ground temperatures, yet their widespread adoption is hindered by high initial investment costs. This study compares and analyzes the carbon emissions of GSHPs with Modular Ground Heat Exchangers (MGHXs), designed to mitigate initial investment barriers, alongside Vertical Ground Heat Exchangers (VGHXs) and ASHPs. The primary objective is to evaluate technology adoption feasibility from a carbon equivalent perspective, focusing on energy demand through building energy simulation. Results indicate that MGHXs exhibit a 6.7 % reduction in carbon emissions compared to VGHXs during production and construction (stage A). However, MGHXs generate 0.57 CO2-eq more per square meter per year during building operation (stage C). The implementation of geothermal energy systems in new buildings across South Korea could potentially achieve a maximum reduction effect of 11.6 % concerning the country's NDC (Nationally Determined Contributions) 2030 carbon reduction target.

Retrieving land surface temperature originating from subsurface thermal data using satellite images has some challenges, especially in tropical areas. The vegetation, cloud cover, and thick soil layers affect the detected ground temperatures. The low-to-medium spatial resolution of thermal infrared images leads to low accuracy compared with ground measurements. Therefore, proper image correction, calibration, and spatial resolution are required for comparison with kinetic temperature measured from the ground. The objective of this study is to detect thermal and vegetation anomalies related to steam spots in subsurface geothermal systems using multivariable thermal infrared corrections and the red band angle of a high spatial resolution optical image, respectively. In this study, the Kamojang–Guntur Volcanic Complex, West Java, Indonesia was selected as the study area. The exploitation and exploration of steam fields were used to assess the accuracy of the proposed method. Thermal infrared images were obtained using an advanced spaceborne thermal emission and reflection radiometer (ASTER). Principal and multivariable corrections were applied to obtain the surface temperature related to steam spots using ground thermal measurements and land cover classification to recognize surface emissivity originating from vegetation, urban areas, bare land, and water bodies. To improve multivariable analyses and interpretations, we used the high spatial resolution image of PlanetScope to obtain vegetation indices from steam spots. The gradient redness index was calculated from the atmospherically corrected PlanetScope image and used as an indicator of ground steam spot signatures. A field measurement campaign was performed to verify and analyze the thermal and vegetation indices at the ground level. Accordingly, we found that the high anomalies of the corrected surface temperature and physiological leaves were concordant with the opened and closed steam spots in the Kamojang–Guntur Volcanic Complex. Thermal and vegetation indices have the potential to estimate hidden geothermal systems and can be used in other similar areas.

The study investigates the performance of an Earth-Air Heat Exchanger (EAHE) system, which uses underground pipes to pre-condition incoming air by leveraging the stable temperatures of the earth, thereby enhancing energy efficiency in buildings. A key challenge in heating applications is the heat loss experienced by air as it exits the pipe, which leads to a temperature drop. This study addresses this issue by exploring the impact of different soil layer configurations on reducing the outlet air temperature drop. A numerical analysis was conducted, to simulate various arrangements of soil layers to determine their effect on the outlet air temperature. The soils used include typical soil and sand-bentonite mixtures with moisture contents of 0 %, 10 %, and 20 %. The results indicate that the optimal configuration consists of two layers: an upper layer of one meter of dry typical soil and a lower layer of wet sand-bentonite soil with 20 % moisture content. This configuration yields an outlet air temperature of 20.2˚C, representing a 15.9 % increase compared to a single-layer model. This study provides novel insights by demonstrating that specific soil layer arrangements can significantly enhance the thermal performance of EAHE systems, offering a potential solution to minimize temperature drops in heating applications.

The Puga valley, in Ladakh, contains one of India's most prospective geothermal systems. Substantial geophysical and geochemical research has been conducted to characterise this system, though uncertainties regarding the subsurface reservoir's geometry and permeability structure remain a barrier to its development. In this contribution, we aim to fill some of these knowledge gaps by integrating new geological data and structural analyses with previously published geochemical and geophysical interpretations, and derive an integrated conceptual model of the geothermal system. Using digital outcrop techniques and field mapping, we identify and characterise several important structures (faults and foliations) that facilitate fluid flow in the otherwise impermeable Tso Morari gneiss. Petrological and field evidence for outcropping hydrothermally altered lithologies, may have formed in a geothermal system analogous to the active one, are also presented. Based on these observations and a simplified finite-element model, we suggest that tectonic and topographic stresses likely control reservoir architecture and connectivity. Lastly, we caution that geomorphological evidence for neotectonic movement on faults at Puga indicate the need for seismic hazard assessment prior to exploitation of the geothermal system, and identify potential parallels between Puga and the Yangbajing geothermal field in China.

In this work, numerical optimization based on stochastic gradient methods is used to assist geothermal operators in finding improved field development strategies that are robust to accounted geological uncertainties. Well types, production rate targets and well locations are optimized to maximize the economics of low-enthalpy heat recovery in a real-life case with stacked reservoir formations. Significant improvements are obtained with respect to the strategy designed by engineers. Imposing fault stability constraints impacts significantly the optimal configurations, with coordinated well rates and placement playing a key role to boost efficiency of geothermal production while keeping stress change effects to acceptable limits.

It is significant to study the mechanical properties of hot dry rock (HDR) for the development of deep geothermal energy. At present, the creep behavior of granite under real-time high temperature is not fully understood. The creep behavior of granite at 25 ∼ 800°C was investigated by real-time high-temperature uniaxial compression and graded load creep tests, and the thermal damage mechanism of granite was studied by scanning electron microscopy (SEM) experiments. The paper systematically analyzes the evolution of mechanical indexes such as uniaxial compressive strength (UCS), elastic modulus, creep deformation, steady creep rate and long-term strength of granite under thermal-force coupling. The results show that the UCS and elastic modulus of granite increase with increasing temperature in the range of 25 ∼ 200 °C, and decrease with increasing temperature in the range of 200 ∼ 800 °C. The damage speed of granite is the fastest in the temperature range of 400 ∼ 600 °C. The steady creep rate of granite increases with the increase of temperature and stress level. The ratio of long-term strength to UCS decreases with increasing temperature, from 93.6% at 25 °C to 73.2% at 800 °C. The research results provide relevant thermal damage mechanical parameters and theoretical basis for the development of HDR.

The numerical assessment of Micro Energy Piles (MEPs) to enhance foundation bearing capacity (Q_u) and cooling efficiency of 400-kV transformers is followed by economic evaluations. Findings show that increasing temperature-differential, MEP length, grout cohesion, and especially MEP diameter can increase Q_u by 6–29 %, 25 %, 22–26 %, and 96–123 %, respectively. Optimal MEP configurations are recommended based on economic viability across different soils, with higher heat-exchange rates and grout cohesion yielding cost-effective solutions. Exploring viable options to improve Q_u and cooling power demonstrates that utilizing MEPs is 26 % and 31 % more cost-effective than energy piles and helical energy piles, respectively, under comparable conditions.

The content of metasilicic acid in geothermal water is usually high. In this paper, the hydrochemical composition of hot springs and geothermal wells from different lithologic aquifers was studied by End-member mixing analysis, and the source and influencing factors of the H₂SiO₃ concentration in geothermal water were revealed. The results show that the H₂SiO₃ concentration in geothermal water is almost independent of the lithology of the surrounding rock at surface of hot springs and geothermal wells. Temperature is an important control factor in the H₂SiO₃ concentration of hot springs and geothermal well waters. The metasilicic acid in geothermal water mainly comes from the geothermal source water, and the mixing of a large proportion of cold water will dilute the metasilicic acid, resulting in a relatively large variation in hot springs and geothermal well waters. The mixing process evaluation gives a good overview of the fluid flow (reservoir temperature and circulation depth) within the region.

The Canarian archipelago comprises seven major oceanic volcanic islands located off the northwest coast of Africa. Due to recent volcanic activity, the Canary Islands boast significant high enthalpy geothermal potential. Extensive soil gas surveys, combined with magnetotelluric and ambient noise tomography studies for geothermal exploration, have been conducted on the island of Tenerife (Canary Islands). The findings from these studies have highlighted the necessity of undertaking detailed surface exploration work in areas with the greatest geothermal potential.

Here we present the findings from a comprehensive soil gas survey (∼500 sampling sites/km²) conducted in a 0.7 km² area known as Madre del Agua on the Tenerife north-south rift zone (SRZ) volcano, where surface geothermal features are not readily apparent. The selection of the study area followed a preliminary low-density soil gas survey (5 sampling sites/km²) and a magnetotelluric survey, which indicated a thinning of a broad-scale clay alteration cap. At each of the 362 sampling sites, measurements of soil CO₂ efflux and ²²²Rn activity were conducted in situ. Additionally, soil gas samples were collected at a depth of 40 cm for further chemical and isotopic analysis (δ¹³C-CO₂). Statistical-graphical analysis and the assessment of spatial distribution of the soil physico-chemical data confirms the presence of a relative enrichment of deep-seated gases in the soil gas atmosphere. The detection of these soil gas anomalies holds potential for identifying permeable areas and possible upwelling or boiling zones.

In stratified porous media, non-uniform velocity between layers combined with thermal conduction across layers causes spreading of the thermal front: thermal Taylor dispersion. Conventional upscaling not accounting for this heterogeneity within simulation grid blocks underestimates thermal dispersion, leading to overestimation of thermal breakthrough time. We derive a model for effective longitudinal thermal diffusivity in the direction of flow, α_eff, to represent the effective thermal dispersion in two-layer media. α_eff, accounting for thermal Taylor dispersion, is much greater than the thermal diffusivity of the rock itself. We define a dimensionless number, N_TC, a ratio of times for longitudinal convection to transverse conduction, as an indicator of transverse thermal equilibration of the system during cold- or hot-water injection. For N_TC > 5, thermal dispersion in the two-layer system closely approximates a single layer with α_eff. This suggests a two-layer medium satisfying N_TC > 5 can be combined into a single layer with an effective longitudinal thermal diffusivity α_eff. In application to a geothermal reservoir, one can apply the model to perform upscaling in stages, i.e. combining two layers satisfying the N_TC criterion in each stage. The α_eff model accounting for the fine-scale heterogeneity within simulation grid blocks would enhance the prediction accuracy of thermal breakthrough time and thus thermal lifetime.