Geothermics最新文献

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.

Subsurface reservoir temperature of a geothermal province is popularly estimated using various geothermometers but it is necessary to examine the suitability of them. Present work studies the performances of five popular geothermometers Na-K, Na-K-Ca, Quartz, Chalcedony and K-Mg to forecast the reservoir temperature of 148 geothermal springs located in different parts of the world. The predicted temperature of the geothermometers have been compared with the bottom whole temperature (BHT) of the wells drilled in those geothermal fields to check the accuracy of the predictions.

The results show that performance of a particular geothermometer is significantly affected by the type of rocks in a geothermal reservoir. Na-K geothermometer provides highest accuracy for the basaltic and sandstone reservoir rocks with average errors 15 % and 11 % respectively. The quartz geothermometer also provides almost equally good prediction for sandstone. The best result for a granitic reservoir rock is obtained by Na-K-Ca with an average error about 15 %. The carbonate reservoir rocks are the most difficult reservoir rock to use any geothermometer as lowest error of prediction using any geothermometer is about 26 %. The chalcedony performed the poorest among all geothermometers and is not recommended for any reservoir rock types under considerations. Thus, the study on global geothermal fields shows that the reservoir rock type must be considered to select a geothermometer else it may cause very high error in prediction of reservoir temperature. However, none of the geothermometer could produce error less than 10 %. It is worth noting that the present study though establishes the suitability of a geothermometer for a particular lithology, it does not explore the rationale for such a suitability.

The Alpehue Hydrothermal Field (AHF) near the Sollipulli Volcano in the Southern Volcanic Zone of Chile shows promise as a significant geothermal resource. A comprehensive geothermal exploration survey was conducted, including the evaluation of hydrothermal gases, geothermometer calculations, and CO₂ flux measurements, to assess the AHF's geothermal potential. Our results indicate that the hydrothermal gasses at the AHF primarily originate from primitive, mantle-derived sources, with some contribution from crustal sediments. Two different CO₂ populations of fluxes were identified. One corresponds to the background emission related to the soil biological activity (mean ∼7.7 g·m⁻²·d⁻¹), and the other, much more significant, emanates from an endogenous source related to the Alpehue hydrothermal reservoir (mean ∼461 g·m⁻²·d⁻¹). Reservoir temperatures were calculated using gas geothermometry yielding average temperatures of 249 °C. The calculated heat flow rate of the AHF is approximately 3.3 MW and the heat flux corresponds to 156 thermal MW⋅km⁻², which could be considered a medium geothermal potential comparable to other systems worldwide. Although further studies are needed to fully address its exploitability, this study presents favorable characteristics of the AHF that make it a promising avenue for further exploration.

Investigating hydrogeochemistry in geothermal fluids is a valuable approach to comprehending the intricate process of deep geothermal water circulation and uncovering the underlying mechanism behind the formation of geothermal systems. The article presents a thorough investigation of the hydrogeochemical and stable isotope characteristics of geothermal fields situated on both the southern and northern sides of the Xi'an depression. This study elucidates the process and progression of deep geothermal water, thereby offering theoretical backing for the exploitation of geothermal resources in the Weihe Basin. The data indicates the following points. The predominant chemical composition of geothermal water consists of SO₄·HCO₃–Na and SO₄·HCO₃·Cl–Na types. The ionic components are mainly impacted by the dissolution of Silicate and evaporite minerals, as well as the alternating adsorption of cations. The geothermal water is replenished by rainfall from the Qinling Mountains, with the recharge elevation varying from 677.94 m to 1,467.65 m. Various techniques are employed to determine the temperature and depth of the reservoir, which helps to understand the behavior of the deep thermal water. Thus, the study determines that the geothermal water in the Xi'an depression originates from laminar-controlled geothermal reservoirs, lateral flow recharge, and an unusual deep thermal structure.