Exploration Of Geothermal Resources Research Articles

A Study on the Acquisition Technology for Weak Seismic Signals from Deep Geothermal Reservoirs

There are rich geothermal resources in China and they are widely distributed. After years of continuous exploration and production, most of the shallow geothermal resources have been explored and the current exploration mainly focuses on deep ones. Among a great many geophysical exploration methods, seismic survey is the most effective means of geothermal resource exploration and production, but its weak seismic reflection signal, low S/N ratio and poor imaging of thermal reservoirs due to the seismic geological conditions restrict the production and utilization of deep geothermal resources. It considers through the analysis of the geophysical characteristics of the thermal reservoir that the main causes for the weak seismic reflection signals from deep thermal reservoirs are (1) the shielding effect of the strong wave impedance interface between the thermal reservoir and the caprocks; (2) the small reflection coefficient inside the thermal reservoir; and (3) the serious absorption and attenuation of high-temperature fluids such as hydrothermal fluids and steam in the thermal reservoirs by seismic waves. Accordingly, a series of seismic data acquisition technologies are proposed based on the high-precision vibroseis low-frequency shooting, high-sensitivity geophones long-spread receiving and small bin size highfold technologies, and their application in the seismic acquisition of dry-hot rocks (HDR) in Gonghe Basin, Qinghai, shows a very good application effect.

Preface

ITB International Geothermal Workshop 2022 was an event organized by ITB Geothermal Master Program which was held on August 2 – 4, 2022 on an online basis through a live virtual workshop (Webinar) via Zoom and YouTube. Followed by over 2200 participants from many different aspects of the geothermal community, such as academia, industries, and government. This year’s theme is “Geothermal Competitiveness in Supporting Net-Zero Emission: From Technical to Business Model”, which focuses more on the Prospecting and Utilization of Geothermal Energy and collaborating Indonesia Geothermal Stakeholders by inviting speakers from various aspects in geothermal energy.The 11th ITB International Geothermal Workshop is expected to become a melting pot for sharing knowledge, experiences and solving technical and non-technical geothermal issues in Indonesia. For this year’s event, the focus of discussions would be the development and innovation of technology for the exploration, exploitation, and utilization of geothermal resources, socio-economics, green investment, and competitive business models.List of Conference Details, Committee are available in this Pdf.

3-D Inversion of Gravity Data of the Central and Eastern Gonghe Basin for Geothermal Exploration

The Gonghe Basin is one of the most important regions for the exploration and development of hot dry rock geothermal resources in China. However, there is still some controversy about the main heat source of hot dry rock geothermal resources in the Gonghe Basin. Combined with previous research results including three-dimensional magnetotelluric imaging and linear inversion of Rayleigh wave group and phase velocity result, we obtained a high-resolution underground spatial density distribution model of the Gonghe Basin based on satellite gravity data by using 3-D gravity focusing inversion method. According to the results, there are widely distributed low density anomalies relative to surrounding rock in the middle crust of the study area. The low-density layer is speculated to be a low-velocity, high-conductivity partial melting layer in the crust of the Gonghe Basin. The inversion result confirms for the first time the existence of a partial melt layer from the gravity point of view, and this high temperature melt layer may be the main heat source of the hot dry rock geothermal resources in the Gonghe Basin. It can provide a new basis for further research on the genesis of the hot dry rock geothermal system in the Gonghe Basin.

Analysis of geothermal potential in Hangjiahu area based on remote sensing and geographic information system

Geothermal resources are one of the most valuable renewable energy sources because of their stability, reliability, cleanliness, safety and abundant reserves. Efficient and economical remote sensing and GIS (Geographic Information System) technology has high practical value in geothermal resources exploration. However, different study areas have different geothermal formation mechanisms. In the process of establishing the model, which factors are used for modeling and how to quantify the factors reasonably are still problems to be analyzed and studied. Taking Hangjiahu Plain of Zhejiang Province as an example, based on geothermal exploration and remote sensing interpretation data, the correlation between the existing geothermal hot spots and geothermal related factors was evaluated in this paper, such as lithology, fault zone distance, surface water system and its distance, seismic point distance, magmatic rock and volcanic rock distance, surface water, farmland, woodland temperature and so on. The relationship between geothermal potential and distribution characteristics of surface thermal environment, fault activity, surface water system and other factors was explored. AHP (Analytic Hierarchy Process) and BP (Back Propagation) neural network were used for establishing geothermal potential target evaluation models. The potential geothermal areas of Hangjiahu Plain were divided into five grades using geothermal exploration model, and most geothermal drilling sites were distributed in extremely high potential areas and high potential areas. The results show that it is feasible to analyze geothermal potential targets using remote sensing interpretation data and geographic information system analysis databased on analytic hierarchy process analytic hierarchy process and back propagation neural network, and the distribution characteristics of surface thermal environment, fault activity, surface water system and other related factors are also related to geothermal distribution. The prediction results of the model coincide with the existing geothermal drilling sites, which provides a new idea for geothermal exploration.

Thermally Induced Microcracks in Granite and Their Effect on the Macroscale Mechanical Behavior

AbstractUnderstanding the thermal effects on rock is critical for the exploration of geothermal resources and the temperature‐driven evolution of Earth. The macroscale mechanical behavior of granite under thermal loading can be complicated due to microcracking and the heterogeneity of minerals. In this study, the thermally induced microcrack propagation of granite was first observed in real time by an ultrahigh‐temperature instrument on an optical microscope. The previous investigation believed that the α–β quartz transition at approximately 573°C leads to a sharp decrease in macroscale mechanical behavior. However, the present experimental results revealed that microcracks initiate at 300°C and coalesce between 400 and 600°C, which is the main reason for the sharp decrease in macroscale mechanical properties of granite. Additionally, an accurate grain‐based model based on the mineralogical morphology of granite samples adopted mechanical parameters of minerals obtained from microscale rock mechanical techniques. It is able to well reproduce the process of microcracking and the strength evolution of granite during heating. The numerical results show that the heterogeneity of thermal expansion and mechanical properties of minerals produce local thermal stress concentrations in granite. The uneven tensile‐compressive stress between feldspar and quartz and the shear stress around biotite result in the initiation and propagation of microcracks. The present work is potentially useful for understanding and predicting the mechanical behavior of granites under thermal loading with different mineral compositions and microstructures.

Geothermal resource exploration in South America using an innovative GIS-based approach: A case study in Ecuador

Integrating geothermal energy contributes to a sustainable energy transition in South American countries. Geothermal energy is a non-variable and renewable resource that can be used for baseload power generation to reduce the overdependence on fossil fuel and hydropower plants. There is a vast and untapped geothermal potential in South America. Nevertheless, multiple barriers, including lack of geological, hydrogeochemical and geophysical background and outdated regional studies have blocked the development as it should be. Thus, this study aims to update and identify promising areas for further geothermal exploration through a favourability map implemented in a GIS-based model for Ecuador as a case study. The results show that approximately half (49.2%) of the national territory of Ecuador has promising areas to explore and develop geothermal systems along the Andean and South-west coast. New zones were identified, which contribute to increasing the national inventories of geothermal energy. Also, the Northern Amazon region presents mature oil fields and reservoirs close to their productive life. Thus, geothermal energy systems may help transition the petroleum industry into a clean energy provider. This research contributes to the needed improvement of existing geothermal resource inventories. The robustness of the proposed GIS-based model has been tested. Thus, it allows the analysis and combination of available open geodata in an effective, low-cost method, and even under a scenario of scarce data availability, to support decision-makers, researchers, or stakeholders, and guide geothermal exploration programs at a national level.

Genesis of Significance of Carbonated Thermal Water Springs in Xining Basin, China

There are 30 carbonate hot springs in Yaoshuitan geothermal field, Xining Basin, China, with a temperature of 18~41.5 °C; and there are 10 carbonate hot springs in Qijiachuan geothermal field, with a temperature of 10~19.5 °C. Both geothermal fields are carbonate hot springs containing large amounts of CO2 gas. In order to reveal the origin of the carbonated hot springs in Yaoshuitan and Qijiachuan of Xining Basin, this paper offers a comprehensive study of the regional deep geology, tectonic setting, total analysis of carbonated hot springs, δ2H, δ18O, δ13C isotopes, main gas composition, and geochemical characteristics of travertine dating, travertine δ13C, and rare earth elements. The geological process of carbonated hot spring formation and the evolution of H+ content from deep to shallow is revealed, and the genetic mechanism of the carbonated hot spring in Xining Basin is systematically summarized. The results show that: (1) The characteristics of δ2H and δ18O isotopes indicate that the recharge source of carbonated thermal water springs in Xining Basin is mainly atmospheric precipitation. The age of carbonated thermal water springs at 14C is more than 20 ka, indicating that some of them may come from deep fluid (gas) sources. The R/Ra in carbonated thermal water springs is mostly less than 1, indicating that the helium in geothermal water is mainly crustal source helium, and there is no deep mantle source material. (2) The Piper three-plot indicates that the direction of groundwater evolution from the recharge area at the edge of Xining Basin to Yaoshuitan and Qijiachuan carbonated thermal water spring area near the edge of the basin is opposite to the normal path of groundwater evolution in the basin, which is due to the large amount of CO2 gas mixed in the deep fault along the northern margin of Laji Mountain. The ratio of (Ca2+ + Mg2+) and (HCO3− + SO42−) in the Potan and Qijiachuan carbonated thermal water springs is close to 1, and the ratio of (Na+ + K+)/HCO3− is less than 1. It indicates that the chemical composition of the Yaoshuitan carbonated thermal water spring and the Qijiachuan carbonated thermal water spring in Xining Basin is dominated by the dissolution of calcite, dolomite, and gypsum in deep carbonate reservoirs, supplemented by the dissolution of silicate minerals. The relationship between the volume fraction of CO2 and the δ13C value of carbon isotope of CO2 indicates that the source of CO2 is inorganic, which is mainly formed by metamorphism and decomposition of deep carbonate and marble. The δEu < 1 and δCe > 1 of the rare earth elements in the calcium center of the carbonated thermal water springs indicate that the groundwater supplying the travertine material has been in the acidic environment receiving CO2 from the deep crust for a long time. (3) A series of tectonic activities, such as late collision and post-collision between the Indian and Eurasian plates, has led to the uplift, asthenosphere upwelling, and thermal invasion of the northern Tibetan Plateau and other deep dynamic processes. The deep faults in the northern margin of the Laji Mountain and other deep faults with obvious neotectonic activity have provided channels for the up-invasion of deep thermal materials, and local geothermal anomalies were formed near the deep faults. The hidden carbonate rocks and silicate rocks with large thickness undergo thermal metamorphism under high temperature and high pressure in the deep geothermal anomaly area and form a large amount of CO2, which is dissolved in water and enhances the acidity of water. At the same time, the dissolution reaction of acidic water to carbonate rocks consumes H+, which keeps the carbonated thermal water spring weakly acidic. (4) The composition of travertine in carbonated thermal water springs is dominated by calcite, indicating that travertine may be formed in a deep geological environment with a temperature of 150~200 °C, indicating that there are abnormal heat sources in shallow carbonate strata with a burial depth of 3000~4000 m. The abnormal heat source may be caused by the deep fault in the northern margin of Laji Mountain, as well as other deep and large faults channeled in the deep crust and mantle heat source, indicating that the deep fault in the northern margin of Laji Mountain has an obvious heat-controlling effect, and there is a good prospect of geothermal resources exploration near the fault.

Characteristics of Radiogenic Heat Production of Widely Distributed Granitoids in Western Sichuan, Southeast Tibetan Plateau

Abstract Investigating the genesis of geothermal resources requires a thorough understanding of the heat source mechanism, which is also a vital basis for the efficient exploration and utilization of geothermal resources. Situated in the eastern Himalayan syntax, western Sichuan is considered to be one of the main concentration regions of high-temperature geothermal resources in China. To date, various studies have been carried out to reveal the heat source and genesis of the abundant high-temperature resources in this area; however, studies on the contribution of the radioactive heat generated by the widely distributed granitoids to the high-temperature geothermal resources remain scarce. In order to resolve this knowledge gap, we attempted to obtain evidence from the geochemical data published in the literature in the past few decades. A total of 548 radiogenic heat production rate data were determined. The statistical data indicate that the average concentrations of the heat-producing elements U, Th, and K are 6.09±5.22 ppm, 26.74±16.78 ppm, and 3.51±0.82%, respectively. The calculated heat production values of the granitoids vary from 0.52 to 10.86 μW/m3, yielding an arithmetic average value of 3.74±2.15 μW/m3, which is higher than that of global Mesozoic–Cenozoic granites (3.09±1.62 μW/m3). Based on the heat production values, the capacity of the granitic batholiths to store heat was assessed, and the Dongcuo pluton was found to be the largest heat reservoir (382.88×1013 J/a). The distribution of the crustal heat flow was examined using the calculated heat production data and the stratigraphic structure obtained via deep seismic sounding in the study area. The results indicate that the crustal heat flow is 48.3–56.2 mW/m2, which is mainly contributed by the radioactive decay in the granitoids in the upper crust. The fact that it accounts for nearly half of the regional background heat flow indicates that the radiogenic heat from the granitoids is an important heat source for the formation of the thermal anomaly and the high-temperature geothermal resources in the study area. Thus, the results obtained in this study highlight the importance of the widely distributed granitoids to high-temperature geothermal resources in western Sichuan.

Ground surface temperature monitoring data analysis and applications to geothermal exploration in volcanic areas, Mount Meager, western Canada

The southern Mount Meager area has been studied for its geothermal resource potential for a half century. Although attempts to commercialize the resource were unsuccessful in the past, a large volume of surface and subsurface geoscience data have been collected and made publicly available, making the Mount Meager area a unique natural laboratory for testing new ideas or tools for geothermal exploration. This study investigates the potential of using a ground surface temperature (GST) monitoring network as a tool in geothermal resource exploration. Twenty-two temperature data loggers were deployed in, and surrounding, the core area of the geothermal prospect for nearly one year. The collected temperature time series were analyzed statistically, and machine learning methods such as hierarchical clustering and k-means classification, were applied to data interpretation. The temporal variation of measured temperature can be divided into four segments: 1) snow free, 2) snow affected, 3) snow curtain, and 4) snow melt seasons. The intensity of daily ground temperature variation in the snow free season shows clear environmental and topographic footprints and is complicated by soil properties. The sites with a short period of near zero GST during the snow curtain period is spatially coincident with high heat flow areas. The measured mean GST shows a close affinity with subsurface heat flow and shallow ground water circulation, suggesting that GST time series contain information indicative of subsurface geothermal anomalies and that a GST monitoring network could be an effective tool for geothermal resource exploration in high latitude and/or elevation areas with seasonal snow cover.

Exploration of Geothermal Resources Utilizing Geophysical and Borehole Data in the Abu Gharadig Basin of Egypt’s Northern Western Desert

The Abu Gharadig Basin is regarded as one of the most essential in Egypt, serving as the country’s second most important reservoir for hydrocarbon production. Our present study is focused on the investigation of geothermal resources in the Abu Gharadig Basin. Using airborne magnetic and gravity surveys, as well as temperature well records, we can identify possible geothermal sources in this region. Power spectral analysis was used on the airborne magnetic measurements to compute the Curie Point Depths (CPDs) and display the temperature gradients and heat flows regime in the study area, while on the gravity data, 3-D density inversion was used to identify the basement surface. Real data from bottom-hole temperature (BHT) logs and geological data (structural and stratigraphic data from prior studies) were used to cross-validate the geophysical maps and to ascertain the stratigraphy and structural setting beneath the study location. The depth of the basement rock, according to the studies, ranges from 4.5 to 7 km, and the CPDs run from 17 to 22 km. Furthermore, the estimated temperature gradients vary from 25 to 34 degrees Celsius per kilometer, whereas the heat flows vary from 52 to 86 mW/m2. Generally, there is a correlation between shallow curie depths, uplifts on basement rocks, and sites of high heat flow, indicating that basement rocks are primarily accountable for the geothermal potential of the basin.

3D thermal model of Sicily (Southern Italy) and perspectives for new exploration campaigns for geothermal resources

Quantification of the subsurface geothermal potential primarily relies on the assessment of the thermal and mechanical configuration of the lithosphere. Such investigations require a detailed knowledge of the geological and tectonic forcing on the regional thermal, stress and hydraulic regimes and their counter feedback mechanisms. This approach becomes even more relevant in complex and active tectonic settings. In this regard, the Sicily region, which is located in the Central-Western Mediterranean, is an exceptional case study due to its almost unexplored geothermal potential hosted in a complex geodynamic setting. The present-day geological configuration resulted from the collision between the African and European plates, which led to the coexistence of compressional phases, beginning with the Oligocene-Miocene clockwise rotation of Corsica-Sardinia and alternated extensional phases in the Tyrrhenian basin due to the southward progression of the Sicilian-Maghrebian chain towards areas of the internal foreland (Hyblean domain). In this study, we attempt a reconstruction of the present-day lithospheric state of Sicily to quantify its thermal regime at shallow and intermediate depths. We have carried out a 3D lithospheric-scale gravity modelling in order to define the main geological units and their lithology-dependent rock properties, then integrated into a 3D geological model consistent with available borehole and seismic datasets. We have used the constructed geological model with its lithology-dependent density, thermal conductivity, and radiogenic heat production to derive the present-day conductive thermal field as a whole and for individual tectonic or geological units, thereby considering different boundary conditions. We have finally validated results of the modelling against a shallow temperature dataset derived from hydrocarbon explorations. Our results indicate that the thermal field at depths shallower than 10 km is largely controlled by variability in sedimentary thickness in the foreland and the orogen, while deeper temperatures are primarily controlled by the distribution of the heat transferred from the mantle together with the radiogenic contribution of the shallow crystalline basement rocks and deeper crustal layers. The thermal modelling portrays a rather heterogenous Moho heat flow, locally higher than 80 mW/m2, revealing a particular geodynamic setting with specific areas characterized by high-to-medium enthalpy geothermal potential. As such, our modelling provides new perspectives for the exploration of geothermal resources in Sicily and helps to better constrain the thermal structure of the complex Sicilian collisional setting.

High-temperature hydrothermal resource exploration and development: Comparison with oil and gas resource

The exploration, drilling, and development of high-temperature hydrothermal geothermal resources usually borrow ideas from the oil and gas industry. However, some techniques in the oil and gas industry are not entirely applicable for geothermal resources due to the difference in geological conditions and exploitation objectives. This paper briefly compared and analyzed the differences between high-temperature hydrothermal resources and oil & gas resources in exploration, drilling, and reservoir engineering to improve subsequent hydrothermal exploitation efficiency. The exploration of geothermal resources aims to identify high-temperature rock/fluid, and the improved electromagnetic method is mostly adopted to identify geological structures around geothermal resources due to its low cost. As for the seismic exploration primarily used in the oil & gas industry, it is difficult to interpret the rock associated with high-temperature geothermal activity, except of the high cost and time-consuming. Different from oil and gas wells, geothermal wells have large borehole radii and high requirements for casing corrosion resistance. Low-density drilling fluid is often used due to the lost circulation. Open holes with liner mostly complete conventional geothermal wells. For the dynamic development of geothermal resources, well test in the oil and gas industry can be used, but the material balance and empirical method in oil reservoir engineering are no longer suitable for dynamic analysis of geothermal resource development, and the real-time numerical simulation combined with field data is a more effective method for geothermal resource development.

Seismic Geothermal Resource Exploration based on CPU/GPU Collaborative Parallel Prestack Time Migration

AbstractGeothermal resources exist in complex and comprehensive geological settings. In the current study, we proposed a CPU/GPU collaborative parallel prestack time migration methodology for geothermal resource exploration. First, seismic geological conditions in Xian County were obtained based on an analysis of drill cores for further seismic evaluation. Then, combined with the analysis of two‐dimensional seismic data in the adjacent area, a test section with three seismic survey lines were designed to explore the geological structure of the study area. In the study area, the seismic data were derived through the multiple coverage reflection wave exploration method with explosive ignition in deep wells and high coverage frequency observations. Finally, we employed CPU/GPU collaborative parallel prestack time migration technology to analyze the obtained seismic data for geothermal resource evaluation. The favorable areas of karst fissure heat storage in Middle–Upper Proterozoic Jixianian and Paleozoic Cambrian–Ordovician rocks were inferred together with two preferred recommended exploration holes.

3D S-wave velocity structure of the Ningdu basin in Jiangxi province inferred from ambient noise tomography with dense array

The Ningdu basin, located in southern Jiangxi province of southwest China, is one of the Mesozoic basin groups which has exploration prospects for geothermal energy. A study on the detailed velocity structure of the Ningdu basin can provide important information for geothermal resource exploration. In this study, we deployed a dense seismic array in the Ningdu basin to investigate the 3D velocity structure and discuss implications for geothermal exploration and geological evolution. Based on the dense seismic array including 35 short-period (5 s-100 ​Hz) seismometers with an average interstation distance of ∼5 ​km, Rayleigh surface wave dispersion curves were extracted from the continuous ambient noise data for surface wave tomographic inversion. Group velocity tomography was conducted and the 3D S-wave velocity structure was inverted by the neighborhood algorithm. The results revealed obvious low-velocity anomalies in the center of the basin, consistent with the low-velocity Cretaceous sedimentary rocks. The basement and basin-controlling fault can also be depicted by the S-wave velocity anomalies. The obvious seismic interface is about 2 ​km depth in the basin center and decreases to 700 ​m depth near the basin boundary, suggesting spatial thickness variations of the Cretaceous sediment. The fault features of the S-wave velocity profile coincide with the geological cognition of the western boundary basin-controlling fault, which may provide possible upwelling channels for geothermal fluid. This study suggests that seismic tomography with a dense array is an effective method and can play an important role in the detailed investigations of sedimentary basins.

Paleoenvironment of Mesoproterozoic Gaoyuzhuang and Wumishan Formations, North China: New Insights from Geochemistry and Carbon and Oxygen Isotopes of Dolostones

The Mesoproterozoic Gaoyuzhuang and Wumishan Formations are major geothermal reservoirs in the Hebei Province, North China. Compared to the exploration of geothermal resources and heat-controlling structures, carbon and oxygen isotopic records of the two formations are limited. Here, we present integrated field, petrological, geochemical, carbon, and oxygen isotopic data of carbonate rocks from the Gaoyuzhuang and Wumishan Formations. The Wumishan Formation is characterized by higher CaO and MgO contents and lower SiO2 contents than the Gaoyuzhuang Formation, indicating that the source of the Wumishan Formation likely contains less terrigenous clastic materials. The two formations have low total rare earth element contents, similar to marine carbonate rocks. They show different Eu and Ce anomalies, Al/(Al + Fe + Mn) and Fe/Ti ratios, and (Co + Ni + Cu) contents. They generally show similar carbon isotopic compositions, whereas the carbonate rocks of the middle-upper Gaoyuzhuang Formation show lower δ18O values than the samples from the Wumishan and lower Gaoyuzhuang Formations. These data suggest that the two formations have experienced different transgressive–regressive cycles and that their sedimentary environments varied and were unstable in different sedimentary periods. The middle-upper Gaoyuzhuang Formation was likely affected by hydrothermal fluids, whereas the Wumishan Formation is composed of normal seawater deposits. Integrated evidence reveals that both of the Mesoproterozoic Gaoyuzhuang and Wumishan Formations were deposited in rift environments caused by the breakup of the Columbia/Nuna supercontinent.

Geothermometry in High-Temperature Reservoirs of the Geothermal Springs in Southern Thailand: Insights from Cations and Silica Geothermometers

Geothermal springs have provided a unique opportunity to study the geothermal system of geological processes. A reservoir temperature estimation based on the chemical geothermometers is vitally essential for assessing the exploration and development of geothermal resources. The paper represents the various techniques of geothermometers with comparisons between the silica (quartz and chalcedony) and the cation geothermometers (Na–K–Ca and K–Mg) for the high exit temperature (temp. ≥55°C) of geothermal springs in southern Thailand. The Na–K–Ca geothermometer presented more elevated reservoir temperatures than the K–Mg, silica and chalcedony geothermometers, about 20–30◦C. The preliminary assumed difference between the geothermometers may indicate that the shallow subsurface conditions are mixed with groundwater

Processing Method of Soil Temperature Time Series and Its Application in Geothermal Heat Flow

Nowadays, geothermal resources have become one of the important means for mankind to solve global energy problems and environmental problems, and the exploration and development of geothermal resources are of great significance for sustainable development. However, in view of the complex geological background of the plateau region, the number of heat flow measurement points in this area is small or even blank, thus becoming an important factor limiting the exploration of geothermal resources in this region. In this article, a new model based on Fourier analysis and heat conduction principle is established to process and analyze the long-term monitoring data of soil temperature and eliminate the influence of temperature change on soil temperature as far as possible, so as to improve the calculation accuracy of soil conduction heat dissipation. The experimental results show that the fluctuation range of soil temperature at 20 cm before the correction was large, and the fluctuation range was 2.58°C–14.284°C, which was because the soil here was closer to the land surface and was affected too much by the temperature fluctuation, and as the soil depth deepened, the temperature fluctuation slowly became smaller, and the fluctuation range was 6.67°C–11.15°C at 50 cm, but the effect of temperature fluctuation was still obvious. Also, the fluctuation range was basically reduced within 0.3°C after temperature correction. In this method, the thermal diffusion coefficients of the soil at different depths can be obtained, and the calculated temperatures at the corresponding depths can also be obtained, which can be used to infer the approximate ground temperature gradient of the measured area. This study aims to develop a convenient and fast model for processing soil temperature time series and to provide technical support for developing geothermal resources in highland areas or assessing the geothermal potential of the region.

Genetic Analysis of Geothermal Resources in Deep-Seated Fault Area in Tonghe County, Northeast China and Implications of Geothermal Exploration

Northeast China is an area with high energy consumption and high carbon emissions, and the utilization of geothermal resources can effectively overcome these problems. However, there are few geothermal manifestations in Northeast China and no systematic method for geothermal exploration at present, which hinders the utilization of geothermal resources. Here, a systematic analysis, including hydrochemistry, petrology, isotopes, controlled source audio magnetotelluric sounding, drilling, and temperature curve of two boreholes was carried out to investigate the genesis of geothermal resources in Tonghe County, Northeast China, along the Yilan-Yitong lithospheric fault (YYF). We found that the geothermal water is alkaline Na-HCO3 type water, is of local meteoric origin, and is recharged from the hilly area with an elevation of ~280 m around the study area. We established a geothermal water circulation path model: (1) cold water infiltrated along the YYF to a depth of 2–3 km, (2) cold water was heated by mantle heat, and (3) hot water was stored in sandstone/siltstone, forming a sandstone geothermal reservoir with a temperature of ~70 ℃. These results have important guiding significance for the scientific exploration of geothermal resources in Northeast China.

The Geothermal Artificial Intelligence for geothermal exploration

Exploration of geothermal resources involves analysis and management of a large number of uncertainties, which makes investment and operations decisions challenging. Remote Sensing (RS), Machine Learning (ML) and Artificial Intelligence (AI) have potential in managing the challenges of geothermal exploration. In this paper, we present a methodology that integrates RS, ML and AI to create an initial assessment of geothermal potential, by resorting to known indicators of geothermal areas namely mineral markers, surface temperature, faults and deformation. We demonstrated the implementation of the method in two sites (Brady and Desert Peak geothermal sites) that are close to each other but have different characteristics (Brady having clear surface manifestations and Desert Peak being a blind site). We processed various satellite images and geospatial data for mineral markers, temperature, faults and deformation and then implemented ML methods to obtain pattern of surface manifestation of geothermal sites. We developed an AI that uses patterns from surface manifestations to predict geothermal potential of each pixel. We tested the Geothermal AI using independent data sets obtaining accuracy of 92–95%; also tested the Geothermal AI trained on one site by executing it for the other site to predict the geothermal/non-geothermal delineation, the Geothermal AI performed quite well in prediction with 72–76% accuracy.

A new approach to estimate and delineate the geothermal gradient of Iran

In spite of numerous deep wells drilled for oil, gas, deep water and geothermal purposes, and several local geothermal studies carried out using geochemistry analysis in Iran, lack of a comprehensive geothermal map is palpable. In this paper, nominated reliable surface and subsurface thermal data are gathered, examined and corrected to be involved in mapping process. In order to do so, 107 drilled wells accompanying with geothermal gradient data extracted from geothermometry analysis (available in hot springs) were nominated based on data quality and a proper dispersion. All selected points were evaluated and eventually, a real temperature gradient together with a temperature log were calculated in every location. Therefore, convergent interpolation technique was applied to estimate and distribute the temperature data points to the whole surface. According to the final proposed map, geothermal gradient is increased around geologically active areas such as quaternary volcanoes and active faults such that it is evidently possible to segregate high gradient areas into two major parts including volcano-related and active-fault related areas. Approximate average geothermal gradient in non-volcanic basins like Zagros, Kopet-dagh, central Persian Gulf, Qom, Moghan and Zabol regions are determined as 21 °C/km, 30 °C/km, 31.5 °C/km, 26.7 °C/km, 30 °C/km and 25 °C/km respectively and it reaches to about 149 °C/km around volcanic areas like Sabalan stratovolcano. Undertaken comprehensive survey will be of great assistance in future exploration of geothermal resources in Iran land.