Geothermal Survey Research Articles

Forecasting regional in-situ thermal conductivity of soil based on tree-based ensemble learning

Borehole heat exchanger is essential component in ground-source heat pumps (GSHPs) for developing geothermal energy, where device efficiency depends on the thermal conductivity of soil. Although the thermal response test is generally used to measure this parameter, its time-consuming and susceptibility to test conditions can impact the accuracy of the test. To address this issue, the study conducted shallow geothermal surveys to establish a comprehensive dataset, enabling the construction of the in-situ thermal conductivity predictive model. By selecting seven input features, four classic tree-based ensemble learning models and stacking algorithms were used. Among all the post-tuned models examined, XGBoost-RF emerged as the standout performer, boasting an impressive R2 value of 0.9809 along with the lowest RMSE and MAE. Notably, it demonstrated generalization capabilities, with errors consistently staying within 5 % during the validation process. Additionally, the SHapley Additive exPlanations (SHAP) was used to enhance the interpretability of the model. Among these, the weighted thermal conductivity of the geotechnical was the most influential feature, while groundwater conditions such as permeability coefficient and aquifer thickness were also significant factors. This study provides a rapid and precise prediction of regional in-situ thermal conductivity. It leads to effective decision-making in the design stage of GSHPs.

Technique and results of determination of vertical variations in rock thermal properties, temperature gradient and heat flow

The paper describes the results of experimental geothermal studies of the formation surrounding Savitskaya-300 well (depth 3555 m) drilled in the Volga-Ural oil and gas basin (Orenburg region, Russia). The work was aimed, firstly, at obtaining geothermal data for basin modeling and, secondly, at improving the instrumental and methodological foundations of experimental studies. Continuous core profiling of the rock thermal conductivity, volumetric heat capacity, and thermal anisotropy was performed on all 2886 recovered core samples with the total length of 329.1 m. Additional measurements were conducted at fluid saturation and elevated temperatures. For non-cored intervals, the rock thermal properties were determined from well-logging data and via measurements on rock cuttings. The studied formation is characterized by high thermal heterogeneity at both the level of strata (horizons) and individual samples. Significant thermal anisotropy up to 1.50–1.66 in the lower part of the well has been observed. To obtain data on vertical variations of equilibrium temperature and its gradient, temperature logging was performed 7 times within the 2 to 186 days of well shut-in. New data on the recovery of temperature and its gradient after drilling are important for the practice of applied and fundamental geothermal surveys. A significant increase in heat flow with depth was established based on the results of temperature gradient and rock thermal conductivity determination for 34 depth intervals. The observed general vertical variation in the whole depth range of the well up to ∼3.3 km depth can be attributed to paleoclimatic effect in the Late Pleistocene-Holocene, while the sharp increase in heat flow at ∼3.3 km within Fransian sediments is possibly due to advective heat transfer by fluid filtration. The apparent heat flow was established to be 84.3 mW⋅m−2 in the lower section of the well, below 3.3 km. The value may be close to the steady-state heat flow value, which is 84% higher than the previous published average data for the studied area.

Survey on Geothermal Resources in Zhangjiakou Area

The Zhangjiakou area is rich in geothermal resources, and many counties in the region have discovered low-temperature geothermal. Structurally, Huailai County, Zhangjiakou City is located at the intersection of Zhangjiakou-Penglai Fault Zone and Shanxi Fault Basin (or Fenwei Seismic Tectonic Zone), namely the Yanqing-Huailai Basin (Yanhuai Basin). A large amount of geothermal resource investigation and research works has preliminarily defined that the area has good geothermal resource accumulation conditions. From 2019 to 2020, the China Geological Survey has organized several investigation and research in the area for in-depth geothermal resource. As one method of the survey results verification, a parameter well for geothermal resource survey was deployed as ZK02 and completed at 3000m depth. The ZK02 well was completed at a depth of 3006.9m, drilling through the Quaternary, Neogene, and Jixian strata, and entered the Archean gneiss strata. The well successfully explored high-quality artesian heat storage in the Jixian strata, obtained deep geothermal geological data and physical data, revealed the regional stratigraphic sequence and geological structure characteristics, and provided a scientific basis for regional geothermal resource potential evaluation. Based on the engineering practice of ZK02 well, this paper systematically summarizes drilling technology and experience from well structure to drilling equipment, construction technology and key technology, analyses the complex conditions and countermeasures downhole, and provide reference for the follow-up regional geothermal resources investigation, research and development and.

Volcanological context of the Bouillante high temperature geothermal system, Guadeloupe, Lesser Antilles

The hydrothermal manifestations of Bouillante area (Guadeloupe, Lesser Antilles) motivated a geothermal survey in the sixties. Nevertheless, the heat source of the Bouillante hydrothermal system is still debated: (i) local magma body, (ii) magmatic source beneath the centre of the island or (iii) result from the deep circulation.Several arguments support the first hypothesis and the definition of a specific volcanic series, the « Bouillante chain », according to the following characteristics:➢ location: small monogenic volcanoes are scattered along the Caribbean coastline, on- and off-shore;➢ structural control: volcanic centres have developed at the junction of two regional tectonic systems, the NNW-SSE trending Montserrat - Les Saintes fault and the sub-E-W trending Marie-Galante’s grabens system;➢ dynamics: their products often result from a magma - water interaction between, either in an external or internal hydromagmatism;➢ petrology: specific magmatic trend reached an extreme (rhyolitic) level by crystal fractionation.The links between the Bouillante chain and contemporary / neighbouring other Guadeloupe volcanic formations (Les Mamelles domes, Axial chain, Caraïbes mountains, Grande Découverte volcano) are discussed but partly remain to be specified.

Geomechanical modelling of a Geothermal reservoir in Tanzania

Countries that are favored by being situated within the East African Rift System, Tanzania is among them. Geothermal energy is a potential renewable source that should be taken into account in Tanzania’s energy mix. Computational Fluid Dynamic (Mathematical modeling and numerical simulation) are taking into account for predicting of geothermal reservoir. Preliminary, geothermal survey studies have been done in Tanzania. However, the available data is inadequate partly because of limitations in traditional measurements and visualization techniques for the geothermal reservoirs located deep underground. This paper presents computational fluid dynamics (CFD) technique which has been employed to address the limitations by giving an insight into these complex flows that are often difficult, expensive or impossible to study using traditional techniques. The discretized Euler-Eulerian equations are solved in Fluent 12 software for the conservation of mass, momentum, energy and species. The predicted results indicate that thermodynamic properties such as the rate of temperature and pressure drop along the fractured porous rock (hole path) in the concerned study area were 0.02°C per meter and 0.025 bar per meter, respectively. Further, the predicted steam quality at outlet is 0.9.

吾妻火山一切経八幡焼の地熱調査 : 1977年集中観測 : 日本火山学会1980年度春季大会

吾妻火山一切経八幡焼の地熱調査 : 1977年集中観測 : 日本火山学会1980年度春季大会

日本の地熱資源ポテンシャル調査への空中物理探査の適用性

日本国内の地熱資源ポテンシャルの調査に，空中重力偏差法探査，時間領域空中電磁探査および空中磁気探査を適用した。空中重力偏差法探査により詳細な探査結果が得られ，熱源となる可能性がある貫入岩を示唆するような高鉛直重力偏差異常の近傍に，地熱貯留層を発達させる断裂系に関連する可能性のある線状あるいは環状の重力偏差リニアメントが示された。空中電磁探査で得られた低比抵抗異常と空中磁気探査で得られた低磁気異常が地熱兆候の指標である帽岩や熱水変質帯の分布を示唆しているケースがあることも示された。これらの空中物理探査で得られた個々の物性指標は必ずしも地熱兆候を示唆するものとは限らないが，物性指標が重複する場所は地熱資源ポテンシャルが高いと考えられる。これらの結果に坑井での温度情報を利用した温度構造を組み合わせることで地熱資源ポテンシャルの評価が可能になる。

2 m survey method and its improved device application in Dongshan geothermal field in Xiamen in China

Preliminary geothermal surveys to identify areas of potential geothermal anomalies are the most important stage in traditional hydrothermal-type geothermal resource exploration procedures. Temperature gradient wells are limited because of their accessibility issues and high costs, whereas the 2 m survey is considered a rapid, efficient, and inexpensive method to measure temperature accurately and allow for rapid vectoring toward geothermal anomalies in cases where thermal groundwater is not overlain by near-surface cold aquifers. An improved quick and portable measurement device is developed that adds in situ thermal conductivity tests based on temperature. The device, which is easy to assemble, portable, and suitable for two or three people in field work, had been calibrated by laboratory experiments. The device was applied in Dongshan geothermal field, Xiamen City in China, and 18 measurement positions were arranged. Results clearly described the geothermal anomalies in the area and revealed two temperature anomaly centers, namely a strong one in the eastern area and a weak one in the western area. Moreover, a speculated fault provided a hydraulic connection between the eastern and western areas. According to the 2 m survey, a steady-state heat conduction model has been used to inverse the 20 m temperature. The average temperature error of all boreholes in 20 m is 3 °C, whereas the relative errors between actual and forecast values are less than 10 %. Therefore, the 2 m survey method and improved device shows good performance in preliminary geothermal surveys.

Preliminary estimation of electrolytic hydrogen production potential from renewable energies in Ecuador

An initial assessment of the production potential of H2 by electrolysis is performed in Ecuador with electricity from renewable sources. The renewable energies considered are: solar photovoltaic, wind, geothermal and hydropower. The information about their potential is based on maps of solar and wind resources, geothermal surveys, as well as estimates on mini-hydro and spilled turbinable energy from hydroelectric plants with reservoir. The amount of H2 is obtained by considering a PEM electrolizer, with an efficiency of 75%, reaching a production of 4.55 × 108 kg/year in a likely scenario. Two different uses of H2 are presented: 1) automotive transportation, replacing gasoline and diesel and, 2) rural energy, replacing firewood for cooking in rural households in the country. As a result, H2 is able to replace 65% and 44% of the volumes of imported gasoline and diesel, respectively and the overall replacement of gasoline in 9 out of 23 provinces. Also, it is possible the total replacement of firewood in rural households in 20 provinces, and, under certain conditions, the H2 surplus could be used to completely cover the electricity needs in the same rural households in 20 provinces. It is concluded that, there are certain opportunities in Ecuador to include H2 in its energy matrix, contributing to improve the supply of secondary energy, raising the life quality in rural areas, mitigation of environmental pollution and strengthening the national economy. All this makes necessary to conduct more detailed technical and economic studies.

Application of Comprehensive Geophysical Prospecting Method to Geothermal Resource Exploration in Yiliang County, Kunming

The earth is a huge heat reservoir and contains amounts of heat. The geothermal internal heat is about50000 times more than the energy in the oil and gas resources. In order to investigate the occurrence and formation of geothermal resources in Yiliang basin, several methods, such as electrical sounding, Very low frequency electromagnetic method, and Electrostatic α-card method are applied in the exploration area. The geothermal resource survey of the Yiliang basin has been carried out. Based on the above results, two investigation wells have been designed at the location of favorable geological conditions in the exploration area. The application of multiple geophysical prospecting methods obtains preferable effort in geothermal exploration and provides meaningful reference for the area with lower level of the geothermal survey work.

Geothermal and bathymetric surveys of Brouton Bay (Uratman Volcano, Simushir I., Kuril Islands)

This paper presents results from a comprehensive analysis of geothermal and bathymetric surveys in the Brouton Bay on Simushir I. (Kuril Islands). High heat flow values through the bay bottom are typical of the present-day volcanoes at the Kuril island system. The results of the bathymetric survey were used to develop a digital map and a 3D model for the Bay basin and to detect an underwater volcanic dome. Comparison of geothermal and bathymetric data permitted delineation of the outer and inner ring faults that surround the atrio of Uratman Volcano. This evidence shows that the volcano is active at the present time.

Structure and activity of the geothermal field of Hvalfjörður (Iceland) from brittle tectonic, geothermal and paleostress analysis

AbstractThis paper presents the results of brittle tectonic, palaeostress inversion, and hydrothermal mineralisation studies of the Hvalfjörður low-temperature geothermal field in Southwest Iceland. This geothermal field (including two pronounced thermal anomalies) is located in the highly altered core area of an extinct and deeply eroded Tertiary central volcano. Most of the geothermal water appears to be conducted by vertical extension fractures. Palaeostress analysis indicates a rather complex stress history, with four major trends of extension involving normal and strike-slip faulting modes as well as dyke injection. Analysis of the data on the relative chronology indicates that these four regimes were closely intricate in time and space. The most important regime is a NW-SE, rift-perpendicular extension related to the oceanic rifting in Iceland. This trend partly controls the past (Pliocene-Early Pleistocene) hydrothermal activity in the Hvalfjörður area; however, an E-W rift-oblique extension also occurred with a N-S trending fracture system including normal faults, dykes and veins that show higher levels of hydrothermal mineralisation. Currently, there is strong hot-water convection, producing a thermal anomaly, in this N-S-trending fracture system. Our study highlights the paleostress evolution and the development of fracture systems in Hvalfjörður, including the past geothermal history; nevertheless the most efficient tool in geothermal prospection in such complex area remains the shallow geothermal survey. It has proved successful in many localities in Early Pleistocene to Miocene rocks where no surface indication of geothermal activity exists.

Geothermal area detection using Landsat ETM+ thermal infrared data and its mechanistic analysis—A case study in Tengchong, China

Thermal infrared (TIR) remote sensing is an important technique in the exploration of geothermal resources. In this study, a geothermal survey is conducted in Tengchong area of Yunnan province in China using TIR data from Landsat-7 Enhanced Thematic Mapper Plus (ETM+) sensor. Based on radiometric calibration, atmospheric correction and emissivity calculation, a simple but efficient single channel algorithm with acceptable precision is applied to retrieve the land surface temperature (LST) of study area. The LST anomalous areas with temperature about 4–10K higher than background area are discovered. Four geothermal areas are identified with the discussion of geothermal mechanism and the further analysis of regional geologic structure. The research reveals that the distribution of geothermal areas is consistent with the fault development in study area. Magmatism contributes abundant thermal source to study area and the faults provide thermal channels for heat transfer from interior earth to land surface and facilitate the present of geothermal anomalies. Finally, we conclude that TIR remote sensing is a cost-effective technique to detect LST anomalies. Combining TIR remote sensing with geological analysis and the understanding of geothermal mechanism is an accurate and efficient approach to geothermal area detection.

3D correlation imaging of the vertical gradient of gravity data

We present a new 3D correlation imaging approach for vertical gradient of gravity data for deriving a 3D equivalent mass distribution in the subsurface. In this approach, we divide the subsurface space into a 3D regular grid, and then at each grid node calculate a cross correlation between the vertical gradient of the observed gravity data and the theoretical gravity vertical gradient due to a point mass source. The resultant correlation coefficients are used to describe the equivalent mass distribution in a probability sense. We simulate a geological syncline model intruded by a dike and later broken by two vertical faults. The vertical gradient of gravity anomaly of the model is calculated and used to test the approach. The results demonstrate that the equivalent mass distribution derived by the approach reflects the basic geological structures of the model. We also test the approach on the transformed vertical gradient of real Bouguer gravity data from a geothermal survey area in Northern China. The thermal reservoirs are located in the lower portion of the sedimentary basin. From the resultant equivalent mass distribution, we produce the depth distribution of the bottom interface of the basin and predict possible hidden faults present in the basin.

“Uniform geothermal gradient” and heat flow in the Qiongdongnan and Pearl River Mouth Basins of the South China Sea

The Pearl River Mouth Basin (PRMB) and Qiongdongnan Basin (QDNB) are oil and gas bearing basins in the northern margin of the South China Sea (SCS). Geothermal survey is an important tool in petroleum exploration. A large data set comprised of 199 thermal conductivities, 40 radioactive heat productions, 543 measured geothermal gradient values, and 224 heat flow values has been obtained from the two basins. However, the measured geothermal gradient data originated from diverse depth range make spatial comparison a challenging task. Taking into account the variation of conductivity and heat production of rocks, we use a “uniform geothermal gradient” to characterize the geothermal gradient distribution of the PRMB and QDNB. Results show that, in the depth interval of 0–5 km, the “uniform geothermal gradient” in the PRMB varies from 17.8 °C/km to 50.2 °C/km, with an average of 32.1 ± 6.0 °C/km. In comparison, the QDNB has an average “uniform geothermal gradient” of 31.9 ± 5.6 °C/km and a range between 19.7 °C/km and 39.5 °C/km. Heat flows in the PRMB and QDNB are 71.3 ± 13.5 mW/m 2 and 72.9 ± 14.2 mW/m 2, respectively. The heat flow and geothermal gradient of the PRMB and QDNB tend to increase from the continental shelf to continental slope owing to the lithosphereic/crustal thinning in the Cenozoic.

Reservoir characteristics and development plan of the Oguni geothermal field, Kyushu, Japan

Geothermal power development at the Oguni field, central Kyushu, is planned to begin in the year 2001 with a double flash system generating 20 MW e. The Oguni reservoir has been delineated by systematic geothermal surveys, well tests and reservoir engineering studies. The fractured reservoir is horizontally layered and divided into northern and southern portions. Both of them have NaCl dominant fluids ranging from 200 to 240°C. The northern reservoir covers a large area including the Takenoyu Fault Zone and has a relatively high permeability (kh≈80–230 darcy-m). By contrast, the southern reservoir covers a relatively small area and has limited transmissivity. The southern reservoir has a higher pressure (1 MPa) than the northern reservoir, indicating little connectivity between them. Based on numerical calculations, as well as the surface topography and environmental aspects, the production and reinjection zones have been separated, and a large part of the necessary fluid will be produced from the northern reservoir along the Takenoyu Fault and a small part will be taken from the southern reservoir. The separated water will be reinjected into the northernmost part of the northern reservoir, in order to prevent a cold sweep problem for production.

Deep Tectonic Processes and Superaccumulation of Metals Related to Granitoids in the Nanling Metallogenic Province, China

The Nanling region is an important nonferrous and rare metal metallogenic province in South China, in which most of the deposits are related to granitoids in genesis. It covers southern Hunan, southern Jiangxi, Guangxi, Guangdong and Fujian provinces, with a total area of about 550,000 km2. This metallogenic province is well known in the world for its rich tungsten and tin resources. In the past 40-odd years, a vast amount of mineral exploration activities and studies of the geology of mineral deposits have been carried out and great achievements obtained in the province. This paper is focused on a discussion about the deep tectonic processes in the orogenic belt during the Mesozoic and their contribution to the superaccumulation of metals. Tectonically, this metallogenic province is composed of three units: (1) the marginal continental orogenic belt in the Southeastern Coast fold system in the Yanshanian; (2) the intercontinental orogenic belt in the collision suture belt between the Yangtze and Cathaysian plates mainly in the Caledonian; and (3) the intracontinental orogenic belt induced by subduction of the ocean crust and delimination of the mantle lithosphere in the Yanshanian. It is suggested that superaccumulation of metals in this metallogenic province was caused by the existence of mantle rooted tectonics at the depth based on comprehensive studies of geophysical information of seismic, geothermal and magnetotelluric surveys in Nanling and its adjacent areas. The Xihuashan wolframite quartz vein deposit, the Shizhuyuan W, Sn, Mo, Bi greisen-skarn deposit and the Dachang tin-polymetallic deposit are three typical examples of the deep tectonic processes. However, this kind of deep tectonic processes only act as the “engine” of the superaccumulation of metals, which means that they should have to correspond with the super-crust ore-controlling pattern of “lines-rows-clusters” (L-R-C). This recognization is expected to play an important role in assessment of mineral resources in this province.

Genesis of the plutonic-hydrothermal system around quaternary granite in the kakkonda geothermal system, Japan

The Kakkonda plutonic-hydrothermal system has as its heat source the Quaternary Kakkonda granite. The Kakkonda granite has a thick (∼1.3 km) contact-metamorphic zone, known mainly from the geothermal survey well WD-1a (total depth: 3729 m) drilled by the New Energy and Industrial Technology Development Organization (NEDO). The Kakkonda granite is a stock several tens of square kilometers in area with an upper contact about 1.5–3 km deep. It is a composite pluton varying from tonalite to granite. The early-stage granitic rocks are slightly metamorphosed to biotite grade by late-stage granitic rocks. K-Ar ages of separated minerals from the granitic rocks in both stages show the same cooling ages of 0.24–0.11 Ma for hornblende, 0.21–0.02 Ma for biotite, and 0.14–0.01 Ma for potassium feldspar. These are the youngest ages for granite in the world. The K-Ar ages become almost zero at ∼580°C for biotite and potassium feldspar, and at ∼350°C for illite. The Kakkonda granite intruded into a regional stress field in which the minimum principal stress was ENE–WSW and nearly horizontal. The regional stress field coincides with that of a previously recognized F2 fracture system before ∼0.4–0.3 Ma. Both stages of the Kakkonda granite and the contact aureole are fractured by recent tectonism, resulting in a zone of hydrothermal convection from about 2.5–3.1 km depth up to the surface. The boundary between the zone of hydrothermal convection and the underlying zone of heat conduction occurs ∼250–550 m below the upper contact of the Kakkonda granite, and has a temperature of ∼380–400°C.

Temperature logging to describe the movement of sewage-polluted surface water infiltrating into a fractured rock aquifer

In 1992–1993, temperature logs were used to study the movement of sewage-polluted surface water infiltrating into the fractured limestone of an experimental site located in the southeastern part of the Lez Basin (Southern France). The wells investigated were located on either side of a sewage-polluted stream and intersected water-bearing fractures characterised by large contrasts in hydraulic conductivity. From the results of temperature-depth profiles measured in four closely spaced wells of 60 m depth (W7, W8, W 10 and W 16) during the period February 1992–June 1993 and the findings of a previous and more extensive geothermal survey, we examined the spatial distribution and the temporal variability of ground-water temperature during periods influenced or not influenced by percolating sewage-polluted water. Results of this thermal survey, which were in good agreement with those of a physico-chemical and bacteriological survey simultaneously carried out at the site, provided a substantial amount of information on the distribution of contaminant flow pathways. Well W8, which showed high fluctuating ground-water temperature anomalies, intersected a solution-enlarged part of a bedding joint which seemed to carry much of the sewage-polluted infiltrating water. Ground water in this conductive opening also had a low physico-chemical and bacteriological ‘stability’ and the highest average contaminant concentrations. In contrast, Wells W10, W16 and, to a lesser extent, Well W7 displayed only low ground-water temperature anomalies during periods influenced by percolating sewage-polluted water. Ground water circulating through the thin and rather closed fissures intersected by these wells was less sensitive to pollution, as it had a greater thermal, physico-chemical and bacteriological ‘stability’ and the lowest average. contaminant concentrations. Thus, we suggest that in advance of more focused monitoring programmes, temperature-depth profiles in wells could effectively be used to described the effect of the structural features of fractures limestone aquifers on the movement of infiltrating contaminants.

GEMS: Geothermal Expert Modeling System

In carrying out geothermal-energy development projects, an exhaustive study has to be conducted on the local subsurface geothermal system based on extensive geothermal surveys and well data. The New Energy and Industrial Development Organization has had an extensive geothermal research program under way since 1987, known as the “Nationwide Geothermal Resources Exploration Project.” In this program, the total analysis system, which is called the “Geothermal Expert Modelling System (GEMS),” has been developed to systematize all processes of building models of geothermal systems based on the various regional exploration data. The aim of the system is to select narrow promising areas (about 50–60 square kilometers) for more elaborate exploration from within a region extending over hundreds of square kilometers, by analyzing the various explorations, and by building a geothermal system model of the area. This scheme includes studies to consolidate individual geothermal survey data into an integrated data base and to work out a computer-aided support system for building geothermal models. It calls for the integration of these processes into a system on a user-friendly, engineering work-station that has sufficient graphic functions. An attempt was made to actually identify promising areas in regions covered by wide-area surveys on hydrothermal systems, using the proposed total analysis system.