Geothermal Anomalies Research Articles

Main Controlling Factors and Formation Mode of Geothermal Anomaly in Eastern Chenghe Mining Area of Weibei Coalfield

Geothermal anomaly has gradually become a prominent issue affecting the efficient mining of coal with the depth of coal mining increasing in eastern Chenghe mining area of Weibei coalfield. Here, we comprehensively investigated the distribution characteristics of the present geothermal field, analyzed the main controlling factors, and constructed forming mode of geothermal anomaly by the temperature measurement in surface borehole and underground water, combined with coal-rock thermal conductivity test. The results show that the geothermal gradient ranged from 25.7°C/km to 54.3°C/km. The areas with geothermal gradient greater than 30°C/km accounted for 88.31%, and there was the highest gradient value in the southeast F1 fault zone. The heat flow was between 66.81 mW/m2 to 128.49 mW/m2, which belonged to the obvious high heat flow area. Under the action of the main controlling factors such as fault, fold, coal-rock thermal conductivity, and groundwater activity in the region, the geothermal gradient and geothermal heat flow values showed an increasing trend from northwest to southeast. According to the distribution characteristics of heat flow and the action mechanism of main controlling factors, the geothermal anomaly in the study area was finally divided into two forming modes, i.e., fault-deep circulating hot water uplifting type and coal seam heat resistance-fold type. The research provides guidance for the geothermal hazard prevention of coal mine and the rational development and utilization of geothermal resources.

Hydrochemical Characteristics of Hot Springs in the Intersection of the Red River Fault Zone and the Xiaojiang Fault Zone, Southwest Tibet Plateau

The coupling relationship between regional seismic activity and the hydrogeochemical field provides an important theoretical basis for regional earthquake precursor exploration. The intersection area of the Red River fault zone (RRF) and the Xiaojiang fault zone (XJF) in southeast Yunnan province has become the focus area of earthquake monitoring and prediction because of its special tectonic position in China. There were 20 hot springs that were sampled and analyzed in the laboratory for major elements, including trace elements, silica, stable isotopes (δ18O and δD), and strontium isotopes, from the years 2015 to 2019. (1) The meteoric water is the main source of recharge for thermal springs in the study area, and recharged elevations ranged from 1.1 to 2 km; (2) the geothermometer method was used to estimate the region of thermal storage temperature, and its temperature ranged between 64.3 to 162.7 °C, whereas the circulation depth ranged from 1.1 to 7.2 km. Hydrochemical types were mainly controlled by aquifer lithology, in which sodium bicarbonate and sulphuric acid water gathered mainly in the RRF, while calcium bicarbonate water gathered mainly in the XJF. According to the silicon–enthalpy equation method, the temperature range and cold water mixing ratio were 97–268 °C and 61–97%, respectively; (3) the circulation depth of the RRF was deeper than that of the XJF, and it was mainly concentrated in the second segment and the fourth segment on the RRF. Most of the hot spring water was immature with a weak water–rock reaction; (4) the hot water intersections of RRF and XJF were obviously controlled by the fault and the cutting depth of granite; (5) the relationship discussed between geothermal anomaly and earthquake activity had a good correspondence with regional seismicity. The intensity of the reaction between underground hot water and the surrounding rock may lead to the change of pore pressure, and the weakening effect of groundwater on fracture may change accordingly, followed by the change in the adjustment of tectonic stress. Eventually, the difference in seismic activity was shown, implying that deep fluid has an important control action on the regional seismicity.

Experimental application of bottom temperature measurements in lakes of Bolshoy Solovetsky Island to test the geothermal anomaly hypothesis

The article reports the results of an experiment to assess the geothermal potential of the territory based on measurements of water reservoirs’ bottom temperatures.The research was conducted in 2021 on Bolshoy Solovetsky Island, which, according to some data, is characterized by the presence of geothermal anomaly on the one hand, and has a large number of lakes on the other. For lakes with depths greater than 5 m, the results of temperature measurements indicate that the temperature profiles correspond to the dimictic type of lakes – with two periods of circulation in spring and autumn. During the experiment, abnormal values of bottom temperatures at depths of more than 15 m were detected in Lakes Bolshoe Krasnoe and Shchuchye: 5.16–5.26 °C for Lake Shchuchye, and 6.16–6.56 °C for Lake Bolshoe Krasnoe. The possible causes of these anomalies are discussed including: chemical reactions in the near-bottom sediment layer, increased heat flow in the upper part of the Earth’s crust, and wind mixing in the lakes. Recommendations are given for further study of the anomalies in order to clarify their nature.

Detection of geothermal anomalies in the Northern Lake Abaya geothermal field, Main Ethiopian Rift

The detection of geothermal anomalies using Thermal Infrared (TIR) remote sensing data is challenging because of how sensor specifications (such as the infrared wavelength used for the measurement, spectral dependence of the emissivity, angle at which the measurement is made, state of the surface and height of the sensor above the surface) and physical parameters (such as solar radiation, topography, albedo, soil compaction and coherence of rocks) affect Land Surface Temperature (LST) retrieval and analysis. This work tests whether TIR remote sensing measurements with thorough spatial and temporal sampling can improve LST retrievals. Multi-temporal TIR data from 2000 through 2019 from Landsat 7 and 8 TIR instruments and the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) were used to detect geothermal areas in the geologically active region of the southern Main Ethiopian Rift. In addition, field-based temperature data from 19 sites were evaluated for comparison to the remotely detected geothermal anomaly areas. We have used the single-channel algorithm and Normalized Difference Vegetation Index (NDVI) method of emissivity retrieval to derive LST for each year. The result shows that the mean LST is highest in 2003 (320.1 K) and lowest in 2019 (303.1 K). The change in mean LST was between −9 K to 13 K. These LST results from ASTER images were validated with MODIS LST products and showed a correlation coefficient >0.6. LST of the year 2003 has been much closer to the actual temperature value from field data. Fifteen sites (79%) fit with the identified geothermal anomaly areas. LST values in known geothermal activity sites show no correlation (< 0.5) with time attesting. That is, even though LST varies with time (e.g., day and night and seasonal changes), the LST of areas with geothermal potential remain more or less constant on yearly basis.

Mapping the spatial distribution of fossil geothermal manifestations and assessment of geothermal potential of the Tangyin rift, Southeast of Taihang Mountain in China

The spatial prediction of geothermal sites along the southeast side of Taihang Mountain in the Tangyin rift is a critical goal in the development of renewable energy resources in cities such as Hebi in Henan province, which has significant potential for geothermal energy production due to the existence of deep faults and Cenozoic volcano. The study aimed to delineate areas with high geothermal manifestations for detailed geothermal exploration and well-test drilling. To define favorable zones for geothermal potentiality, multi-source datasets were chosen to generate evidence thematic layers that demonstrate the distribution of geothermal anomalies such as geologic maps, structural maps, Land Surface Temperature maps (LST), and hydrothermal mineral alterations maps. The remote sensing and Geographical Information System (GIS) approaches were integrated to map fossil geothermal manifestations and appraise the promising geothermal zones from Landsat 8 OLI/TIRS and Advanced Spaceborne Thermal Emission and Reflection Radiometer-Digital Elevation Model (ASTER-DEM) dataset using the Analytic Hierarchy Process (AHP), which is one of the Mult-criteria Decision Making methods. Results show LST values ranging from 22.6°C to 45.4°C, with the highest values found along the faults and volcanic areas. The hydrothermal alteration minerals discriminated from band ratios of 4/2, 6/5, and 6/7 for iron oxide, ferrous minerals, and clays reveal the presence of high amount of montmorillonite and illite minerals along the faults and volcanoes which are related to hot fluid circulation from subsurface. Structural analysis shows that the major structural trend follows the NNE Tangdong and Tangxi faults, with high density on the west side of the Tangxi fault where there is good exposure of outcrop but less fault density on the east side due to sedimentation in a low land which may conceal geological structures. Lastly, all the thematic layers of geothermal factors were reclassified, ranked, and integrated by the weight overlay logic model based on the influence of geothermal suitability to map potential areas for geothermal resources whereby 5 zones were obtained ranging from very poor to very good. The promising potential sites are mostly found along the highly deep structures of the major Tangxi fault crosscutting the permeable lithology of carbonate rocks and around the Hebi volcanoes. The distribution of hot springs and geothermal wells of the Hebi field were correlated and verified against the potential geothermal anomalies map. The overall integrated method proposes an advanced technique for designing the Tangyin rift’s exploration plan and development actions for geothermal resources utilization, which can be used for exploration of any unveiling geothermal potential sites.

Prospective Evaluation of Geothermal Resources in the Shangqiu Uplift of the Southern North China Basin with Magnetotelluric Detection

The magnetotelluric sounding (MT) method is used to detect and study the deep stratigraphic structure and hidden faults in the Shangqiu Uplift. A total of 4 MT profiles are arranged, and 97 stations are collected. The nonlinear conjugate gradient (NLCG) two-dimensional inversion method is used to jointly invert data from both the TE and TM modes after a dimensionality analysis and impedance tensor decomposition; reliable two-dimensional resistivity models are produced since the data quality is excellent. Three-dimensional inversion is carried out to full impedance tensor as well to produce a three-dimensional resistivity model of the study area, which shows good consistency with the two-dimensional models. The results show that the electrical structure of the Shangqiu Uplift has typical layered characteristics, which can be divided into three layers from top to bottom, namely low-, medium-to-high-, and high-resistivity layers. According to the resistivity models and in combination with the gravity, aeromagnetic, seismic, and regional geological data of the study area, a geological map of the basement rock of the Shangqiu Uplift is produced. Two prospective geothermal anomaly areas are proposed according to the distribution of the high-resistivity anomaly formed by the basement uplift, which has a good corresponding relationship with the high-value area of the regional geothermal field. A geothermal exploration well (SR-1) is constructed in one of the inferred prospective geothermal anomaly areas. The well is 1702 m deep, with a water output of 1500 m3/day and a wellhead water temperature of 51.5 °C. This is the geothermal well with the largest water yield in the Shangqiu area at present, which provides a new basis for future geothermal exploration, development, and utilization.

Genetic Mechanism of Geothermal Anomaly in the Gaoyang Uplift of the Jizhong Depression

The Gaoyang uplift is rich in geothermal resources, but there are few studies on the regional geothermal genetic mechanism. A large number of geothermal wells fail in position calculation because of a shortage of basis. By using the methods of P-wave velocity structure imaging and magnetotelluric sounding, it draws the following conclusions: 1) The crustal thickness in the Gaoyang uplift area is relatively thin, about 32 km; 2) The cutting depth of the Gaoyang East fault exceeds 28 km and has reached the bottom of the lower crust. It is a large tensile fault that provides a channel for mantle heat flow into the shallow crust; 3) The Gaoyang uplift and its surrounding depressions form a concave-convex base fluctuation mode, which is conducive to the accumulation of heat flow to the uplift; 4) The deep carbonate thermal reservoir in the Gaoyang uplift is overlaid with Cenozoic sand and mudstone strata, with a thickness of more than 3000 m and low thermal conductivity, which is conducive to the preservation of thermal storage heat. Therefore, the shortening of the heat conduction path caused by regional crustal thinning, convective heat conduction of large faults, concave-convex structure, and thick Cenozoic caprock are the reasons why the heat reservoir temperature in the Gaoyang uplift is higher than that around, which provides a theoretical basis for geothermal development and utilization.

The genesis of Rare-alkali metal enrichment in the geothermal anomalies controlled by faults and magma along the northern Yadong-Gulu rift

Geothermal water from the hot springs in the Yadong-Gulu rift (YGR) of southern Tibet is extremely enriched in rare-alkali metal (RAM) elements; however, the mechanism of enrichment has long been debated. Much attention has been given to the deep melting magma of the YGR, but no direct evidence indicates whether and how it is connected to the RAM anomaly of hot springs. Determining the mechanism of RAM enrichment and its variations with the time and space of hot springs will contribute to the exploration of the hydrothermal metallogenic systems. This paper presents numerical hydrothermal numerical circulation models constrained by the geological data and the geophysical structure of the YGR. The results illustrate that the depths of boundary faults control the anomalous temperatures of hot springs. High-temperature springs (such as Yangbajing) could be induced by deep faults extending to the middle crust, whereas magma at a depth greater than 10 km has a limited effect on geothermal anomalies. Secondary faults define the extent of hydrothermal circulation and further determine the distribution of thermal anomalies across the rift. We simulate the enrichment and distribution of RAMs from a deep magma source. The pathways of RAMs from the source are consistent with hydrothermal circulation. RAM concentrations are lower in infiltrating groundwater and higher in ascending hot water. In general, deep faults control the hydrothermal circulation of geothermal groundwater. Deep faults and magma further constrain the distribution of RAM anomalies.

Geothermal Mechanism and Reservoir Characterization with Multiscale Analysis of the Potential Field and MT Profile in the Yanqing-Huailai Basin, North China

Abstract Geothermal energy has attracted increasing attention worldwide due to its abundant reserves, stability, and sustainability. Based on the survey of geothermal resources in the Yanqing-Huailai Basin, this paper conducts comprehensive data study, demonstrates geothermal distribution and multiscale characteristics, and constructs the geothermal mechanism and conceptual model to promote regional geothermal energy development and utilization. Our study proposes to characterize geothermal reservoirs using geophysical data ranging from the representative geothermal field scale to the basin scale. Hydrochemical samples were also collected. According to the results of multiscale analysis and interpretation, combined with field geological and geothermal investigations, it is concluded that the Dahaituo pluton is composed of acid granite and monzonite granite, with low gravity and high magnetic anomaly. Its intrusion and development are responsible for the local geothermal anomaly. Multiscale analysis and source depth estimation of potential field data and MT profile interpretation were carried out. The regional thermal structure and reservoir characteristics were demonstrated from the deep to the shallow. In addition, according to the regional geological background and geophysical interpretation, a three-dimensional geological model is constructed to characterize the distribution law and genetic mechanism of geothermal anomalies. The study shows that strong Cenozoic tectonic movement and the intrusion and development of rock mass are the main factors causing local geothermal anomaly. The development of regional deep and major faults and extensional structures, as well as the channels and space formed by the breaking of rocks at the intersection of faults, provides advantageous conditions for the upwelling, migration, and convergence of geothermal fluids. The recharge of surface water in the intermountain basin and thermal convection drive the circulation of the geothermal system.

Differential elemental stoichiometry of two Mediterranean evergreen woody plants over a geochemically heterogeneous area

Leaf nutrient composition and stoichiometry reflect complex interactions of the plant with its environment and are useful traits to explore ecological processes and relationships. In the present study, the foliar elemental compositions of two common Mediterranean woody species, the evergreen broad-leaved Quercus ilex and the coniferous Pinus pinaster growing in an area of Central Italy known for geochemical and geothermal anomalies, were investigated. To assess the site-specific and age-dependent pattern of foliar composition and stoichiometry, macronutrients (C, N, P, K, Mg, S) and trace elements (Al, As, Ba, Cd, Cr, Cu, Fe, Hg, Ni, Pb, Sb, V, Zn) were determined in leaves and needles of three different ages (6-, 12- and 24-month-old) collected from metalliferous (geothermal, mining) and rural areas. Leaves of Q. ilex showed comparatively high concentrations of micronutrients (i.e., Cu, Fe and Zn), while needles of P. pinaster accumulated significantly high concentrations of potentially toxic elements (i.e., As, Pb and S). No significant trend was found in elemental concentrations in relation to the age of leaves and needles. Multi-element stoichiometry of P. pinaster was driven by the geochemical heterogeneity of the sites, suggesting plastic adaptation at the sites with the most selective edaphoclimatic conditions (i.e., patches with nutrient poor and metalliferous soils). On the other hand, the content of both nutrients and potentially toxic elements in Q. ilex leaves varied little across the study area, reflecting stoichiometric stability; this is consistent with the ecophysiological features of Q. ilex as a late-successional species with a dominant role in the ecosystems of the Mediterranean area. Our findings demonstrate the value of foliar stoichiometric traits for understanding plant adaptation in a heterogeneous environment and also the consequences of biotic interactions during succession.

Heat flow and 2D multichannel seismic reflection survey of the Devil's Hole geothermal reservoir in the Wagner basin, northern Gulf of California

The Wagner basin, located in the northernmost Gulf of California, hosts a large reservoir with geothermal potential documented in recent heat flow surveys. Although there is evidence of heat generation above the average value for an oceanic crust in the Wagner basin, it is unclear what the heat source is. To better understand the thermal structure in the northern Gulf of California, we acquired four 2D multichannel seismic reflection profiles and two systematic heat flow profiles across the Wagner basin. The survey targeted a geothermal anomaly, which we denominated “Devil's Hole” in a clear reference to pockmarks on the seafloor, and very high heat flow values. The heat flow profiles are ∼12 and ∼9 km long, are sub perpendicular to each other, have a nominal measurement spacing of ∼1 km, and were located along the transects of two of the four seismic reflection profiles. The two remaining seismic profiles are ∼34 and ∼40 km long, respectively, and are oriented SWW-NEE. To obtain seismic images, we used a conventional seismic processing workflow. After heat flow data correction, the minimum, maximum, and standard deviation of heat flow values for the Wagner basin are 295±42 and 10,894±114 mW/m2. We interpret the relatively high heat flow and large variability in the central part of the acquired profiles is caused by upward fluid flow at the Wagner fault zone. In contrast, the lower heat flow in the western flank of the basin suggest conductive heat transfer given the absence of faults. Based on these observations, we develop a geological model in which venting is not the product of a nascent spreading center as other authors have suggested. Instead, hydrothermal activity appears to result from isolated thermal plumes, rising from the base of the sedimentary column, captured by permeable fracture systems.

Fluid geochemistry and geothermal anomaly along the Yushu-Ganzi-Xianshuihe fault system, eastern Tibetan Plateau: Implications for regional seismic activity

Hydrothermal activity and seismicity are abundant along the Yushu-Ganzi-Xianshuihe fault system (YGXFS) in the eastern Tibetan Plateau. However, the processes and factors that control hydrothermal fluid circulation at a regional scale remain less constrained, and the relationship between geothermal anomaly and seismic activity is poorly known. In this study, we report an integrated dataset of thermal water chemistry (δ18OH2O, δDH2O, and δ13C of dissolved inorganic carbon (DIC)) to identify the origin, circulation path, and reservoir properties of hydrothermal fluids and then reveal the relationship between fluid circulation and seismic activity. The thermal waters are mainly classified as Na-HCO3 type with minor Ca-Na-HCO3 and Na-HCO3-Cl types. The δ18OH2O (−18.7‰ to −14.5‰) and δDH2O (−142‰ to −110‰) values indicate recharge of meteoric waters, which infiltrated along the YGXFS to 2–6 km depths and underwent mixing with deep fluids prior to their discharge at the surface. A mass balance model based on δ13CDIC values (−4.3‰ to 5.9‰) and DIC contents of thermal waters reveals the involvement of CO2-bearing fluids from mantle and thermo-metamorphic decarbonation of crustal marine limestones in tectonic CO2 outgassing from the active fault. The estimated reservoir temperatures (85–336 °C) based on silica geothermometer of the thermal waters decrease from southeast to northwest along the YGXFS. Notably, the epicenters of strong earthquakes (Ms ≥ 6) are mostly located in the transition zone of geothermal anomalies according to spatial distribution of the reservoir temperatures. Combined with geological and geophysical information, we suggest that the heterogeneity of crustal thermal structure and the upwelling of deep fluids may play an essential role in the distribution of thermal springs and the high frequency of earthquakes along the YGXFS.

Magmatic evolution and architecture of an arc-related, rhyolitic caldera complex: The late Pleistocene to Holocene Cerro Blanco volcanic complex, southern Puna, Argentina

Abstract Through the lens of bulk-rock and matrix glass geochemistry, we investigated the magmatic evolution and pre-eruptive architecture of the siliceous magma complex beneath the Cerro Blanco volcanic complex, a Crater Lake–type caldera complex in the southern Puna Plateau of the Central Andes of Argentina. The Cerro Blanco volcanic complex has been the site of two caldera-forming eruptions with volcanic explosivity index (VEI) 6+ that emplaced the ca. 54 ka Campo Piedra Pomez ignimbrite and the ca. 4.2 ka Cerro Blanco ignimbrite. As such, it is the most productive recent explosive volcano in the Central Andes. The most recent eruptions (younger than 4.2 ka) are dominantly postcaldera effusions of crystal-rich domes and associated small explosive pulses. Previous work has demonstrated that andesitic recharge of and mixing with rhyolitic magma occurred at the base of the magma complex, at ~10 km depth. New isotopic data (Sr, Nd, Pb, and O) confirm that the Cerro Blanco volcanic complex rhyolite suite is part of a regional southern Puna, arc-related ignimbrite group. The suite defines a tight group of consanguineous siliceous magmas that serves as a model for the evolution of arc-related, caldera-forming silicic magma systems in the region and elsewhere. These data indicate that the rhyolites originated through limited assimilation of and mixing with upper-crustal lithologies by regional basaltic andesite parent materials, followed by extensive fractional crystallization. Least squares models of major elements in tandem with Rayleigh fractionation models for trace elements reveal that the internal variations among the rhyolites through time can be derived by extensive fractionation of a quartz–two feldspar (granitic minimum) assemblage with limited assimilation. The rare earth element character of local volumes of melt in some samples of the Campo Piedra Pomez ignimbrite basal fallout requires significant fractionation of amphibole. The distinctive major- and trace-element characteristics of bulk rock and matrix of the Campo Piedra Pomez and Cerro Blanco tephras provide useful geochemical fingerprints to facilitate regional tephrochronology. Available data indicate that rhyolites from other neighborhood centers, such as Cueros de Purulla, share bulk chemical characteristics with the Campo Piedra Pomez ignimbrite rhyolites, but they appear to be isotopically distinct. Pre-eruptive storage and final equilibration of the rhyolitic melts were estimated from matrix glass compositions projected onto the haplogranitic system (quartz-albite-orthoclase-H2O) and using rhyolite-MELTS models. These revealed equilibration pressures between 360 and 60 MPa (~10–2 km depth) with lowest pressures in the Holocene eruptions. Model temperatures for the suite ranged from 695 to 790 °C. Integrated together, our results reveal that the Cerro Blanco volcanic complex is a steady-state (low-magmatic-flux), arc-related complex, standing in contrast to the flare-up (high-magmatic-flux) supervolcanoes that dominate the Neogene volcanic stratigraphy. The silicic magmas of the Cerro Blanco volcanic complex were derived more directly from mafic and intermediate precursors through extensive fractional crystallization, albeit with some mixing and assimilation of local basement. Geochemical models and pressure-temperature estimates indicate that significant volumes of remnant cumulates of felsic and intermediate composition should dominate the polybaric magma complex beneath the Cerro Blanco volcanic complex, which gradually shallowed through time. Evolution to the most silicic compositions and final equilibration of some of the postcaldera domes occurred during ascent and decompression at depths less than 2 km. Our work connotes an incrementally accumulated (over at least 54 k.y.), upper-crustal pluton beneath the Cerro Blanco volcanic complex between 2 and 10 km depth. The composition of this pluton is predicted to be dominantly granitic, with deeper parts being granodioritic to tonalitic. The progressive solidification and eventual contraction of the magma complex may account for the decades of deflation that has characterized Cerro Blanco. The presently active geothermal anomaly and hydrothermal springs indicate the Cerro Blanco volcanic complex remains potentially active.

Joint interpretation technology of favorable HDR geothermal resource exploration in Northern Songliao Basin

Hot dry rock (HDR) is considered a new clean and renewable energy source. China is rich in HDR resources, but viable and reliable resource evaluation techniques and exploration methods have not been available yet. This research method, consisting of deep exploration combined with shallow drilling, screens the geothermal anomaly regions using heavy magnetic, electric measurement, seismic and thermal joint interpretation technology, and verifies the geophysical multiplicity with massive oilfield drilling data to locate the favorable HDR target region. The research results show a regionally geothermal abnormal area. We use relative impedance combined with seismic profile to recognize the HDR target region. The geophysical exploration and geological joint interpretation technology are faster and more accurate than the single geophysical exploration technology. The comprehensive analysis believes that the high resistance granite body in the southern Paleo-central uplift zone, with its area 500km2, its thickness 150–330m, its static formation temperature reaching 152° in the depth of 3360m, its high rock thermal conductivity, its good deep fracture, and base fracture development, is a fragmented granite and weathered shell, easy for artificial reservoir re-constructing. There is high preciseness in locating the favorable target region for HDR development.

Geothermal anomalies on the eastern flank of the Cherokee basin, southeastern Kansas, USA

Bottomhole temperature measurements from oil and gas drilling in southeastern Kansas on the eastern flank of the Cherokee basin, in combination with a suite of about 2,200 differential temperature logs recently obtained from wireline logging in coalbed methane wells, define several higher-temperature anomalies at the top of the Mississippian Subsystem strata. Temperatures slightly in excess of 90 oF (35 oC) at depths of about 900 ft (275 m) correspond to geothermal gradients as high as about 60 oC/km.&#x0D; Sparse historical measurements of heat flow in the cratonic Cherokee basin indicate that the thermal anomalies are not likely caused by locally high heat flow. Heat flow in the Cherokee basin is probably in line with most other shallow cratonic basins. The higher-temperature thermal anomalies defined by logging temperatures do not correspond to previously mapped faults or other structural features in the Phanerozoic sedimentary section, but some anomalies are underlain by Precambrian basement lineations that are detectable with aeromagnetic and gravity measurements. Well-log determination of shale content in the Pennsylvanian sedimentary strata overlying the Mississippian limestones indicates that low thermal conductivity caused by higher shale content may cause some of the thermal anomalies. &#x0D; Lateral (advective) movement of warmer, highly saline water from the basin axis cannot account for the anomalies because the anomalies are not characterized by exceptionally highly saline water in Mississippian strata. Similarly, recorded static fluid levels of wells disposing of oilfield saltwater into the Mississippian strata and the deeper Cambrian-Ordovician Arbuckle Group indicate that the deeper Arbuckle strata generally do not have sufficient formation pressure to force Arbuckle formation water upward into the Mississippian through either natural fractures or leaky wellbores. Small-scale changes in salinity, in combination with geologic structuring indicating faulting, make a case for vertical (convective) movement of heated, less saline water from the Arbuckle Group into overlying Mississippian limestones in isolated localities. Buoyancy of the Arbuckle formation water (due to temperature and salinity differences with the cooler and more saline Mississippian water) could also be the primary force behind the convection. Convergence of cooler freshwater moving westward off the Ozark dome and more saline basinal water moving eastward also could be a factor in defining the limits of some thermal anomalies.

GEOTHERMAL FIELD OF BELARUSIAN PART OF PODLASKA-BREST DEPRESSION

The article presents an information on geothermal conditions of the platform cover within the Podlaska-Brest Depression, parameters characterizing the thermal field of the region. Geothermal maps of temperature and heat flow distribution were compiled based of thermograms registered in boreholes. Geothermal anomalies of temperature and heat flow distribution within the region and its adjacent geological structures are identified. They largely depend on the features of the geological structure of the crustal blocks. The variability of the thermal field within the territory of the zone of active water exchange (the fresh water zone) is considered. It is shown that the geothermal field of the region is characterized by its nonuniformity. Anomalies of low values of temperature and heat flow were identified in the adjacent parts of the Belarussian Anteclise and Polesie Saddle. Both the temperature and heat flow significantly increase in the Belarusian part of the Podlaska-Brest Depression. The maximum values of geothermal parameters were noted in parts of the depression adjacent to the Belarusian-Polish border. A decrease of the heat flow is observed in the direction of the Lukóv-Ratno Horst. An estimate of the density of geothermal resources for the strata of Cambrian deposits has been carried out. The density of recoverable resources in this stratum of the region varies in a wide range: from 0 (at the eastern boundary of the depression, when they pinch out) to more than 350 kg o. e/m2. The maximum values are observed northwest of Brest in the area adjacent to the Belarus-Poland border, in particular, within the well-studied geothermal Pribug Structure. They represent the interest for practical use.

Application of Infrared Remote Sensing and Magnetotelluric Technology in Geothermal Resource Exploration: A Case Study of the Wuerhe Area, Xinjiang

As a new green energy source, geothermal resource’s exploration, development, and utilization are an important direction in geophysical exploration at present. In this study, the actual land surface temperature was inferred based on the thermal infrared band of Landsat8 remote-sensing images, and the information about the surface anomalies and their spatial distribution was obtained through a multifactor analysis. In addition, three magnetotelluric sounding profiles were deployed in the study area, and the geo-electric sections in the study area were obtained through inversion of the measured data. Then, based on the inverse geo-electric information and the land surface temperature anomaly information, we analyzed and verified the geothermal resource genesis of the thermal anomaly area and inferred the favorable geothermal resource area in the study area. The results show that these two methods can be used to compare and analyze the possible distribution of the geothermal resources in the study area in two dimensions: the spatial distribution on the surface and the vertical distribution in the subsurface. Moreover, the results of the geothermal anomalies inferred from the thermal infrared remote sensing and the geo-electric results inferred from the magnetotelluric data are in good agreement. This study demonstrates that the integrated application of thermal infrared remote sensing and magnetotelluric technology is a promising tool for geothermal exploration.

Gas origin linked to paleo BSR

The Central-South Chile margin is an excellent site to address the changes in the gas hydrate system since the last deglaciation associated with tectonic uplift and great earthquakes. However, the dynamic of the gas hydrate/free gas system along south central Chile is currently not well understood. From geophysical data and modeling analyses, we evaluate gas hydrate/free gas concentrations along a seismic line, derive geothermal gradients, and model past positions of the Bottom Simulating Reflector (BSR; until 13,000 years BP). The results reveal high hydrate/free gas concentrations and local geothermal gradient anomalies related to fluid migration through faults linked to seafloor mud volcanoes. The BSR-derived geothermal gradient, the base of free gas layers, BSR distribution and models of the paleo-BSR form a basis to evaluate the origin of the gas. If paleo-BSR coincides with the base of the free gas, the gas presence can be related to the gas hydrate dissociation due to climate change and geological evolution. Only if the base of free gas reflector is deeper than the paleo-BSR, a deeper gas supply can be invoked.

Thermal-mechanical modelling of rock response and damage evolution during excavation in prestressed geothermal deposits

Rock damage induced by underground excavation would cause irreversible degradation in the hydro-mechanical performance of the engineering rock mass depending on the excavation method, in-situ stress, and change of ambient conditions. As exploitation of resources continues being operated at hostile depths of the Earth's lithosphere, adaptive excavation design thus becomes imperative for ensuring sustainable mining development in the increasingly challenging environment. In this study, a new thermal-mechanical framework is developed to characterize the successive blast loading, transient unloading, and air-cooling sequence for dynamic excavation in prestressed geothermal deposits. To capture the complex rock behavior across vastly different timescales, a new diagnostic tool is proposed for identifying the exact source, nature, and range of excavation damage based on the stress projection technique. By scrutinizing the rock response throughout the excavation process via loading path evolution, novel insights are obtained in this study into the underlying mechanism and relative contribution of each sub-loading process in damage generation under different geopressure, geothermal, and excavation conditions. Our calculations demonstrate quantitatively that the release of in-situ stress and air-cooling of the working environment constitute the predominant causal mechanisms of rock damage for major deep excavation projects. Furthermore, our analysis has shown explicitly that the perturbation to the redistributed stress field by tunnel ventilation could stimulate rock creeping and thus give rise to stability concern for excavations buried in highly stressed deposits of intense geothermal anomalies. The findings of our study could refine the understanding of the complex excavation response and thus contribute to improved adaptive design for excavation work in hostile geological environments.

Geothermal Distribution Characteristics in the Qinshui Basin and Its Significance to the Production of Coalbed Methane.

Temperature significantly affects the storage and transport of coalbed methane (CBM). Studies of geothermal distribution characteristics are important for the exploration and exploitation of CBM. In this study, more than 150 heat flow temperature data from coalbed methane wells in the Qinshui Basin were analyzed to investigate the geothermal distribution and its controlling factors. The results show that the geothermal gradient of the no. 3 coal seam ranges from 0 to 3.7 °C/hm with an average of 1.6 °C/hm, and the terrestrial heat flow of the no. 3 coal reservoir ranges from 0.9 to 94.6 mW/m2 with an average of 41.5 mW/m2. The reservoir temperature shows high values in the central and northwest parts of the basin, while the east and west edges of the basin show negative geothermal anomalies. It is found that groundwater has significant effects on the geothermal distribution in the Qinshui Basin, and with the increase of the groundwater level, the geothermal gradient decreases linearly. In addition, the geothermal gradient and terrestrial heat flow first increase and then tend to be stable with the increase in value of the total dissolved substances. Besides, with an increase in floor elevation, the geothermal gradient first increases linearly and then decreases linearly, obtaining a maximum value at about 450 m (transition floor elevation). This phenomenon is the result of the balance between heat supplying and heat losing. The geothermal distribution characteristics in the Qinshui Basin determine the reservoir temperature of the coalbed methane, and in turn, the reservoir temperature affects the adsorption, desorption, and diffusion behaviors of coalbed methane in situ.