Heat Flow Values Research Articles

Deep thermal state on the southern margin of the Zhangzhou Basin based on the electrical conductivity model

Exploring the internal spatial and thermal structure of the Zhangzhou Basin is of great scientific significance in understanding the properties of the deep heat sources and the heating mechanism of hot springs in this region. This study estimates the temperature distribution within the upper mantle of the Basin's southern margin using the Arrhenius equation and Hashin-Shtrikman bounds based on a two-dimensional crust-mantle electrical resistivity model. We also employ a layered simulation technique to calculate the crustal temperature distribution using a one-dimensional steady-state heat conduction equation, constrained by the upper mantle's top and ground surface temperatures. This approach displays the characteristics of the longitudinal variations and horizontal inhomogeneities in crust-mantle temperature. Additionally, we estimate the heat flow values within the study area. Our findings reveal that: (i) the upper mantle (at depths of 30 - 50 km) exhibits a temperature range of 700 - 1100 °C, with the presence of local Moho and upper mantle uplifts; (ii) the crustal temperature spans from 21 - 900 °C, with a diminishing influence of the upper mantle uplift area on crustal temperature at shallower depths; (iii) the surface heat flow values derived from our simulations range between 87 and 100 mW/m2, averaging at 93.23 mW/m2; (iv) the exploration of dry heat rock in this region is likely to reach a depth of at least 6 km. These results suggest that the genesis of hot springs in the study area is not solely influenced by the heat energy extracted from large-area granitic surrounding rocks during a long transport process, but is also considerably affected by local deep thermal anomalous bodies and deep-large faults.

Heat Flow in the Northeastern Continental Margin of Russia

Abstract —This work is set out to summarize, analyze and revisit results of the geothermal studies carried out in Northeast Russia. A catalog of measured heat flow values has been compiled, and on its basis a map of the region’s heat flow distribution has been constructed. Geodynamic activity of the tectonic structures in Northeast Russia, their thermal regime in which the heat flow is a critical indicator, is largely determined by the interaction between the Eurasian and North American lithospheric plates and smaller-order plates located in the northeastern part of the Asian continent. The areas of interaction between the Eurasian and North American lithospheric plates are marked by the Arctic-Asian seismic belt, which is characterized by intense orogenesis, modern volcanism, active seismicity, diverse geothermal regimes, and large heterogeneity of measured heat flow values. On the Chukotka Peninsula, the helium isotope method was used to estimate heat flow values. It is proposed to consider the class of geodynamic activity of tectonic structures as one of the factors of the geothermal regime.

Evaluation of source rocks and prediction of oil and gas resources distribution in Baiyun Sag, Pearl River Mouth Basin, China

By conducting organic geochemical analysis of the samples taken from the drilled wells in Baiyun Sag of Pearl River Mouth Basin, China, the development characteristics of hydrocarbon source rocks in the sag are clarified. Reconstruct the current geothermal field of the sag and restore the tectonic-thermal evolution process to predict the type, scale, and distribution of resources in Baiyun Sag through thermal pressure simulation experiments and numerical simulation. The Baiyun Sag is characterized by the development of Paleogene shallow lacustrine source rocks, which are deposited in a slightly oxidizing environment. The source rocks are mainly composed of terrestrial higher plants, with algae making a certain contribution, and are oil and gas source rocks. Current geothermal field of the sag was reconstructed, in which the range of geothermal gradients is (3.5–5.2) °C/100 m, showing an overall increasing trend from northwest to southeast, with significant differences in geothermal gradients across different sub-sags. Baiyun Sag has undergone two distinct periods of extensional process, the Eocene and Miocene, since the Cenozoic era. These two periods of heating and warming events have been identified, accelerating the maturation and evolution of source rocks. The main body of ancient basal heat flow value reached its highest at 13.82 Ma. The basin modelling results show that the maturity of source rocks is significantly higher in Baiyun main sub-sag than that in other sub-sags. The Eocene Wenchang Formation is currently in the stage of high maturity to over maturity, while the Eocene Enping Formation has reached the stage of maturity to high maturity. The rock thermal simulation experiment shows that the shallow lacustrine mudstone of the Wenchang Formation has a good potential of generating gas from kerogen cracking with high gas yield and long period of gas window. Shallow lacustrine mudstone of the Enping Formation has a good ability to generate light oil, and has ability to generate kerogen cracking gas in the late stage. The gas yield of shallow lacustrine mudstone of the Enping Formation is less than that of shallow lacustrine mudstone of the Wenchang Formation and the delta coal-bearing mudstone of the Enping Formation. The numerical simulation results indicate that the source rocks of Baiyun main sub-sag generate hydrocarbons earlier and have significantly higher hydrocarbon generation intensity than other sub-sags, with an average of about 1 200×104 t/km2. Oil and gas resources were mainly distributed in Baiyun main sub-sag and the main source rocks are distributed in the 3rd and 4th members of Wenchang Formation. Four favorable zones are selected for the division and evaluation of migration and aggregation units: No. ▪ Panyu 30 nose-shaped structural belt, No. ▪ Liuhua 29 nose-shaped uplift belt and Liwan 3 nose-shaped uplift belt, No. ▪ gentle slope belt of Baiyun east sag, and No. ▪ Baiyun 1 low-uplift.

The Effect of CO on the Exothermic Characteristics of Low-Temperature Oxidation in Coal

ABSTRACT In recent years, abnormally high concentrations of CO gas have often been detected in goaf areas of coal mines in China, which have posed a serious threat to safe production in coal mines and the life and safety of underground personnel. The effect of CO on the exothermic characteristics of low-temperature oxidation in coal was studied by analyzing the exothermic characteristics, heat release, oxidation stages, and activation energy of coal at different CO concentrations using a C600 microcalorimeter. The experimental results indicated that CO promoted the coal oxidation at low temperature, but inhibited it after reaching 144°C. When the CO concentration is 30%, the exothermic characteristics of coal in low-temperature oxidation adsorption stage were significantly affected, with the heat flow value decreased by 27.0% and the initial exothermic temperature point moved forward by 3.9 K. In the later stage of the oxidation reaction, the heat release of coal was linearly negatively correlated with CO concentration. The higher the concentration, the lower the heat release. These findings contribute to understanding the combustion mechanism of coal in high-concentration CO atmosphere and provide valuable insights for designing and optimizing coal utilization technologies.

An updated terrestrial heat flow data set for the Junggar basin, northwest China: implications for geothermal resources

SUMMARY Terrestrial heat flow plays a vital role in determining the present thermal regimes of sedimentary basins, offering a robust foundation for understanding hydrocarbon maturation processes and the geothermal resource potential. The Junggar basin is one of the largest and most petroliferous superimposed petroleum basins in China. However, research on heat flow is scarce. In this study, 94 new high-quality heat flow values are derived from through borehole temperature analysis and thermal conductivity measurements of rocks. The results indicate that (1) the geothermal gradient in the basin varies from 11.4 to 28.3 °C km−1, with a mean value of 20.9 ± 3.4 °C km−1, and the heat flow varies from 23.4 to 64.5 mW m−2, with a mean value of 45.1 ± 8.4 mW m−2. The overall low geothermal gradient and heat flow are attributed to the continuous cooling during the Meso-Cenozoic. (2) At basin scale, the high heat flow values are primarily concentrated in areas characterized by basement uplift, whereas the low heat flow values are mainly located in the depressions. This suggests that thermal refraction is the primary factor influencing the heat flow variations. (3) Although large-scale development and utilization of geothermal resources face challenges, certain local areas in the basin show promise for geothermal resource utilization.

Assessment of heat flow in the northern part of the Indigiro– Zyryansky trough (Yakutia)

An approximate estimation of the heat flow value was performed for three deep parametric wells drilled in the northern part of the Indigiro-Zyryansky trough. Boreholes have uncovered Paleogene and Upper Jurassic rocks. Geothermal gradients were calculated from the temperature values at the lower boundary of the cryolithozone (0 ºC) and at the downhole. The thermal conductivity of rocks was roughly estimated from published data. The calculated heat flow on the Indigirskaya area is on average 70 mW/m2 . The values of heat flow values were recorded in the previously studied neighboring areas. Thus, the heat flow estimate obtained by the authors in the Indigiro-Zyryansky trough correspond fully to the available data on the heat flow level in this region of East Yakutia.

Resurgent dome and super-hot enhanced geothermal system: The Sahinkalesi Massif within the Hasandag Stratovolcanic Province, Central Anatolia, Turkey

The Sahinkalesi, a volcanic dome located NNE of Hasandağ, Türkiye exhibits anomalous heat flow value, geothermal gradient and the Curie point depth is located at very shallow depth in this region. Our investigation indicates presence of super-critical thermal regime (378°C) at about 4 km depth and the MT analysis indicate shallow magma chamber at about 5 km depth. The crust is relatively thin below this region with the low-velocity region located at depth of about 36 km. Thermo-Hydro-mechanical model investigation has been carried out using finite element discretization technique. For faulted zone reservoir models, 30 years of geothermal energy exploitation does not cause thermal breakthrough for mass flow rates up to 500 kg/s, however, the mean stress developed in the reservoir becomes much larger and may be unsustainable for the reservoir stability. To ensure the success of a fractured reservoir model, the use of multiple wellbores is recommended. In the case of a closed-loop geothermal system, the primary concern is the control of thermoelastic stress. This can be achieved either by increasing the wellbore depth while reducing the injection mass flow rate, or by extending the wellbore's horizontal component. The outlet temperature in both the cases maintained at 275°C. This is the first time a superhot EGS site has been identified in Türkiye.

Estimating spatio-temporal variable parameters of Epidemic Type Aftershock Sequence model in a region with limited seismic network coverage: a case study of the East African Rift System

SUMMARY The Epidemic-Type Aftershock Sequence (ETAS) model is currently the most powerful statistical seismicity model that reproduces the general characteristics of earthquake clustering in space and time. However, its application can be hampered by biased parameter estimations related to earthquake catalogue deficiencies, particularly in regions where the spatial coverage of local recording networks is relatively poor. Here, we systematically investigate the possible influences of the effect introduced by data truncation through the choice of the cut-off magnitude (${{m}_{\rm cut}})$ and missing events due to heterogeneity of the seismic network on ETAS parameter estimates along the East African Rift System (EARS). After dividing the region into six source zones based on rheological and mechanical behaviours, the ETAS model is fitted to the earthquakes within each zone using the Davidon–Fletcher–Powell optimization algorithm. The fits and variations in parameter estimates are compared for each zone to the others and the seismological implications are discussed. We found that some parameters vary as a function of ${{m}_{\rm cut}}$ primarily driven by changes in catalogue size. Additionally, a systematic regional dependency of ETAS parameters is found across source zones. Furthermore, a median heat flow value for each analysed source zone in the EARS is calculated. In contrast to previous findings in other tectonic settings, the results reveal no significant correlations between the crustal heat flows and the ETAS parameters describing earthquake productivity (${{K}_0}$) and the relative efficiency of an earthquake with magnitude M to produce aftershocks ($\alpha $). Our findings have significant implications for understanding the mechanisms of earthquake interaction and, therefore, provide tight constraints on the model's parameters that may serve as a testbed for existing earthquake forecasting models in this region where the vulnerability of local buildings and structures exacerbate seismic risk.

Lithospheric resistivity structure of the Xuefeng Orogenic Belt and its implications for intracontinental deformation in South China

The Xuefeng Orogenic Belt (XFOB), located in the central part of the South China Block, is a typical Mesozoic intracontinental orogen in the central Jiangnan Orogenic Belt. By collecting magnetotelluric (MT) data across the XFOB, we obtained the resistivity structure of the lithosphere, which sheds light on the Mesozoic intracontinental orogenic processes in the XFOB. The resistivity structure reveals a low-resistivity body (<10 Ω∙m), beneath the XFOB, dipping southeast wards from a depth of 10 km to the bottom of the crust. This conductor is interpreted as a relic of the lower detachment zone, which coincides with low-density areas obtained from joint inversion of seismic models. It is believed to result from mineral fluids migrating along the thrust fault and squeezing sulfides into folds. Four low-resistivity bodies were identified at three extensional locations along the Jiangshan-Shaoxing Fault and at the Cili-Baojing Fault. The low-resistivity body (<10 Ω∙m) at the junction of the Shaoyang and the Hengyang Basin is located at the point where the Moho depth thins. The variation trend of the terrestrial heat flow values, with this low-resistivity body as the plate boundary, is consistent with the average variation of the terrestrial heat flow values within the block. We propose that the low-resistivity body under the Qidong-Yongzhou-Guilin fault conforms to the characteristics of the suture zone in the resistivity structure. Its existence indicates that the missing location of the Jiangshan-Shaoxing suture zone of the Yangtze and Cathaysia Block in the middle-southwest section of the South China Block is the Qidong-Yongzhou-Guilin fault. The Yangtze Block and the Hengyang Basin show high resistivity, the depth of which reaches 100 km and 40 km, respectively. Based on the resistivity model and geological data, the XFOB experienced Triassic compression, leading to basement decollement, thrusting, and nappe structures due to low-angle Paleo-Pacific Plate subduction. This compression also led to the uplift of the orogenic belt. Moreover, under the tension caused by the high-angle retreat of the Paleo-Pacific Plate, the Cretaceous extensional tectonics led to detachment along the thrust faults, forming half-graben and basin structures along the margins.

Optimisation Design of Thermal Test System for Metal Fibre Surface Combustion Structure

The metal fibre surface combustion structure has the characteristics of strong thermal matching ability, short response time, and strong shape adaptability. It has more advantages in the thermal test of complex hypersonic vehicle surface inlet, leading edge, etc. In this paper, a method of aerodynamic thermal simulation test based on metal fibre surface combustion is proposed. The aim of the study was to create a uniform target heat flow on the inner wall surface of a cylindrical specimen by matching the gas jet flow rate and the geometry of the combustion surface. The research adopted the optimisation design method based on the surrogate model to establish the numerical calculation model of a metal fibre combustion jet heating cylinder specimen. One hundred sample points were obtained through Latin hypercube sampling, and a database of design parameters and heat flux was established through numerical simulation. The kriging surrogate model and the non-dominated sequencing genetic optimisation algorithm with elite strategy were adopted. A bi-objective optimisation design was carried out with the optimisation objective of the coincidence between the predicted and the target heat flux on the inner wall of the specimen. The results showed that the average relative errors of heat flow density on the specimen surface were 8.8% and 6% through the leave-one-out cross-validation strategy and the validation of six test sample points, respectively. The relative error values in most regions were within 5%, which indicates that the established kriging surrogate model has high prediction accuracy. Under the optimal solution conditions, the numerical calculation results of the heat flow on the inner wall of the specimen were in good agreement with the target heat flow values, with an average relative error of less than 5% and a maximum value of less than 8%. These results show that the optimisation design method based on the kriging surrogate model can effectively match the thermal test parameters of metal fibre combustion structures.

Three-stages tectonic evolution controls the differential distribution of hydrocarbons in the West Java backarc basin

The West Java Basin is a typical back-arc basin in Southeast Asia and one of Indonesia's main petroleum provinces. In the past ten years, it has been found that the new hydrocarbon reserves are on the rise, and a amount of resources to be discovered is significant. The distribution of hydrocarbon resources and the tectonic evolution characteristics of the basin are systematically explored, and the differences in hydrocarbon distribution and its main controlling factors in the back-arc basin of West Java are analyzed. The uneven distribution pattern of hydrocarbon is mainly controlled by the differential distribution of source rocks in the subsidence period. The distribution of the main source rocks is influenced by the "three-stage" tectonic development process that governs the distribution of sedimentary facies in various sedimentary environments throughout the tectonic subsidence period. Second, the weakening of the crust and magmatism facilitates the production of high heat flow values in the shallow strata of the back-arc area, thereby accelerating the pyrolysis and hydrocarbon generation of source rocks. The study delineates the formation and distribution of various types of oil and gas across various blocks. Prospective basin exploration sites include the shallow-deep water zones in the basin's south-central sector, as well as underexplored terrestrial regions. The exploration history and hydrocarbon resources identified within the West Java back-arc basin support these findings.

Opening and Post-Rift Evolution of Alpine Tethys Passive Margins: Insights from 1D Numerical Modeling of the Jurassic Mikulov Formation in the Vienna Basin Region, Austria

This study employed 1D numerical pseudo models to examine the Upper Jurassic carbonate succession, focusing on the Mikulov Formation in the Vienna Basin region. It addresses the protracted and complex history of the Jurassic source rock play, revealing a transition from rapid syn-rift (&gt;200 m/Ma) to slower post-rift sedimentation/subsidence of the overlying layers during extensional deformation (up to 120 m/Ma with a thickness of 1300 m). This provides valuable insights into the rift-to-drift stage of the central Alpine Tethys margin. The Mikulov marls exhibit characteristics of a post-rift passive margin with slow sedimentation rates. However, a crustal stretching analysis using syn-rift heat flow sensitivity suggested that thermal extension of the basement alone cannot fully explain the mid-Jurassic syn-rift stage in this segment of the Alpine Tethys. The sensitivity analysis showed that the mid-late Jurassic differential syn-rift sequences were exposed to slightly cooler temperatures than the crustal stretching model predicted. Heat flow values below 120 mW/m2 aligned with measurements from deeply settled Mesozoic successions, suggesting cold but short gravity-driven subsidence. This may account for the relatively low thermal maturation of the primary source rock interval identified by the time-chart analysis, despite the complex tectonic history and considerable sedimentary burial. The post-Mesozoic changes in the compaction trend are possibly linked to the compressional thrusting of the Alpine foreland and postdating listric faulting across the Vienna Basin.

Analysis of Transient Current and Heat Flow during Voltage Holds: For Relaxed and Unrelaxed G/NMC811 Cells

This study investigates the transient heat flow during voltage holds for multi-layer pouch G/NMC811 lithium-ion cells. When applying a voltage hold to estimate the amount of parasitic side reactions, there is first a transient phase followed by a steady state. According to the literature, reversible processes mainly influence the transient phase, while the steady state presents the side reaction current. This work investigates the contributions to the transient behavior, evaluating the thermal and electrical signals and deconvoluting the different parasitic side reactions. In addition, a comparison between relaxed and unrelaxed states is performed, analyzing different temperatures and voltages. The results show that the relaxed graphite cells quickly reached a constant parasitic heat flow value with minimal transient effects. In contrast, the unrelaxed cells presented increased transient effects in the parasitic heat flow signal that can last more than 300 h. The electric transient originates mainly from anode overhang effects and SEI regrowth, while the thermal transient consists predominantly of SEI regrowth. Overall, the thermal signals stabilize faster than the electrical signals, giving calorimetry an advantage for faster estimation of parasitic side reactions.

Geotermalny przepływ ciepła w Portugalii kontynentalnej

Heat flow density measurements in Portugal were made in boreholes used for mining prospecting. Heat flow density values in the sedimentary basins of the western and southern margins of the country were obtained using data from oil or gas prospecting works. Due to the scarcity of data in the central and northern regions of the country, numerical models based on some characteristics of the region were used to obtain more heat flow values. The total of heat flow values used in this work is 69, with 17 values obtained using numerical models, 36 obtained in boreholes and 16 obtained from oil/gas prospecting wells data. The analysis and location of these data allows to define different regions in the territory and characterize them using average values of heat flow density, temperature gradient and thermal conductivity. Statistical values with all the data in the territory are also presented.

Applying machine learning to characterize and extrapolate the relationship between seismic structure and surface heat flow

SUMMARY Geothermal heat flow beneath the Greenland and Antarctic ice sheets is an important boundary condition for ice sheet dynamics, but is rarely measured directly and therefore is inferred indirectly from proxies (e.g. seismic structure, magnetic Curie depth, surface topography). We seek to improve the understanding of the relationship between heat flow and one such proxy—seismic structure—and determine how well heat flow data can be predicted from the structure (the characterization problem). We also seek to quantify the extent to which this relationship can be extrapolated from one continent to another (the transportability problem). To address these problems, we use direct heat flow observations and new seismic structural information in the contiguous United States and Europe, and construct three Machine Learning models of the relationship with different levels of complexity (Linear Regression, Decision Tree and Random Forest). We compare these models in terms of their interpretability, the predicted heat flow accuracy within a continent and the accuracy of the extrapolation between Europe and the United States. The Random Forest and Decision Tree models are the most accurate within a continent, while the Linear Regression and Decision Tree models are the most accurate upon extrapolation between continents. The Decision Tree model uniquely illuminates the regional variations of the relationship between heat flow and seismic structure. From the Decision Tree model, uppermost mantle shear wave speed, crustal shear wave speed and Moho depth together explain more than half of the observed heat flow variations in both the United States [$r^2 \approx 0.6$ (coefficient of determination), $\mathrm{RMSE} \approx 8\, {\rm mW}\,{\rm m}^{-2}$ (Root Mean Squared Error)] and Europe ($r^2 \approx 0.5, \mathrm{RMSE} \approx 13\, {\rm mW}\,{\rm m}^{-2}$), such that uppermost mantle shear wave speed is the most important. Extrapolating the U.S.-trained models to Europe reasonably predicts the geographical distribution of heat flow [$\rho = 0.48$ (correlation coefficient)], but not the absolute amplitude of the variations ($r^2 = 0.17$), similarly from Europe to the United States ($\rho = 0.66, r^2 = 0.24$). The deterioration of accuracy upon extrapolation is caused by differences between the continents in how seismic structure is imaged, the heat flow data and intrinsic crustal radiogenic heat production. Our methods have the potential to improve the reliability and resolution of heat flow inferences across Antarctica and the validation and cross-validation procedures we present can be applied to heat flow proxies other than seismic structure, which may help resolve inconsistencies between existing subglacial heat flow values inferred using different proxies.

Geothermal resource evaluation of the Middle Permian Qixia-Maokou Formation in the southern Sichuan Basin, China

The southern Sichuan Basin is an abnormal area of high present geothermal fields in the Sichuan Basin. It is a favorable area for the development of geothermal resources in the Sichuan Basin. But its evaluation of geothermal resources is lagging, which has severely affected the development of geothermal resources in the southern Sichuan Basin. In the paper, firstly, based on the temperature data of wells, the geothermal gradients and heat flows of typical wells in the study area were calculated, and the temperatures at the top and bottom of the reservoir in the Qixia-Maokou Formation were calculated using a one-dimensional steady-state heat conduction equation. Then, geothermal resource intensities and reserves of the Middle Permian Qixia-Maokou Formation in the southern Sichuan Basin were evaluated by using a method for rapidly calculating geothermal resources in sedimentary basins by multi-data fusion. Finally, suggestions for geothermal development were proposed. The results show that the geothermal gradient and heat flow values in the southern Sichuan Basin range from 15.6 to 33.70 °C/km and 49 to 85 mW/m2, respectively, and the temperature of the reservoir in the Qixia-Maokou Formation ranges from 50 to 120 °C. The geothermal resources are 3.09 × 1021 J, equivalent to 105 billion tons of standard coal, and the recoverable resources are 6.18 × 1020 J, equivalent to 21 billion tons of standard coal. The development of demonstration projects will focus on the mid- to low-temperature geothermal power generation, geothermal grain drying and geothermal agriculture in the southwestern region of the southern Sichuan Basin. The research results can provide a resource basis for the development of geothermal resources in the southern Sichuan Basin.

Thermal evolution of deeply buried lower Paleozoic strata and its influence on hydrocarbon accumulation in the Tarim Basin, Northwest China

The Ordovician carbonate reservoirs in the Tarim Basin are hotspots for oil and gas exploration in recent years. However, due to the lack of effective paleo-geothermometers in carbonate formations, thermal history studies have been greatly restricted. In this study, we reconstructed thermal history of Ordovician carbonate intervals in Tarim Basin by applying clumped isotopes, equivalent vitrinite reflectance ( Requ) and zircon (U–Th)/He ages as thermal indicators. The modeled results indicated that there are three phases of heat flow evolution in the Shuntuoguole low-uplift. (a) The gradual cooling stage during Ordovician-carboniferous. The heat flow is gradually decreasing during this period. (b) Rapidly raised stage in the early Permian period. The heat flow in Shunbei and Shuntuo area are raised rapidly during this period and the maximum is 51–65 mW/m2, but the SN3 well in Shunnan area increased slightly and the heat flow values of other single wells were still relatively stable. (c) The decline stage since Middle Permian. The tectonic activity is relatively stable and the geothermal heat flow is gradually reduced during this period, but the heat flow in Shunnan area is higher than the Shunbei and Shuntuo areas. Due to the control of thermal evolution, the dissolution of the Ordovician carbonate reservoir in Shuntuoguole area occurred earlier than the formation of large quantities of hydrocarbon materials, and the improvement of reservoir physical properties provided sufficient conditions for the late oil and gas filling, which was conducive to the preservation of large oil and gas reservoirs.

Thermo-kinetics study of microalgal biomass in oxidative torrefaction followed by machine learning regression and classification approaches

Solid biofuels derived from microalgae represent a low-cost, high-volume bioproduct opportunity with excellent CO2 biofixation capability, contributing significantly to the attainment of net zero. Oxidative torrefaction also offers a more economical pretreatment to upgrade its solid fuel properties. This study investigates the thermo-kinetics aspect of oxidative torrefaction of microalgae with varying O2 concentrations using thermogravimetric and differential thermal analysis (TGA-DTA). Isoconversional kinetic modeling is applied to mass-loss data and shows average activation energies of 172.57, 174.68, 199.42, and 209.03 kJ‧mol−1 at 0, 3, 12, and 21 % O2 concentrations, respectively. The effect of O2, especially at 12 vol%, significantly reduces the calculated activation energy at lower conversion. DTA also reveals lower heat flow values under oxidative than inert torrefaction. Thermo-kinetics data are then utilized to conduct machine learning approaches. Regression via artificial neural networks shows that the prediction of conversion and heat flow values are predominantly dictated by the temperature, followed by heating rate and O2 concentration. Finally, classification using the k-nearest neighbors algorithm highlights the effects of factors at specific ranges of conversion and heat flow responses. The O2 concentration is significant only at early conversion (X<0.1) and contributes to generally lower heat flow values.

Curie point depth, thermal gradient and heat flow along the Ethiopia Rift System and adjacent plateaus using spectral evaluation approach: implications for geothermal resources

The Ethiopia Rift System (ERS) is a section of the East African Rift System within Ethiopia extending from the Afar in the northeast to the Kenya border in the southwest. It is apparent that magmatism and magmatic intrusions influence the crustal shape in the ERS resulting in its thinning and the shallowing of magmatic sources at various locations within it. As a consequence, more than 31 volcanoes hosting hydrothermal structures with a conceivable potential to generate massive quantities of geothermal energy have been identified along the ERS. In this study, we map the Curie Point Depth (CDP) over the ERS based on the analysis of aeromagnetic data extracted from the World Digital Magnetic Anomaly Map. Spectral evaluation method was used to estimate the boundaries (top and bottom) of the magnetized crust. Reduced-to-pole (RTP) aeromagnetic records have been divided into 105 (50% overlap) square blocks of 200 × 200 km size. The Curie temperature (580 °C) of magnetite was used to determine the thermal gradient and the heat drift in the area. The depths obtained for the bottom of the magnetized crust are assumed to correspond to the Curie Depths, where the magnetic layer loses all its magnetization. The determined values of Curie Point Depth, geothermal gradient and heat flow for the 50% overlapped 105 blocks, respectively, range from 8.85 to 55.85 km, 10.38 to 65.54 °C/km and 25.96 to 163.84 mW/m2. Lower CPD (< 20 km) in the ERS was obtained between Mille and Gewane (southwest Afar), between Adama (Nazret) and Yerer (NMER) and between Wendo Genet and Koti (SMER) localities. These areas, showing low CPD, exhibit excessive geothermal gradient and high heat flow all of which indicate the presence of significant geothermal potential.

Differences and Causal Mechanisms in the Lithospheric Thermal Structures in the Cratons in East China: Implications for Their Geothermal Resource Potential

The thermal structure of the lithosphere is key to understanding its thickness, properties, evolution, and geothermal resources. Cratons are known for their low heat flow and deep lithospheric roots. However, present-day cratons in East China have geothermal characteristics that are highly complex, with variable heat flow values, diverging from the typical thermal state of cratons. In this study, we conducted a detailed analysis of the geothermal geological background of the cratons in East China, summarizing the thermal state and tectono-thermal processes of different tectonic units, calculating the temperature at various depths, and discussing differences in temperature and thermal reservoirs at different depths. The observed lithospheric thermal thickness within the North Jiangsu Basin and the Bohai Bay Basin is notably reduced in comparison to that of the Jianghan Basin and the Southern North China Basin. The phenomenon of craton destruction during the Late Mesozoic emerges as a pivotal determinant, enhancing the geothermal resource prospects of both the Bohai Bay Basin and the North Jiangsu Basin. Our findings contribute significantly to the augmentation of theoretical frameworks concerning the origins of heat sources in global cratons. Furthermore, they offer invaluable insights for the methodical exploration, evaluation, advancement, and exploitation of geothermal resources.