High Heat Flow Values Research Articles

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.

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.

Study on effective elastic thickness of lithosphere and its tectonic significance in surrounding area of Ordos Block

Based on EIGEN6C4 gravity field model data and ETOPO1 topographic data, we adopt the correlation analysis method based on Fan wavelet to calculate and analyze the distribution characteristics of effective elastic thickness (Te) and load ratio (F) of lithosphere in surrounding of Ordos block. On this basis, the relationship between the lithosphere Te and geological structure, seismic distribution, terrestrial heat flow and crustal deformation is analyzed. The results show that the lithosphere Te in the surrounding area of the Ordos block is obviously different among the tectonic blocks. The lithosphere Te value is low in the south of Qinling orogenic belt and the east of Fen-Wei graben basin. The maximum lithosphere Te value is distributed in the northwest and northeast margin of Ordos block. The lithosphere Te value is negatively correlated with the load ratio F. Earthquakes mainly occur in areas with low lithosphere Te value. Small lithosphere Te value indicates low strength of lithosphere. In such areas, the ability to resist crustal deformation is weak, and it is easy to generate stress accumulation and breed earthquakes. The area with high terrestrial heat flow value corresponds to low lithosphere Te value, showing a negative correlation. However, this negative correlation does not exist in the northwest margin of Ordos Block and Alashan border area, and the eastern margin of Ordos Lvliangshan area. Haiyuan-Liupanshan area has strong tectonic activity, frequent earthquakes and low lithosphere Te value. The internal strain accumulation of Ordos block is small, and the lithosphere Te value is high. The strain rate of the northern Shanxi fault depression zone is large, but the lithosphere Te value is also large, it is speculated that the terrestrial heat flow is the main factor affecting the lithosphere Te value.

Identification of active faults and tectonic features through heat flow distribution in the Nankai Trough, Japan, based on high-resolution velocity-estimated bottom-simulating reflector depths

Estimates of heat flow can contribute to our understanding of geological structures in plate convergent zones that produce great earthquakes. We applied automated velocity analysis to obtain the accurate seismic profiles needed for precise heat flow estimates using six new seismic profiles acquired during R/V Kaimei KM18-10 voyage in 2018. We calculated heat flow values in the accretionary wedge of the Nankai Trough off the Kii Peninsula, Japan, from the positions of widespread bottom-simulating reflectors (BSRs) in seismic reflection profiles. Calculated conductive heat flow values from the depth of the BSR agree with previous studies where a regional trend is observed from ~ 50 mW/m2 to < 40 mW/m2 60 km landward from the deformation front. This trend is caused by thickening of accretionary sediments and the subduction of the Philippines Sea plate. Segments of profiles are marked by anomalous high heat flow values. Such anomalies represent alterations of the shallow crustal thermal structure caused either by a combination of topographic affects, surface erosion of the seafloor, or by fluid flow that transports heat by advection. We interpret heat flow anomalies (~ 100 mW/m2) as indicators of active faulting, which correspond to low seismic velocity zones along faults. Our results also showed relatively high heat flow at the landward end of several survey lines close to the Kii Peninsula, which we interpret to the possible presence of plutonic rocks that underlie the Kii Peninsula and extend offshore and may be the cause of geothermal springs, steep geothermal gradients, and high heat flow.Graphical abstract

Lithospheric Structure of the Circum‐Pannonian Region Imaged by S‐To‐P Receiver Functions

AbstractThe lithosphere‐asthenosphere boundary and mid‐lithospheric discontinuities are primary attributes of the upper mantle. The Pannonian region is an extensional sedimentary basin enclosed by collisional orogens. Here, we estimate the negative phase depth of S‐to‐P receiver functions to image the lithospheric thickness and other discontinuities with high resolution, based on the recent dense seismological broadband networks. The lithosphere‐asthenosphere boundary is relatively shallow (&lt;90 km) in the Pannonian Basin system, and deeper (∼90–140 km) in the surrounding orogens, where average surface heat flow values are higher (120 mW/m2) and lower (50–70 mW/m2), respectively. The 1D and 2D common conversion point migration with 3D velocity model provide comparable but different resolution images beneath the wider region of the Pannonian Basin. We obtained deeper values in the Western (∼120 km) and Southern‐Carpathians orogens (∼135 km). Furthermore, we provide new information on the lithospheric thickness and its seismic properties in the eastern part of the study region (e.g., Apuseni Mountains (∼95 km), Eastern‐Carpathians (∼120 km), Moesian Platform (∼90 km) and Transylvanian Basin (∼85 km). The shallower negative phase depth can be interpreted as the lithosphere‐asthenosphere boundary beneath the Pannonian Basin system in agreement with its high heat flow values. In contrast, the deeper negative phase depth estimates in the colder surroundings can be interpreted as intra‐ or mid‐lithospheric discontinuities, when compared with local seismic tomography models. In this region, the correlation with heat flow implies that the observed negative phase depth is of thermo‐chemical or rheological nature.

The Correlation of Geothermal Energy Potential Deduced from Aeromagnetic and Aeroradiometric Data of Akiri and Environs, North-Central Nigeria

The aeromagnetic and aeroradiometric data were combined to investigate the geothermal energy potential of Akiri and Environs, North-Central Nigeria. The aeromagnetic and aeroradiometric data were obtained from the Nigerian Geological Survey Agency (NGSA), Abuja. The data consists of nine square map sheets of Wamba, Kwolla, Shendam, Lafia, Akiri, Ibi, Makurdi, Akwana and Wukari. The LANDSAT imagery data of the study area was obtained from the National Centre for Remote Sensing, Jos. The spectral analysis method was applied to aeromagnetic data to obtain the geothermal parameters of the magnetic sources. The results show that the depth-to-top of magnetic sources in the study area ranges between 0.76 and 4.46 km; while the depth-to-centroid ranges between 7.29 and 19.6 km. The depth-to-bottom of magnetic sources corresponds to the Curie point depth (CPD) in the study area which is the depth at which magnetic rocks lose their magnetism. The results show that the CPD varies between 12.70 and 37.22 km, the geothermal gradient varies between 15.58 and 45.67 ◦C/km, and the geothermal heat flow varies between 38.9 and 114.17 mW/m2. Two dimensional structural models were constructed to show the estimated depths at each profile taken. The models show uplifted crust and mantle in some areas due to magmatic intrusions which gave rise to low CPDs (12 to 28 km) which resulted to high geothermal heat flow values (60 to 115 mW/m2). The results show that there are low values of CPD in some areas which indicates that the study area has geothermal energy potential. The study shows that the geothermal energy potential deduced from aeromagnetic data correlates well with the geothermal energy potential deduced from aeroradiometric data.

DENSITY OF HYDROCARBONS AND DEEP HEAT FLOW OF THE TERRITORY (SOUTHEAST OF WESTERN SIBERIA)

Link for citation: Krutenko D.S., Isaev V.I., Isaev S.G. Density of hydrocarbons and deep heat flow of the territory (southeast of Western Siberia). Bulletin of the Tomsk Polytechnic University. Geo Аssets Engineering, 2023, vol. 334, no. 7, рр. 148-163. In Rus. The relevance. According to the ruling theory for organic origin of petroleum, geothermal regime is considered to be the main factor, which is responsible for realization of potential for oil generation. Therefore, it is not irrelevant to develop geothermics as a method of exploration geophysics for forecasting and evaluating oil and gas potential. Forecast tasks are reduced to detection local geothermal anomalies and establishing its relation to hydrocarbon deposits. This method may make a good showing while supplementary exploration in the territories with well-developed infrastructure and a large amount of wells as it is based on modelling and analysing of available data and does not propose additional field works. The main aim: establishing qualitative and quantitative relations between deep heat flow and oil and gas potential, also between gradient zones of heat flow and localization of hydrocarbon fields in the west of Tomsk Region. Objects: thermal field and oil and gas potential in the west of Tomsk Region. Subjects. The thermal field is described with such parameters as deep heat flow density and horizontal gradient of heat flow. Hydrocarbon fields are divided depending on fluid type into oil, oil-gas-condensate and gas-condensate. Methods. The deep heat flow was determined through paleotemperature modelling. The grid with cells of 20×20 km was set on study territory in increments of 10 km. Heat flow values were determined in the centers of each cell using Kriging interpolation method. The absolute horizontal gradient of heat flow was calculated on the same grid using five spot formula. Quantitative parameter of oil and gas potential – hydrocarbon density – was determined on the same grid. Quantitative relations were investigated by correlation and regression analysis. Relationships of heat flow density and horizontal gradient of heat flow with localization of hydrocarbon fields of different fluid type were detected by one-way ANOVA test. Results. The main results of this study are established distribution patterns for deposits of different fluid type in thermal field. Correlation analysis showed highly significant correlation coefficients. The conclusion. Oil and oil-gas-condensate fields tend to the average heat flow values (52 mW/m2), while gas-condensate are associated with high heat flow values (57 mW/m2). The value of the absolute horizontal gradient of heat flow increases in row oil fields – oil-gas-condensate fields – gas-condensate fields. The difference between average values of gradient for all of field types is statistically significant. Therefore, we indicate appearance of geothermal quantitative criterion for forecasting fluid type of deposits in areas of high potential for hydrocarbons. Quantitative relation of high significance (r=0,53) between heat flow density and hydrocarbon density is established for high heat flow values (&gt;56 mW/m2). Weak correlation (r=0,3) was indicated between horizontal gradient of heat flow and hydrocarbon density.

Evaluation of Geothermal Energy Potential in Parts of the Lower Benue Trough, Nigeria, Using Aeromagnetic Data

Abstract Nine sheets of Regional Aeromagnetic data of parts of Lower Benue Trough were evaluated through the use of Centroid and forward modelling of the spectral peak methods with a view to delineating structures and basin geometry of the Southern (Lower) Benue Trough of Nigeria. Geological cross sections were used to determine the number of anomalies from the residual magnetic map after which the Discrete Fourier Transform method was applied in calculating and computing the depth to the top (Zt), depth to the bottom (Zo), Curie point depth (CPD), geothermal gradient and heat flow. From the results, the depth to the top of the magnetic source ranges between 0.5km and 12.5km with the highest points towards the south - western part of the study area. The depth to the bottom of magnetic source (centroid depth) ranges from 2km to 54km and the highest areas are located towards the north-eastern part of the study area. The geothermal gradient ranged between 21oC/Km to 29.5oC/Km., Ogoja, Oturkpo, and Katsina–Ala are situated within the region of high geothermal gradients (&gt;26.5oC/Km). The heat flow values range from 22mW/M2 to 74 mW/M2 and the areas with the high heat flow values are Makurdi, Ogoja, Gboko and Katsina-Ala. The results also show that the Curie temperature isotherm within the study area is not a horizontal level surface, but it is undulating. The study also identified high sedimentary thickness and considerable geothermal potential which could serve as a basis for hydrocarbon accumulation and geothermal exploitation. Keywords: Geothermal Gradient, heat flow, Crustal Temperature, Geothermal Potentials, Total Magnetic Intensity (TMI).

Three-Dimensional Electromagnetic Imaging of Geothermal System in Gonghe Basin

To better understand the geothermal system of the Gonghe Basin, we deployed 471 magnetotelluric survey points with an average distance of 2~3 km, covering the eastern and southern areas of the Basin. We used ModEM inversion software to carry out 3D inversion of 431 survey points and established a 3D-electrical model at a depth of 50 km in the area. The resistivity model shows that the low resistivity in the shallow part of the basin is related to the Cenozoic loose sedimentary cover, while the resistivity values of the mountains around the basin and the magmatic rock uplift zone are higher. The electrical model also shows that the high-conductivity layer is widely distributed in the middle and lower crust (15~35 km) of the basin, and direction of the high-conductivity layer is consistent with that of NW–SE fault in the basin. These high-conductivity layers may be the principal reason for the high heat flow values in the Gonghe Basin. Our resistivity model also shows that there is an obvious discontinuity between high- and low-resistivity blocks at different depths in the middle and upper crust. These discontinuities are consistent with the faults observed on the surface, which are related to the strong topographic relief. Our electrical model shows that these faults in the middle and upper crust are connected with the high-conductivity layer as the channel of heat transfer to the shallow part. Finally, the heat energy is enriched in the Triassic granite to form dry hot rock (HDR). The 3D-magnetotelluric imaging results depict the 3D-distribution characteristics of the geothermal system in the eastern and southern parts of the Gonghe Basin.

Distribution of surface heat flow and effects on the subsurface temperatures in the northern part of Thrace Basin, NW Turkey

The Thrace Basin in northwestern Turkey is a deep Eocene–Oligocene hydrocarbon-bearing sedimentary basin. The basin has potential for geothermal energy utilization in the future due to its favorable geological conditions. In this study, we combined the available bottom hole temperature (BHT) data from 70 points with the thermal conductivity and radiogenic heat productions of the basin formations, and generated a detailed thermal model of the northern part of the basin. For heat flow determinations from the BHT data, we applied Bullard’s thermal resistance method on formation thermal conductivities and thicknesses. The results give an average surface heat flow of 65.8 ± 11.3 mW/m2. We obtained high heat flow values (75–80 mW/m2) in the eastern and western sides, and the central part of the study area. These relatively high heat flow values can be explained by the combined effect of basement topography and the variations in the radiogenic heat production of the basement rocks. The calculated subsurface temperatures in selected hydrocarbon fields vary in the range of 45–64 °C at 1 km depth, 99–136 °C at 3 km depth, and 155–208 °C at 5 km depth as a result of local variations of the surface heat flow and formation thermal resistances. These variations in subsurface temperatures can have significant effects on the cost of geothermal energy production in future.

Predicting Terrestrial Heat Flow in North China Using Multiple Geological and Geophysical Datasets Based on Machine Learning Method

Geothermal heat flow is an essential parameter for the exploration of geothermal energy. The cost is often prohibitive if dense heat flow measurements are arranged in the study area. Regardless, an increase in the limited and sparse heat flow observation points is needed to study the regional geothermal setting. This research is significant in order to provide a new reliable map of terrestrial heat flow for the subsequent development of geothermal resources. The Gradient Boosted Regression Tree (GBRT) prediction model used in this paper is devoted to solving the problem of an insufficient number of heat flow observations in North China. It considers the geological and geophysical information in the region by training the sample data using 12 kinds of geological and geophysical features. Finally, a robust GBRT prediction model was obtained. The performance of the GBRT method was evaluated by comparing it with the kriging interpolation, the minimum curvature interpolation, and the 3D interpolation algorithm through the prediction performance analysis. Based on the GBRT prediction model, a new heat flow map with a resolution of 0.25°×0.25° was proposed, which depicted the terrestrial heat flow distribution in the study area in a more detailed and reasonable way than the interpolation results. The high heat flow values were mostly concentrated in the northeastern boundary of the Tibet Plateau, with a few scattered and small-scale high heat flow areas in the southeastern part of the North China Craton (NCC) adjacent to the Pacific Ocean. The low heat flow values were mainly resolved in the northern part of the Trans-North China Orogenic belt (TNCO) and the southmost part of the NCC. By comparing the predicted heat flow map with the plate tectonics, the olivine-Mg#, and the hot spring distribution in North China, we found that the GBRT could obtain a reliable result under the constraint of geological and geophysical information in regions with scarce and unevenly distributed heat flow observations.

Correlations between seismic b-value and heat flow density in Vlora-Lushnja-Elbasani-Dibra Fault Zone in Elbasani area, central Albania

In this study, the correlations between the heat flow density and seismotectonic b-value in the Elbasani area of Albania were investigated to understand the how low-velocity layers underneath the Elbasani area in central Albania struggling the large-scale Vlora-Lushnja-Elbasani-Dibra Fault Zone affect the heat flow data. For this purpose, the heat flow and regional distribution of b-value were imaged for different locations and depths. To achieve the analysis, the Albanian Seismological Catalogue for the period between 1 July 1968 and 26 December 2022, including 1830 earthquakes with a local magnitude of 0.5 ≤ Ml ≤ 5.2 that occurred at the depths below 70 kilometres, was considered. The b-value was calculated as 1.03 ± 0.06 by considering the magnitude of the completeness value as Mc-value = 2.6. This result shows that the b-value of earthquake distribution in the Vlora-Lushnja-Elbasani-Dibra (VLED) fault zone is well represented by the Gutenberg and Richter (G-R) scaling law with the b-value close to 1.0. The regional variations of the b-value show that b-values smaller than 0.9 were observed in the western and south-western parts of the Llinxha-Kozan thermal water belt. The depth distribution of the b-value indicates that there exists a sharp decrease in the b-values from 1.15 to 0.7 in the depths varying from 5 to 20 km. The highest heat flow values were observed on the Dumrea diapiric dome and in the central part of the Elbasani area. Thus, our analysis indicates significant and robust correlations between the geothermal and earthquake distribution. The discontinuity of Moho interface is deep in the regions where high b-values were observed. Low b-values are found at the depths ranging from 20–25 km and 35–40 km in the Dumrea evaporite massif area. We have evidence that high b-values and large heat flow values are related to the low seismic velocity layers underneath the Elbasani area. The low-velocity zone (LVZ) in Albania occurs in the Earth’s crust and in the upper mantle. It is characterized by an unusually low seismic shear wave velocity compared to the surrounding depth intervals. It is well known that the low-velocity layers in the Elbasani area are determined in the upper crust, at shallow depths of 2–4 km, and in the middle crust at a 10–14 km depth. Hence, it is suggested that the Moho interface in the eastern part of the Elbasani area is relatively deep (45 km) compared to the western part of Albania (35 km), and the magnitude of earthquakes is smaller where the high heat flow values were observed.

Determination of Conrad and Curie point depth relationship with the variations in lithospheric structure, geothermal gradient and heat flow beneath the central main Ethiopian rift

Spectral analysis of the pole reduced magnetic anomaly data and inversion of complete Bouguer anomaly data are employed here as there is no previous published data regarding for the determination of the Curie point depth (CPD), Conrad depth (CD) and lithospheric mantle thickness in the central main Ethiopian rift (CMER) and its environs. The results confirm that the CPD, range between 7.68 and 20.3 km, CD, range between 16 and 25 km and lithospheric mantle thickness, range between 13.4 and 27. 8 km. These results indicate that the CMER magnetic crust occur close to the CD and lithospheric mantle thickness, but below the Moho depth beneath the study area. Based on the results on CPD, we estimate the magnitude of the geothermal gradient and heat flow in the study area. The results confirm that the geothermal gradient, range between 32.4 and 65 °C km−1 and heat flow, range between 80 and 160 mWm-2. These results are found to be inversely correlated with the CPD. It is a commonly known fact that shallow CPDs generate negative magnetization. Similarly, in this study, it is recorded low magnetic anomalies overlap with shallow (less than 13.1 km) CPDs in line with high (110–160 mWm−2) heat flow and high (48–64 °C km−1) geothermal gradient values are determined to occur beneath the CMER. These results associate with the presented geotectonic and geothermal signatures of the study area.

The dynamic floor of Yellowstone Lake, Wyoming, USA: The last 14 k.y. of hydrothermal explosions, venting, doming, and faulting

AbstractHydrothermal explosions are significant potential hazards in Yellowstone National Park, Wyoming, USA. The northern Yellowstone Lake area hosts the three largest hydrothermal explosion craters known on Earth empowered by the highest heat flow values in Yellowstone and active seismicity and deformation. Geological and geochemical studies of eighteen sublacustrine cores provide the first detailed synthesis of the age, sedimentary facies, and origin of multiple hydrothermal explosion deposits. New tephrochronology and radiocarbon results provide a four-dimensional view of recent geologic activity since recession at ca. 15–14.5 ka of the &amp;gt;1-km-thick Pinedale ice sheet.The sedimentary record in Yellowstone Lake contains multiple hydrothermal explosion deposits ranging in age from ca. 13 ka to ~1860 CE. Hydrothermal explosions require a sudden drop in pressure resulting in rapid expansion of high-temperature fluids causing fragmentation, ejection, and crater formation; explosions may be initiated by seismicity, faulting, deformation, or rapid lake-level changes. Fallout and transport of ejecta produces distinct facies of subaqueous hydrothermal explosion deposits. Yellowstone hydrothermal systems are characterized by alkaline-Cl and/or vapor-dominated fluids that, respectively, produce alteration dominated by silica-smectite-chlorite or by kaolinite. Alkaline-Cl liquids flash to steam during hydrothermal explosions, producing much more energetic events than simple vapor expansion in vapor-dominated systems. Two enormous explosion events in Yellowstone Lake were triggered quite differently: Elliott’s Crater explosion resulted from a major seismic event (8 ka) that ruptured an impervious hydrothermal dome, whereas the Mary Bay explosion (13 ka) was triggered by a sudden drop in lake level stimulated by a seismic event, tsunami, and outlet channel erosion.

Regional thermal anomalies derived from magnetic spectral analysis and 3D gravity inversion: Implications for potential geothermal sites in Tanzania

Tanzania is one of the several countries intersected by the East African Rift System (EARS) endowed by a geothermal potential that has been explored only to a limited extent. Here we present the first heat flux map over the region based on the Curie point depth (CPD) estimation from aeromagnetic data. We have estimated the base of magnetic sources as a proxy for the CPD from the radially average power spectra of the total magnetic field using the centroid and the de-fractal methods. Our results show that the CPDs range ca. 11 to 43 km and are comparable to, but more detailed than global CPD estimates. The heat flow has then been computed assuming a constant thermal conductivity. In order to evaluate the results against crustal thickness, we have inverted the gravimetric regional field data constrained by the existing Moho depth from seismic receiver functions. Our analysis has revealed high heat flow values (over 100 mW/m2) along the EARS and at the Proterozoic collision boundaries that have been reactivated by the EARS. In general, the high heat flow anomalies coincide with known surface geothermal manifestations and shallow Moho depth in the range ca. 30 to 35 km. A high heat flow anomaly is also found in the central part of the Tanzanian craton, likely related to the mantle plume imaged by seismic tomography. The most interesting areas for geothermal exploration in Tanzania, according to our results, are the EARS triple junction in the Rungwe volcanic province, the north Tanzania divergent zone and the areas of the Proterozoic collision boundaries reactivated by the EARS.

Occurrence Mechanism of Convective Geothermal Systems in Jiaodong Peninsula, China

Previous studies have shown that on the surface, Jiaobei uplift and Weihai uplift have higher heat flow values than Jiaolai depression. However, the mechanism by which the deep heat flow migrates and the exposure of geothermal resources are still unclear. In this study, the geothermal field distribution, thermal conductivity, temperature logging data, and chemical composition of the geothermal fluid in the Jiaodong Peninsula were analyzed. Regarding the thermal field’s characteristics and their controlling factors, a conceptual model of heat flow diversion-accumulation between the uplift and basin areas in the Jiaodong Peninsula is proposed. The lithology of the uplift area is mainly composed of intrusive rocks and metamorphic rocks with high thermal conductivities. The lithology of the basin mainly consists of sandstone with a low thermal conductivity. The bottom of the basin, which has a low thermal conductivity and low permeability, serves as a heat insulation and water insulation roof, which causes the heat flow and the heat-carrying fluids and gases from the deep crust to be refracted and redistributed at the bottom of the basin area. As a result, the bottom of the uplift areas has a higher heat flow. In particular, the axial position in the uplift area has the highest heat flow. In addition, the geothermal resources in the Jiaodong Peninsula are mainly distributed in the V-shaped area where the upper block of the NE- and NW-trending faults intersect, and the scope of the exposure of the geothermal resources is very limited.

The role of geotectonic setting on the heat flow distribution of southern South America

SUMMARYThe surface heat flow of southern South America was examined based on an updated database containing 1113 locations. Accordingly, this study presents the most accurate heat flow map of the southern portion of the continent (south of 16°30′S latitude), covering areas that previously presented limited information. The main anomalies show a strong spatial correlation with geothermal zones and with the most up-to-date lithospheric thickness maps. The blanketing effect produced by the sedimentary basins reduce the surface heat flow up to 27 mW m–2 over the thickest basins. The study region was separated into four large areas and their connection to tectonic processes analysed. The Central Andes present high heat flow zones related to a thick radiogenic crust, volcanic activity, and a hot asthenospheric wedge. In the Pampean flat-slab region, the low heat flow coincides mostly with the horizontal projection of the Juan Fernández aseismic ridge and not with a wide region as previously thought. Furthermore, a close relationship between the subduction of the ridges at different angles and a cold upper-plate lithosphere is suggested. Besides active regions of arc magmatism and a thin lithosphere, we propose that a hot upper-plate upwelling beneath the Patagonian Platform is also contributing to the high heat flow in the area. The foreland region exhibits a low heat flow coinciding with a thick cratonic lithosphere, and local high heat flow values in suture zones possibly triggered by ancient delamination beneath these regions.

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.

Study of the Geothermal Potential of the Locality of Kaladi and Its Surroundings (Adamawa-Cameroon) from the Frequency Processing of Magnetic Data

The aim of this study is to estimate the variations in curie point depth, geothermal gradient and heat flux from the frequency analysis of magnetic data in order to evaluate the geothermal potential of the Kaladi locality and its surroundings. For this purpose, the magnetic field map was first reduced to equator (RTE). The centroid method was used to divide the RTE grid into a set of 40 blocks. The spectral analysis applied to each block allowed determining the depth to top (Zt), center (Z0) and bottom (Zb also called curie point depth or CPD) of the magnetic sources. Knowing the different CPD, the geothermal gradient associated with each block was calculated. The heat flow was then calculated from the geothermal gradient associated with the anomaly block considered. From the set of values obtained for each block, maps of geothermal gradient and heat flow variations were established. Analysis of these maps shows that the sectors that could be favourable for geothermal exploration are the north of Kaladi and the Goro-Bembara corridor, because they show variations in the geothermal gradient and heat flow between 0.4 and 0.8℃/m and between 1.2 and 2 mW/m2 respectively. In addition, the superposition of the different hot springs highlighted in previous studies with areas of high geothermal gradient and heat flow values supports this analysis. The proposed models can be used as background documents for any geothermal exploration project in the study area.

Assessment of petroleum system elements and migration pattern of Borno (Chad) Basin, northeastern Nigeria

Borno (Chad) Basin is an intra-cratonic rift basin located at the southwestern terminal of the West Africa Rift System. Despite its reported low petroleum potential, oil seepages have recently been found in the basin from its oldest and lowest stratigraphic unit, the Bima Sandstone. The lack of source beds below this reservoir sandstone makes it challenging to classify the basin petroleum system elements (PSEs) in their normal order and to predict the origin of the oil seepages in the region. Coupled structural analysis (2D Move) and petroleum system modeling (PetroMod) were employed to investigate the structural and hydrocarbon evolution of the basin to reassess its PSEs, hydrocarbon potential and migration trends. The structural model shows that the basin has extended up to 2900 km since the Late Cretaceous. The extension controlled by regional tectonic activities has affected the West and Central Africa Rift System and caused some localized tectonic disturbance in the form of igneous underplating and magmatic intrusion, leading to regional uplift. The magmatic sill intruded into the Late Cretaceous source rock formations increased the heat flow for the study area to a peak value of 128 mW/m2. This anomalous high heat flow value is 38 mW/m2 above the regional average and 18 mW/m2 above the average value for a non-volcanic rift margin. Essential petroleum system elements for trapping and accumulation of hydrocarbons were missing as a result of the uplift during the Late Cretaceous, creating hiatus and diverting sediments to other parts of the basin. The PetroMod model result indicates three zones of oil generation: Early Oil, Main Oil, and Late Oil in the Fika Shale and the Gongila source formations. Source rocks became mature at a relatively shallow burial depth of 900 m due to transient heating from the magmatic sill intrusion in the Late Cretaceous. Oil migrated updip to the surface through fault breakouts. The modeling results show no significant entrapment of conventional hydrocarbons in the study area. The findings improve our understanding of the Borno Basin petroleum system setting and offer new insight on the petroleum exploration potential in the region.