Average Heat Flow Values Research Articles

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 (<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.

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 (>56 mW/m2). Weak correlation (r=0,3) was indicated between horizontal gradient of heat flow and hydrocarbon density.

Utilization of mine waste heat in phase change rechargeable battery

Mine geothermal energy has been recognized as “heat hazard”, which is harmful to the health of miners and causes disasters. In order to realize the transformation of mine geothermal energy and waste heat from “hazard/waste” into “treasure”, this paper analyzes the distribution characteristics and genesis of mine geothermal energy with the field geothermal temperature monitoring data, evaluates geothermal reserves, and reveals the mutual influencing mechanism of stratified exploitation of two-layer geothermal reservoir and the law of thermal energy conduction and evolution in the stope of geothermal-coal synergetic mining (GE-COSM), using numerical models verified by experiments. In the end, the improvement effect of mine waste heat on the development potential of geothermal-coal mine (G-CM) was analyzed. The result shows that: The present geothermal field distribution characteristics of Anju Mine are high in the north and low in the south, high in the east and low in the west. There are two layers of zoned reservoir, with the temperatures of 43 °C and 54 °C respectively, the average heat flow value 70.1 mW/m2 and 80.9 mW/m2 respectively, and the geothermal water type SO42--Na+·Ca2+. The simultaneous exploitation of the two geothermal reservoirs will form a Coal-Austria geothermal reservoir joint influence area(C-Area) with lower temperature, which reduces the harm of “heat hazard” to miners. But the phase change heat storage function of functional cemented paste backfill material for phase change heat storage (F-CBM) is not fully utilized in the late stage of geothermal exploitation. The mine generates 4.6 × 1011 J of waste heat per day, and according to the type of heat source of mine waste heat can be continuously “heat charging” for a conventional backfill working face. Moreover, under the action of high temperature surrounding rock, the thermal energy recovery rate is greater than 1, and under the action of “heat charging”, the average maximum value of solid phase ratio is greater than 70 %. Therefore, the phase change rechargeable battery mode creatively proposed by this paper is significantly better than the traditional rock layer heat storage mode and is worth vigorously popularizing.

Exploration Process and Genesis Mechanism of Deep Geothermal Resources in the North Jiangsu Basin, East China: From Nothing to Something

Geothermal resources, as an important member of clean renewable energy, of which the exploration, development, and utilization of geothermal resources, especially deep geothermal resources, are of great significance for achieving carbon peaking and carbon neutrality. Taking the North Jiangsu Basin (NJB) as an example, this paper reviews the exploration process of deep geothermal resources in the basin and presents the latest results. The study shows that the NJB is a typical “hot basin” with an average heat flow value of 68 mW/m2. In this region, the deep geothermal resource favorable areas in the NJB are mainly distributed in the depressions, in particular those near the Jianhu uplift, i.e., the Yanfu depression and the Dongtai depression. In addition, the genesis mechanism of the deep geothermal resource favorable area in the NJB is best explained by the “two stages, two sources” thermal concentration, that is, “two stages” means that the transformation of the lithospheric thermal regime are caused by the late Mesozoic craton destruction in East China, and the Cenozoic lithospheric extension; these two tectono-thermal events together lead to the deep anomalous mantle-source heat (the first source), and the upper crustal-scale heat control is mainly caused by thermal refraction (the second source). Overall, this case study underlines new ideas of understanding the geothermal genesis mechanism in East China, which can guide for the exploration and development of deep geothermal resources at the basin scale.

Antarctic Geothermal Heat Flow Model: Aq1

AbstractWe present a refined map of geothermal heat flow for Antarctica, Aq1, based on multiple observables. The map is generated using a similarity detection approach by attributing observables from geophysics and geology to a large number of high‐quality heat flow values (N = 5,792) from other continents. Observables from global, continental, and regional datasets for Antarctica are used with a weighting function that allows the degree of similarity to increase with proximity and how similar the observables are. The similarity detection parameters are optimized through cross correlation. For each grid cell in Antarctica, a weighted average heat flow value and uncertainty metrics are calculated. The Aq1 model provides higher spatial resolution in comparison to previous results. High heat flow is shown in the Thwaites Glacier region, with local values over 150 mW m−2. We also map elevated values over 80 mW m−2 in Palmer Land, Marie Byrd Land, Victoria Land and Queen Mary Land. Very low heat flow is shown in the interior of Wilkes Land and Coats Land, with values under 40 mW m−2. We anticipate that the new geothermal heat flow map, Aq1, and its uncertainty bounds will find extended use in providing boundary conditions for ice sheet modeling and understanding the interactions between the cryosphere and solid Earth. The computational framework and open architecture allow for the model to be reproduced, adapted and updated with additional data, or model subsets to be output at higher resolution for regional studies.

Heat Flow on the U.S. Beaufort Margin, Arctic Ocean: Implications for Ocean Warming, Methane Hydrate Stability, and Regional Tectonics

AbstractResults from the first focused heat flow study on the U.S. Beaufort Margin provide insight into decadal‐scale Arctic Ocean temperature change and raise new questions regarding Beaufort Margin evolution. This study measured heat flow using a 3.5‐m Lister probe at 103 sites oriented along four north‐south transects perpendicular to the ~700‐km long U.S. Beaufort Margin. The new heat flow measurements, corrected both for seasonal ocean temperature fluctuations and bathymetric effects, reveal low average heat flow values (~35 mW/m2) at seafloor depths of 300–900 m below sea level (mbsl) and anomalously high (~80 mW/m2) values at seafloor depths of >1,000 mbsl, near the predicted continent‐ocean transition. Anomalously low heat flow values measured on the upper margin are consistent with previous studies suggesting decadal‐scale ocean temperature warming to ~500 mbsl. Our results, however, indicate this ocean warming likely extends to depths as great at 900 mbsl—400 m deeper than previous studies suggest—implying widespread, ongoing, methane hydrate destabilization across much of the U.S. Beaufort Margin. The cause of the anomalously high heat flow values observed at seafloor depths >1,000 at the continent‐ocean transition is unclear. We suggest three candidate processes: (1) higher heat production and lower thermal conductivity on the margin edge due to the thickest sedimentary cover at the ocean‐continent transition, (2) seaward migrating subsurface advection, and (3) possible fault‐reactivation at the northern boundary of the Alaskan Microplate.

Optimization on non-transparent envelopes of the typical office rooms with air-conditioning under intermittent operation

In present energy conservation design, air-conditioning operation is deemed to be continuous in the whole building, but the intermittent operation of air-conditioning is widely applied due to the occupant’s behaviour. The large discrepancy in the energy efficiency and energy consumption can cause between the actual usage and the primary design. Considering this situation, a numerical simulation was carried on to optimize the thermal performance of non-transparent envelope components in three typical rooms with air-conditioning under the intermittent operation in summer. The energy-saving potential of all components was analysed, while the whole heat transfer capacities in three typical rooms were compared between traditional and optimized envelopes. Results showed by optimizing envelope components, the average heat flow values could be reduced by up to 13.78–71.27%, while the average heat transfer capacities were reduced by 33–39% and their fluctuation percentages were also decreased obviously. Compared to interior and exterior walls, floors and ceilings had the higher energy-saving contribution percentages of 35–80% and the larger the room area, the larger the energy-saving contribution percentage of floors and ceilings.

Estimation of Curie Point Depth (CPD) across the Pan African Belt in Northern Cameroon from Aeromagnetic Data

The depth to the Curie isothermal point (CPD) was estimated using aeromagnetic data from northern Cameroon. The CPD was estimated using a two-dimensional power density spectral analysis of nineteen 30 × 30 km blocks over a series of Neoproterozoic lithologies associated with the Pan African orogeny. The results show that there are two main regions characterized by the CPD analysis: 1) Shallow depths (~6.37 - 10.09 km) which are located in several regions including the northern portions of the study area (toward the regions of Hina Marbak, Gawel and northern Moutouroua), the southeast (Kaele region), the south (Guider) and the southwest (Mayo Oulo), and 2) deeper depths (~10.68 - 13.72 km) are located in the northeast (Mindif) and southwest (southern Moutouroua, Guider and Bossoum). The shallow depths can be related to two tectonic regimes: 1) the West-Central African Rift System with northeast-trending strike-slip faults emanating from the Gulf of Guinea and 2) the Cameroon Volcanic Line. However, the ultimate source of these shallow regions is interpreted to be related to the Cameroon Volcanic Line based on low seismic velocities imaged by recent broadband seismic studies which are concentrated along the northeast-trending strike-slip faults. An additional finding using the CPD depths, a Curie isothermal temperature of 580&#176C and a one-dimensional heat flow model, was heat-flow values ranging from 105.68 to 227.63 mW/m2, which are above average global heat flow values and are therefore indicative of potential geothermal resources.

Applying Depth Distribution of Seismicity to Determine Thermo-Mechanical Properties of the Seismogenic Crust in Southern California: Comparing Lithotectonic Blocks

We analyze waveform-relocated seismicity (1981–2016) and other geophysical and geological datasets from 16 lithotectonic crustal blocks in southern California. We explore how earthquake depth histograms (EDH) are related to crustal strength, lithology, and temperature of the crust. First, we calculate relative EDHs to quantify the depth distribution of seismicity for each lithotectonic block. Second, we calculate depth profiles of maximum differential stress (“yield strength envelopes”, YSEs) using Byerlee’s law and a non-linear dislocation creep law. We use observed average heat flow values, strain rates, and states of stress to parameterize YSEs for five different crustal candidate lithologies in each lithotectonic block. We assume that seismicity ceases where the mechanical rock strength falls below a critical threshold level, and identify the YSE that best predicts the depth extent of seismicity in each block. The lithologies of the best matching YSEs are found to agree well with expectations from past tectonics: they are mostly quartz-dominated except for the feldspar-rich diorite lithologies in the Great Valley, the southernmost western Sierra Nevada, Inner Continental Borderland, and Rifted crust in the Salton Trough. Similarly, the inferred thermo-mechanical properties, including differential stress, lithology, and geotherms reflect the previously mapped tectonic variability between the 16 lithotectonic blocks. On average, the differential yield stress is smaller and peaks at a shallower depth in hotter and more quartz rich crust but is larger and peaks at greater depths for colder and predominantly diorite crust. The good agreement between the modeled YSEs, the EDHs and tectonic considerations suggests that EDHs indeed reflect long-term geophysical properties of the crust and can be used to infer thermo-mechanical properties at depth. In contrast, shallow seismicity may be more likely to reflect short-term strain transients from fluid flow or recent anthropogenic disturbances.

Geothermal asymmetry in transform faults of the equatorial Atlantic Ocean

Statistical analysis of heat flow values measured in transform faults of the equatorial part of the Atlantic Ocean has been performed. Owing to the calculation using the Cramer–Welch criterion, it was established that not only is there an already known statistically significant difference between heat flow in active and passive zones of transform faults, but there is also an asymmetry in heat flow distribution between the western and eastern branches of passive zones of the fault zones. The western zones in all structures studied are characterized by higher average heat flow values. Two models are proposed to explain this phenomenon.

CLUSTER ANALYSIS OF GEOLOGICAL AND GEOPHYSICAL PARAMETERS OF THE ARCTIC REGION AS THE BASE FOR GEODYNAMIC INTERPRETATION

Cluster analysis is applied for computing stable combinations of geological and geophysical parameters, and areas with such combinations are interpreted as regions that differ in structural and geodynamic features. The shelf areas are distinguished by specific sets and patterns of parameters, including sedimentary cover thickness, tectonic heterogeneity of the basement, heat flow, anomalous magnetic field, and gravity anomalies that reflect the topography of the crust–upper mantle boundary. In the deep oceanic areas, S-wave velocity variations show abnormally ‘cold’ blocks, while the average heat flow values are high. This combination of parameters is typical of transform zones at the junction of the Atlantic and Arctic segments. Superimposed thermal domes are located symmetrically with respect to the axis of the mid-oceanic ridges (MOR). Such domes may occur on the continents located close to MOR. Similar indicators can be revealed along the transition zone to the north of the East Siberian Sea.

Crustal magnetic anomaly in the Ordos region and its tectonic implications

In this paper, the NGDC-720-V3 model is utilized to investigate the distribution of crustal magnetic anomaly and Curie surface in the Ordos block and its surrounding areas. The Curie surface is compared with the regional heat flow, Bouguer anomalies, Moho, and seismicity. The interior block has strong wide-distributed magnetic anomalies, well corresponding to the basement lithofacies. The surrounding areas have weak anomalies of various strikes and intensities. The magnetic anomaly confirms the geological finding that the Yabulai and Bayanhot Basins are small blocks detached from the northern Ordos block. The magnetic anomalies at the satellite altitude reveal that deep materials flow northward from the northeast margin of Tibet Plateau to the Qilian fold belt. The depth of Curie surface ranges from 24 to 42km, and the Ordos block is dominated by Curie surface depth over 32km and average heat-flow value of 44mW/m2. The distribution of Bouguer anomalies is consistent with that of magnetic anomalies. The well correlation between the Curie surface and the seismicity is also explained.

Determination of the Crustal and Thermal Structure of the Erzurum-Horasan-Pasinler Basins (Eastern Türkiye) Using Gravity and Magnetic Data

The Erzurum-Horasan-Pasinler basin, which surrounds Miocene rocks, is oriented approximately E–W and is located in Eastern Anatolia (Turkiye). East Anatolia, where ophiolitic and young volcanic rocks are widespread, is situated in the Alpine–Himalayan fold-thrust fault belt. The NW–SE trending North Anatolian Transform Fault Zone and the NE–SW trending East Anatolian Transform Fault Zone, formed by the compressional regime of East Anatolia, control the main tectonics of the study region. While the Moho and Conrad depths of the study region are 43.0 and 20.9 km, respectively, the average sedimentary thickness has been determined to be 5.2 km by using the power spectrum method. On the other hand, it is found that the depth of the Moho in the region varies from 41.0 to 44.5 km and the depth of the Conrad discontinuity varies between 22 and 26 km, as computed using empirical equations. The basement of the sedimentary layer is calculated to be 6 km by using inversion results applied to the residual gravity data. The Curie point depth and average heat flow value in this region are calculated as 18.0 km and 89.1 m Wm−2, respectively. Geotherm calculations reveal that the Moho temperature is 1,028.0 °C based on the crustal model. The high heat flow values obtained are attributed to tectonic activities and melting of the lithospheric mantle caused by upwelling of the asthenosphere.

Terrestrial Heat Flow in the Qagan Sag, Inner Mongolia

AbstractThe Qagan sag has the largest oil and gas exploration potential in the Inggen‐Ejin Qi basin, Inner Mongolia. The terrestrial heat flow research is still blank in the Qagan sag and rest of the Inggen‐Ejin Qi basin, which seriously restricts the oil and gas resource assessment in the basin. In this work, 107 rock thermal conductivity data of 19 wells were measured and in‐situ corrected, and the rock thermal conductivities of each stratum were obtained by the union average formula. Based on the 9 wells' temperatures, combined with the above rock thermal conductivity data, the geothermal gradients and terrestrial heat flow were calculated. The results show the Qagan sag has the characteristics of the medium temperature field between tectonically stable and active regions, with an average thermal gradient of 33.6 °C/km and an average terrestrial heat flow value of 74.5 mW/m2. This work provides the geothermal data for oil and gas resource assessment of the Qagan sag and other sags of the Inggen‐Ejin Qi basin.

Seismological Aspects of the Abou Dabbab Region, Eastern Desert, Egypt

Located about 24 km from the Red Sea, the Abou Dabbab region is characterized by significant microseismic activity. The seismic history of this region is marked by two moderate magnitude earthquakes, the 12 November 1955 Mb 6.1 and the 2 June 1984 Mb 5.1. The 1955 Mb 6.1 earthquake was the largest recorded event to occur within Abou Dabbab. Woodward Clyde Consultants (1982) computed the first-motion focal mechanism for the 1955 event. The mechanism has a strike-slip faulting solution with a normal dip-slip component. The T -axis has a NNW trend. The two nodal planes that were determined for this event give NNW to NW and ENE to ESE strike directions. Earthquakes in the Abou Dabbab region have shown a tendency to cluster in space and time (Morgan et al. 1981). This pattern suggests that the activity seems to have been mainly controlled by local sources ( e.g. , magmatic intrusion) triggered in turn by regional tectonics (Badawy et al. 2008). The heat flow value in Abou Dabbab is twice the average heat flow value in the Eastern Desert of Egypt (Morgan et al. 1985). El Hady (1993) reported from the distribution of earthquake's focal depths and rheological studies that the brittle-ductile transition in the Abou Dabbab area occurs at a relatively shallow depth range (∼9–1. km). The existence of the brittle-ductile transition in this region can be attributed to shallow asthenospheric intrusion, which causes an increase in the temperature. Recordings of microearthquakes in Abou Dabbab from 1 August to 20 August 2004 from 11 portable instruments show that this region is distinguished by intense spatial clustering (Figure 1A). The error estimated in both horizontal distance and depth is less than 0.3 km (Hussein et al. 2008). The cross-section perpendicular to the activity reflects two main spatial clusters with a …

A Study on Tectono‐Thermal Evolution History of Bachu Uplift in the Tarim Basin

AbstractBachu Uplift is one of the major oil prospect areas in Tarim basin. Its tectono‐thermal evolution significantly influences generation, migration and accumulation of hydrocarbon in this region. In this paper, we reconstructed buried histories of four seismic profiles spanning Bachu Uplift and rebuilt the tectono‐thermal history of this region by solving two‐dimensional heat conduction partial differential equation. During the simulation, we calculated the average heat flow value at Moho by using the “back stripping” method. Then we employed the principle of isostasy to compute the buried depths of Moho during geological periods, finally calculated the basement and surface heat flow of the basin. The numerical results show that the tectono‐thermal histories of this region can be divided into seven stages. The maximum geothermal gradient and heat flow appeared in the Triassic period, with values of 32 °C/km and 73.6 mW/m2, respectively and the minimum is present now with values of 20 °C/km and 46.4 mW/m2, respectively. Because of lateral thermal diffusion since Miocene, the calculated average heat flow value today is slightly greater than the actual value. At last, we discussed the influence of thermal conductivity and heat generation on thermal evolution of a basin.

Heat-flow and hydrothermal circulation at the ocean–continent transition of the eastern gulf of Aden

In order to investigate the importance of fluid circulation associated with the formation of ocean–continent transitions (OCT), we examine 162 new heat-flow (HF) measurements in the eastern Gulf of Aden, obtained at close locations along eight seismic profiles and with multi-beam bathymetry. The average HF values in the OCT and in the oceanic domain (~ 18 m.y.) are very close to the predictions of cooling models, showing that the overall importance of fluids remains small at the present time compared to oceanic ridge flanks of the same age. However, local HF anomalies are observed, although not systematically, in the vicinity of the unsedimented basement and are interpreted by the thermal effect of meteoric fluids flowing laterally. We propose a possible interpretation of hydrothermal paths based on the shape of HF anomalies and on the surface morphology: fluids can circulate either along-dip or along-strike, but are apparently focussed in narrow “pipes”. In several locations in the OCT, there is no detectable HF anomaly while the seismic velocity structure suggests serpentinization and therefore past circulation. We relate the existence of the present day fluid circulation in the eastern Gulf of Aden to the presence of unsedimented basement and to the local extensional stress in the vicinity of the Socotra–Hadbeen fault zone. At the scale of rifted-margins, fluid circulation is probably not as important as in the oceanic domain because it can be inhibited rapidly with high sedimentation rates, serpentinization and stress release after the break-up.

New terrestrial heat flow map of Europe after regional paleoclimatic correction application

Heat flow variations with depth in Europe can be explained by a model of surface temperature changes >10°C. New heat flow map of Europe is based on updated database of uncorrected heat flow values to which paleoclimatic correction is applied across the continent. Correction is depth dependent due to a diffusive thermal transfer of the surface temperature forcing of which glacial–interglacial history has the largest impact. It is obvious that large part of the uncorrected heat flow values in the existing heat flow databases from wells as shallow as few hundreds of meters is underestimated. This explains some very low uncorrected heat flow values 20–30 mW/m2 in the shields and shallow basin areas of the craton. Also, heat flow values in other areas including orogenic belts are likely underestimated. Based on the uncorrected and corrected heat flow maps using 5 km × 5 km grid, we have calculated average heat flow values (uncorrected heat flow: 56.0 mW/m2; SD 20.3 mW/m2 vs. corrected heat flow: 63.2 mW/m2; SD 19.6 m/Wm2) and heat loss for the continental part. Total heat loss is 928 E09 W for the uncorrected values versus corrected 1050 E09 W.

日本海東縁，上越海盆西部メタンハイドレート分布域の熱流量分布

Methane seep activity around the Joetsu Gas Hydrate Field of the western Joetsu Basin, eastern margin of the Japan Sea, was investigated in detail using heat flow measurements. Heat flow was obtained by Ewing-type heat flow probe and SAHF probe with five thermistors at 11-cm intervals using a ROV during nine research cruises in 2004-2008. Average heat flow value obtained on a normal muddy seafloor in this area is 98 ± 13 mW/m2, which is consistent with the ambient heat flow in the Japan Sea. Based on the results of three day's monitoring, temperature fluctuations (> 0.02 K) of bottom water influence sub-bottom temperature at around a depth of 20 cm. Heat flow values greater than 300 mW/m2 were measured not only at the methane venting sites but also in the some areas covered by bacterial mats. This high heat flow value (> 150 mW/m2) is confined to certain areas (several meters to a few tens of meters scale) on the mounds in the Umitaka Spur and the Joetsu Knoll. Therefore, methane migration from the deep subsurface to seafloor occurs on a very local scale, although seismic profiles show the presence of many small faults through gas chimneys just below the mounds. Convex temperature profiles around the gas venting sites indicate the presence of fluid discharges with Darcy's flow velocity of 1.3 × 10-6 m/s and 5.0∼8.6 × 10-7 m/s, respectively. On the other hand, concave temperature profiles, obtained in the “collapsed hydrate zone” on the mounds, may indicate the presence of a recharge zone. Some temperature reversal profiles in areas covered by bacterial mats were probably caused by a lateral fluid movement from a fluid conduit or by the presence of a methane fluid pool. Some apparent negative geothermal gradient anomalies were obtained only in the “collapsed hydrate zone”. Most of these apparent negative anomalies are possibly explained by the influence of bottom water temperature fluctuations. There seem to be some different hydrological regimes in the high methane flux area of the Joetsu Gas Hydrate Field.

Tectonic thermal history and its significance on the formation of oil and gas accumulation and mineral deposit in Ordos Basin

The analyzing data on stratigraphic temperature measurement, thermal conductivity of the strata and radioactive heat production rate show that the present average geothermal gradient in the Ordos Basin is 2.93 °C/100 m, and the average heat flow value is 61.78 mW/m2, which belongs to the mesothermal basin, and the value of the present geothermal gradient and heat flow in the east is higher than that in the west. The sandstone radioactive heat production rate of Zhiluo Group in Dongsheng Uranium deposits of Yimeng uplift is obviously higher in the mudstone, indicating that there exists a uranium anomaly. Based on studies of the present thermal field of the basin, the late-Mesozoic paleotemperature and paleogeothermal gradient are determined by using different kinds of paleotemperature methods. According to the anomaly of the late-Mesozoic paleotemperature gradient and magmatic event age, there was a tectonic thermal event in the early Cretaceous epoch of late-Mesozoic. This article rebuilds tectonic thermal history of different tectonic units by thermal history simulation using basin simulating software. The evolution of oil-gas and coal, and accumulation (mineralization) of mineral uranium are all controlled by the tectonic thermal history in the Ordos basin, especially by the tectonic thermal event that happened in the late Mesozoic. For both the gas source rocks of upper Paleozoic group and lower paleozoic group, the gas was largely generated in the early Cretaceous epoch of the late Mesozoic. The main petroleum generation period for Yanchang Group in Triassic system is the early Cretaceous epoch too, and the highest thermal maturity of the coal of Permo-Carboniferous, Triassic, and Jurassic reaches is the early Cretaceous epoch also. Early Cretaceous epoch is still one of the most important mineralizing periods of uranium.