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[en] The N-E Sardinia batholith is part of the European Variscan belt which is generally considered an example for hot collisional orogens. After a period of crustal thickening characterized by lower gradients, during Late Carboniferous and Early Permian times, higher geothermal gradients were diffusively established. The sources which contributed to the thermal budget of late Variscan high-temperature events are still debated. One of the hypothesis(1) considers an extra contribution by radioactive heating of felsic crust tectonically emplaced at the bottom of a Palaeozoic orogenic root. It is apparent that a detailed characterization of heat-producing elements (K, U and Th) of Sardinian Variscan crust are needed by the Earth Science community. This study focus on this goal reporting the results of an extensive survey on the base of gamma-ray measurements performed in the laboratory and in situ. The K, U and Th abundances obtained for the main lithotypes of Sardinia batholiths will be used as input for modeling the geodynamic and thermal evolution of the South Variscan Belt
[en] There are generally three main sources of temperature data-BHT data from log headers, production temperature data, and continuo's temperature logs. Analysis of continuous temperature profiles of over 100 wells in the Niger Delta two main thermal models (single leg and dogleg) are defined with occasional occurrence of a modified dogleg model.The dogleg model is characterised by a shallow interval of low geothermal gradient (<2C/100m) and a deeper interval of high geothermal gradient (>3.0.C/100m). This is characteristically developed onshore area is simple, requiring only consideration of heat transients, modelling in the onshore require modelling programmes with built in modules to handle convective heat flow dissipation in the shallow layer. Current work around methods would involve tweaking of thermal conductivity values to mimic the underlying heat flow process effects, or heat flow mapping above and below the depth of gradient change. These methods allow for more realistic thermal modelling, hydrocarbon type prediction, and also more accurate prediction of temperature prior to drilling and for reservoir rock properties. The regional distribution of the models also impact on regional hydrocarbon distribution pattern in the Niger Delta
[en] Forty apatite samples of sandstone from ten exploration wells in the Scotian Basin, offshore Nova Scotia, Canada, were used for fission track analysis and thermal history reconstruction. The sample depths range from 1000 to 5500 m. Fission tracks in all apatite samples are at least partially annealed. Apatite fission track ages for the the shallowest samples, from the Logan Canyon Formation, are older than their stratigraphic ages and therefore retain some record of cooling in the detrital source area. samples from deeper formations (Mississauga, Mic Mac and Verrill Canyon) have apatite fission track ages younger than their stratigraphic ages (some give zero ages), indicating partial to total annealing of fission tracks in apatite. The degree of annealing in most samples modelled is significantly higher than would be expected given their present-day temperatures. This indicates that these samples experienced a thermal overprint; they have been hotter in the past than at present. Inverse modelling by a Constrained Random Search (CRS) technique was carried out on the six best data sets. The results indicate that strata at depths of 1650-2600 m in the modelled wells were heated to paleotemperatures of about 80-110oC at some time during the interval 100-40 Ma. The magnitude of the thermal overprint predicted (estimated) by the modelling ranges from 1o to 55oC among the five wells modelled. Zircon fission track data from fifteen samples in four wells do not constrain burial temperatures. These data indicate a mixed provenance for the sediments. (author). 71 refs., 3 tabs., 7 figs
[en] Permafrost accounts for about 52% of the total area of the Qinghai-Tibet Plateau, and the permafrost area is about 140 x 104 km2. The mean annual ground temperature of permafrost ranges from -0.1 to -5 deg. C, and lower than -5 deg. C at extreme high-mountains. Permafrost thickness ranges from 10 to 139.4 m by borehole data, and more than 200 m by geothermal gradients. The permafrost geothermal gradient ranges from 1.1 deg. C/100 m to 8.0 deg. C/100 m with an average of 2.9 deg. C/100 m, and the geothermal gradient of the soil beneath permafrost is about 2.8-8.5 deg. C/100 m with an average of 6.0 deg. C/100 m in the Qinghai-Tibet Plateau. For a minimum of permafrost geothermal gradients of 1.1 deg. C/100 m, the areas of the potential occurrence of methane hydrate (sI) is approximately estimated to be about 27.5% of the total area of permafrost regions in the Qinghai-Tibet Plateau. For an average of permafrost geothermal gradients of 2.9 deg. C/100 m, the areas of the potential occurrence of methane hydrate (sI) is approximately estimated about 14% of the total area of permafrost regions in the Qinghai-Tibet Plateau. For the sII hydrate, the areas of the potential occurrence of sII hydrate are more than that of sI methane hydrate.
[en] A geothermal gradient is one of the most frequently used parameters in logging geophysics. However, the drilling process greatly disturbs the temperature of the formations around the wellbore. For this reason, in order to determine with the required accuracy the formation temperatures and geothermal gradients, a certain length of shut-in time is required. It was shown earlier (Kutasov 1968 Freiberger Forshungshefte C 238 55–61, 1987 Geothermics 16 467–72) that at least two transient temperature surveys are needed to determine the geothermal gradient with adequate accuracy. However, in many cases only one temperature log is conducted in a shut-in borehole. For these cases, we propose an approximate method for the estimation of the geothermal gradient. The utilization of this method is demonstrated on four field examples
[en] Cretaceous rocks of Indus Basin of Pakistan are dominated by clastics with subordinate limestone towards the top. These rocks represent shelf facies and were deposited in deltaic to reducing marine conditions at variable depths. Indications of a silled basin with restricted circulation are also present. Cretaceous fine clastics/carbonates have good source and reservoir qualities. Variable geothermal gradients in different parts of basin have placed these rocks at different maturity levels; i.e. from oil to condensate and to gas. The potential of these rocks has been proved by several oil and gas discoveries particularly in the Central and Southern provinces of Indus Basin. (author)
[en] Sandstone drill core and/or cuttings from six wells in the Gulf of St. Lawrence and cabot Strait have been analyzed using the apatite fission track (AFT) method. Measured AFT ages for the late Paleozoic sandstones range from 26 ±7 to 184 ±28 Ma (2-σ errors). The AFT data indicate that most Maritimes Basin strata were heated to temperatures in excess of 100-150oC very soon after their deposition. The strata also attained significant vitrinite reflectance (R0) levels (i.e., reaching the oil window) early in the burial history. These findings imply the generation of hydrocarbons and coalbed methane in the early basin history (pre-250 Ma). In the Maritimes Basin AFT and R0 data provide complementary information about the integrated thermal history, including maximum burial temperatures (from R0 data), and information on the subsequent cooling history from AFT analysis. The present study also supports the proposal made previously by others that substantial erosion of the Eastern Canadian margin (up to 4 km) has occurred since the Permian and extends the AFT evidence for this erosional event to include the southern Gulf of St. Lawrence area. Thermal models of the AFT data demonstrate that they are consistent with a history of exhumation of basin strata since late Permian time. The model-predicted AFT age and track length histograms closely correspond to the measured AFT parameters. AFT analysis also indicates present-day geothermal gradients of less than 40oC/km. (author). 42 refs.,3 tabs., 7 figs
[en] Whereas luminescence dating applications usually avoid gradients and therefore surfaces, this study explores the requirements and possibilities of dating surfaces using infrared stimulated luminescence. The basic prerequisite for dating applications is a dose-dependent, bleachable and stable luminescence signal. It was found to be fulfilled for crushed granite rock material. Depth profiles below polished surfaces of granites indicate that a well bleached layer below the actual surface solely contributes to the infrared stimulated luminescence signal. A new measurement device, designed for in situ surface dating applications, is presented along with first experimental results
[en] A Curie surface indicates the distribution of the thermal fields underground, providing a clear marker for the thermodynamic effect in the crust and mantle. In this paper, based on a geomagnetic field model (NGDC-720) and aeromagnetic data, we use power spectrum analysis of magnetic anomalies to estimate the Curie surface in Yunnan Province, China, and its adjacent areas. By combining the distribution of the Curie surface with regional heat flow, the geothermal gradient, crustal wave velocity ratio anomalies, high-conductivity layer anomalies, and the Moho surface, we reveal the connection between the undulation of the magnetic basement and the crustal structures. The results indicate that the uplift and depression of the Curie surface in the research area are distinct. The Curie surface is approximately inversely correlated to the surface heat flow. The Lijiang-Jianchuan-Baoshan-Tengchong and Jianchuan- Chuxiong- Kunming-Yuxi zones are two Curie surface uplift zones, and their crust-mantle heat flows are relatively high. The Curie surface uplift zone along the Lijiang-Xiaojinhe fault and Red River fault is consistent with the heading direction of the fault zone and is partially in agreement with the eastward mass flow of the Tibetan Plateau. The Curie surface uplift zone is consistent with the high wave velocity ratio and high-conductivity layer anomaly region of the crust. The depth of the Curie surface is less than the depth of the Moho surface. .
[en] Highlights: • Qiangtang Basin is the biggest residual petroleum-bearing basin in Tibet Plateau. • The Late Triassic Tumen Gela Formation is the most important gas source rock. • Seventy-one potential anticline structural traps have been found. • A favorable geothermal condition for gas hydrate formation. • A large number of mud volcanoes were discovered in the basin. - Abstract: The Qiangtang Basin is the biggest residual petroleum-bearing basin in the Qinghai–Tibet Plateau, and is also an area of continuous permafrost in southwest China with strong similarities to other known gas-hydrate-bearing regions. Permafrost thickness is typically 60–180 m; average surface temperature ranges from −0.2 to −4.0 °C, and the geothermal gradient is about 2.64 °C/100 m. In the basin, the Late Triassic Tumen Gela Formation is the most important gas source rock for gas, and there are 34.3 × 108 t of gas resources in the Tumen Gela Formation hydrocarbon system. Seventy-one potential anticline structural traps have been found nowadays covering an area of more than 30 km2 for each individual one, five of them are connected with the gas source by faults. Recently, a large number of mud volcanoes were discovered in the central Qiangtang Basin, which could be indicative of the formation of potential gas hydrate. The North Qiangtang depression should be delineated as the main targets for the purpose of gas hydrate exploration