Continuous Temperature Logs Research Articles

Terrestrial heat flow measurement and numerical simulation of lithospheric thermal structure in western Sichuan, China

The western Sichuan in the eastern Qinghai-Tibet plateau has significant geothermal potential. Heat flow is one of the most important parameters in geothermic, its measurement can help obtain a better understanding of the regional lithospheric thermal structure. In this study, we reported 4 heat flow data based on the continuous steady-state temperature logging and rock thermal conductivity test, including two class-A and two class-D data. Furthermore, we calculated the lithospheric thermal structure by a 2D steady-state thermal conduction equation in COMSOL, analyzing the lateral differences of lithospheric thermal structure in the eastern Qinghai-Tibet plateau. Our study has determined that the heat flow values in the western Sichuan range from 94.7 to 116.2 mW/m2, with a corresponding geothermal gradient of 32.1–37.3 °C/km. Moreover, numerical simulation results indicate significant differences in lithospheric thermal structure between western Sichuan and Sichuan Basin, where the Longmen Shan fault zone is a crucial regional tectonic boundary and a significant temperature gradient zone. Specifically, the Moho temperature in the western Sichuan region ranges from 1000 to 1200 °C with an average temperature of 1060 °C, while the Sichuan Basin ranges from 600 to 700 °C. Besides, the thermal lithosphere thickness in the western Sichuan and the Sichuan Basin is 88–97 km and 105–110 km, respectively. These observations suggest that the western Sichuan region is characterized by high thermal anomaly and provide theoretical evidence for the geodynamic and geothermal development in this area. Finally, we suggest that the high thermal anomaly in western Sichuan is the result of a combination of factors, such as thickened crust, high radioactive heat production, and shear frictional heating from deep fault and so on.

Geothermal gradient variation in the Büyük Menderes Graben: implications for geothermal potential of the graben, Western Anatolia, Turkey

The Büyük Menderes Graben (BMG) is an E-W oriented active extensional geothermal basin within the Menderes Massif, a metamorphic core complex, in Western Anatolia, Turkey. 1500 
 (megawatts-energy) MWe of installed geothermal capacity for power production exist as of December 2019 in Western Anatolia, mostly generated in the BMG. While the BMG is a vastly producing geothermal resource, it is predicted that it has higher production potential. However, other studies do not include field scale 3D geologic models or geothermal gradient maps. This study aims to first quantitatively test the geothermal gradients in the Aydın-İncirliova-Osmanbükü Geothermal Field (IGF), then map the information. This study also aims to compare the IGF with a neighboring geothermal field. To complete this study, information from stratigraphic columns, bottom hole temperatures, and continuous temperature logs from 13 geothermal wells is utilized with Leapfrog Geothermal to create 3D models of the geology and subsurface temperature distribution. Then, isothermal contour maps of the field are created. The geologic modeling suggests that synextensional deposition has occurred within the graben. The temperature modeling suggests both that thermal breakthrough may have occurred in the field, and that the IGF has a higher geothermal gradient than the nearby Germencik Geothermal Field

Surface Heat Flow, Deep Formation Temperature, and Lithospheric Thickness of the Different Tectonic Units in Tarim Basin, Western China

Abstract Herein, the new collected well-testing temperature as well as continuous steady-state temperature logs were achieved for the analysis of deep thermal structural characteristics and current thermal states of various tectonic units in Tarim Basin. Generally, geothermal gradient fluctuates in 14.6-31.1°C/km, the heat flow ranges between 31.6 and 59.2 mW/m2 with the average heat flow of 43.2 mW/m2, and these values are typical of low heat flow background in Precambrian craton basins. Furthermore, estimated formation temperature spatial distributions at 6~8 km depth are the same and are mainly under the control of basement structural pattern. At 6000 m depth, temperature is 99-188°C, which become 126-242°C and 113-215°C at 7000 m and 8000 m depths, respectively. These findings confirmed that heat flow in Tarim Basin was relatively low with similar geothermal regimes to other Precambrian craton basins around the globe. In addition, 1D theoretical crustal thermal structures in Tarim Basin were established based on the solution of the equation of steady-state heat conduction. The findings revealed that “thermal” lithosphere maximum thickness in Tarim Basin is witnessed in Manjiaer sag. Tazhong uplift thermal state differs from those of Tabei uplift and Manjiaer sag. Tazhong mantle heat flow is 23.9 mW/m2, which accounts for 48.8% of surface heat flow. Hotter thermal states of Tazhong uplift generated temperatures as high as ∼690°C in Moho. Tarim Basin heat flow distribution reveals that crustal heat flow plays a more significant role in surface heat flow and possesses typical “hot crust and cold mantle” model thermal structure properties.

Terrestrial heat flow of Jizhong depression, China, Western Bohai Bay basin and its influencing factors

The Jizhong depression in the western Bohai Bay Basin has a high thermal state. Heat flow is one of the most important parameters in geothermics, its measurement can help obtain a better understanding of the regional lithospheric thermal structure. In this study, continuous steady-state temperature logs were obtained from 14 deep boreholes. 136 core samples were measured for thermal conductivity and radiogenic heat production. The temperature data indicated that heat transfer within the sedimentary layer was dominated by heat conduction, with a geothermal gradient of approximately 31.5 ℃•km−1. The gradient value was almost 0 ℃•km−1 in the dolomite strata, due to their abnormally high thermal conductivity and permeability. Average thermal conductivity values was 2.46, 5.51 and 3.21 W•m−1•K−1, and the radiogenic heat production were 1.05, 0.26, and 0.74 μW•m−3 for the sandstone, dolomite and metamorphic rocks, respectively. Higher heat flow in the Jizhong depression is mainly distributed around the subsurface structure of sub-uplift region, which is near the fault between the sub-uplift region and the sub-depression region, and the value can reach 120.0 mW•m−2. With an increase in the dolomite buried depths or an increase in the overlying sandstone thickness, the surface heat flow value decreases. Finally, we discuss the factors influencing the shallow temperature: the lateral sediment thickness variations can markedly influence the temperature distribution. The influence of magma activity that happened long ago can be neglected.

Estimation of Geothermal Gradient, Geothermal Heat Flux and Thermal Conductivity of Rocks in Western Niger Delta Using Well Log Data

This study presents the result of the estimation of heat flow from six (6) wells (Well X:001 to 006) in South-Western Niger Delta using values of Geothermal gradient (GG), Geothermal heat flux (Q) and thermal conductivity (K) computed from Sonic and continuous temperature log data for each well. Geothermal gradient was computed from continuous temperature logs using the simple gradient method while geothermal heat flux and thermal conductivity of the rocks in the wells were computed from the sonic log data, using the Relative Heat Flow Model and Fourier One-dimensional Heat Flow Law respectively. The results were analysed and interpreted to investigate the thermal structure and pattern of heat flow distribution of the basin. Results showed that geothermal gradient ranges from 1.45 0 C/100m to a value of 1.61 0 C/100m, with a simple average of 1.55 0 C/100m. Geothermal gradient contour map computed from this result, showed a low thermal gradient at the northern part of the study area where we have Well X-006 and increases outwards in all direction as we move further offshore. These differences reflect changes in thermal conductivity of rocks, ground water movement and endothermic reaction during diagenesis, since geothermal gradient is influenced by lithology or differential rate of sedimentation. Therefore, it was inferred that sediments with a relatively high geothermal gradient (1.55 to 1.61 0 C/100m) will mature earlier (low oil window) than those with low thermal gradient values. By implication, a high geothermal gradient enhances the early formation of oil at relatively shallow burial depths, but causes the depth range of the oil window to be narrow, while low geothermal gradient causes the first formation of oil to begin at fairly deep subsurface levels, but makes the oil window broad. Geothermal heat flux estimated from subsurface temperature and one-way sound travel time, shows heat flux varying between 33.16 mWm -2 to 72.73 mWm -2 with a simple average of 48.43 mWm -2 . Low heat flux was observed at the central part of the study area which increases towards the western and eastern parts of the area with Well X-005 characterized by a higher geothermal heat flux. Therefore, it was inferred that the western and eastern parts of the study area with higher heat flux values may be characterized as zones with maximum sediment thickness and are characterized as having depressions (gravity low) on the geoid which is characteristics of a basin, while the central part of the study area with low heat flux values correspond with zones of minimum sediment thickness. Also, thermal conductivity of rocks in the study area computed directly from heat flux and geothermal gradient results, ranges from 2.28W/m 0 C to 4.76 W/m 0 C with an average of 3.19 W/m 0 C. Thermal conductivity contour map computed from this result, showed low thermal conductivity values observed at the central part of the study area, and increases outwards towards the west and eastern parts. This pattern of thermal conductivity variation suggests probably there exists heavy crude oil at the central part of the study area and lighter crude oil as we move outward in all direction. It was also observed that within each well, thermal conductivity increased with depth and decreased with porosity which may be caused by difference in lithology and fluid content, due to the fact that all pore fillers (i:e gases and liquids) are poor conductors. The estimated values of geothermal gradient, heat flux and thermal conductivity obtained in this study are similar to the results obtained from previous studies in the region and with other passive continental margins of the world. Keywords: Heat flow, Geothermal Gradient, Geothermal Heat Flux, Thermal Conductivity, Continuous Temperature and Sonic log. DOI: 10.7176/JETP/10-2-04 Publication date: April 30 th 2020

Terrestrial heat flow in the baiyinchagan sag, erlian Basin, northern China

The Baiyinchagan Sag of the Erlian Basin is a Mesozoic continental rift basin located in the eastern part of the Central Asian Orogenic Belt between the North China Craton and the Siberian Craton. The sedimentary fill comprises mainly the Cretaceous sandstones and mudstones underlying Cenozoic succession. Knowledge regarding the factors affecting the tectonic evolution of the Baiyinchagan Sag is lacking. The objective of this study is to obtain new terrestrial heat flow measurements in the Baiyinchagan Sag for constraints on its thermotectonic history. We obtained continuous temperature logs from three boreholes, namely Xi24, Xi3-76 and Xi30 with depths of 1230, 1660 and 2160 m, respectively. Additionally, we gauged the thermal conductivity of the lithologic samples of the main sedimentary rocks. Our analysis indicates that subsurface temperatures are affected by the convection of groundwater and subsurface warming. After removing the influence of groundwater and climatic effects, the subsurface temperature gradients of the Cretaceous Duhongmu and Tenggeer Formations range from 40.4 to 42.1 ℃ km−1. We performed water saturation correction for the measured thermal conductivity data. The thermal conductivities of the Saihantala, the Duhongmu, the Tenggeer, and the Aershan Formations were found to be 1.15, 2.13, 1.99, and 2.15 W m-1 K−1, respectively. Vertical Peclet number analysis of the temperature-depth profile of Xi3-76 borehole with a Peclet number of 0.16 indicates that the conductive heat transfer dominates in the component of the vertical heat transfer. The three new heat flow values range from 80.8 to 89.7 mW m-2, with a mean of 84.9 ± 3.4 mW m-2, significantly higher than the global and regional average whereas consistent with its deep thermotectonic regime.

Terrestrial heat flow and crustal thermal structure in the northern slope of Tazhong uplift in Tarim Basin

Considerable breakthroughs have been obtained recently in deep and ultra-deep carbonate strata of the northern slope of Tazhong uplift, which is characterized by a burial depth of more than 6300 m and is characterized by high burial temperature. However, the lack of systematic temperature research and effective temperature prediction for the ultra-deep strata in northern slope of the Tazhong has seriously restricted the petroleum exploration in the future. The continuous steady-state temperature logs and well test temperature were obtained, and the thermal conductivity were measured to analyze the current thermal state and deep thermal structure characteristics of the northern slope of Tazhong uplift. The geothermal gradient is generally between 19.4 and 28.5 ℃/km, and the geothermal heat flow is 34.3–59.2 mW/m2 with an average of 45.4 mW/m2, which is typical of low heat flow background of the Precambrian craton basin. In addition, the spatial distributions of the estimated formation temperature at the depth of 6˜8 km are also similar and are mainly controlled by the basement structural pattern. The temperature at the depth of 6000 m is 118˜172 ℃, the temperature at 7000 m is 136˜198 ℃, and the temperature at 8000 m is 190˜224 ℃. The temperature gradually increases from Shunbei to Shunnan area, but the temperature near SN4 fault zone is about 10˜20 °C higher than the surrounding rock. This thermal disturbances is possibly caused by hydrothermal fluids passing through the fracture system from the deep strata to the Ordovician strata, with hot alkaline brine from the Lower Cambrian providing heat source, and fault activities providing power and acting as channels for fluids upwelling. Furthermore, the 1-D theoretical crustal thermal structures of the Shunbei and Shunnan area were constructed by solving steady-state heat conduction equation. The results show that the thickness of the “thermal” lithosphere and the Moho temperature in Shunbei area are 177 km and 580 °C, respectively. However, the thickness of the “thermal” lithosphere in Shunnan area is relatively thin, with an average of 149 km. The heat flow distribution on the northern slope of Tazhong indicates the crustal heat flow contributes more to the surface heat flow and has the typical thermal structure characteristics of “hot crust and cold mantle” model.

Greenhouse energy management: The thermal interaction of greenhouses with the ground

Abstract Agriculture is one of mankind's most ecologically impactful activities, representing 70% of society's water usage and 13% of greenhouse gas emissions along with direct impacts on ecologies through land usage, habitat destruction and fertilizer runoff. Global population and per capita demand for food are both growing steadily, so it can be expected that agriculture's ecological impacts will continue to escalate rapidly. Intensive farming techniques are needed, not only to increase crop production but also to manage ecological damage. Greenhouse temperature is instrumental in determining crop yields and water usage, while active ventilation has been shown to contribute significantly to evaporative water losses. It follows that passive methods of greenhouse temperature management are crucial to affordable and efficient agriculture, particularly in developing nations. This research uses continuous temperature logging in small experimental greenhouse units to better understand their thermal interaction with the ground and to evaluate possible modifications in terms of their thermal effects. It is found that partial burying of greenhouses is an effective means of temperature stabilization in hot climates. The analysis showed energy savings of up to 13% and water savings up to 8% are possible, with a payback period of less than a month. This demonstrates that partial burying is both environmentally and financially favourable.

Terrestrial heat flow and crustal thermal structure of the Gonghe-Guide area, northeastern Qinghai-Tibetan plateau

The Gonghe-Guide area, which is located at the northeastern edge of the Qinghai-Tibetan Plateau, has the greatest hot dry rock (HDR) geothermal resources exploration and development potential in China. Separated by the Waligong tectonomagmatic belt, the study area includes the Gonghe and Guide basins, which are characterized by distinctly different thermal state and surface thermal manifestations. Although a number of geophysical explorations have been undertaken, studies on fundamental geothermal theory remain scarce, including a lack of high-quality heat flow determinations and thermal structure studies. In this study, we obtained continuous steady-state temperature logs from three deep boreholes (GR2 and DR3 in the Gonghe basin and ZR1 in the Guide basin). The thermal conductivities and radiogenic heat production rates of the outcrop samples gathered from the two basins were measured. The heat-flow values were determined to be 116.3–122.3mWm−2 for the Gonghe basin, yielding a mean of 119.3mWm−2. Two existed heat flow sites (R2 and R3 boreholes) gave an average heat flow of 75mWm−2 for the Guide basin, which is approximately that of the regional background heat flow level of the northeastern Tibetan Plateau. The 1-D theoretical crustal thermal structures of the Gonghe and Guide basins were constructed by solving steady-state heat conduction equation. The results show that the Moho temperature and mantle heat flow in the Guide basin were 1016°C and 27mWm−2, respectively. However, the temperature field in the Gonghe basin indicated partial melting in the crust. The high temperatures and thus heat flow in the Gonghe basin may suggest the existence of anomalous heat source body in crust. Successful inversions of vertical and horizontal temperature variations of boreholes in the Gonghe basin were obtained by numerically simulating a cooling rectangular magma chamber with a buried depth of 5–6km and horizontal dimensions of 12–14km. The study emphasizes that the anomalous heat flow in the Gonghe basin may be the joint thermal effect of: (1) the high regional background heat flow level of the northeastern Tibetan Plateau, which is mainly due to the radiogenic heat of thickened crust; (2) the cooling of a shallow magma chamber, which may be caused by the uplift and denudation of the plateau.

Improving the temperature predictions of subsurface thermal models by using high-quality input data. Part 2: A case study from the Danish-German border region

We present a 3D numerical crustal temperature model and analyse the present-day conductive thermal field of the Danish-German border region. The model region covers the northernmost part of the North German Basin, a transition zone between the deep-reaching sedimentary rocks of the Glückstadt Graben (including complex salt structures) and the shallow crystalline basement of the Ringkøbing-Fyn High. The modelling approach is novel as it implements for the first time a comprehensive analysis of well-log data on a regional modelling scale. Those logs were used both to derive the spatial distribution of rock thermal conductivity across the study area, and to calculate heat flow values. New values of terrestrial surface heat flow are reported for eight deep boreholes in the North German Basin ranging from 72 to 84mW/m2 with a mean of 80±5mW/m2. The values are computed from continuous temperature logs, carefully corrected BHT values, drill-stem tests and well-log derived rock thermal properties (thermal conductivity, radiogenic heat production) and were included in the setup of the numerical lower boundary conditions. New surface heat flow is up to 20mW/m2 higher than low values reported in some previous studies for this region. Heat flow from the mantle is 33–40mW/m2.The model temperature predictions are validated against 59 temperature observations from 24 wells. The prediction uncertainties between observed and modelled temperatures at deep borehole sites are small (rms=3.5°C, ame=2.1°C). Pronounced lateral temperature variations are predicted and found to be caused mainly by complex geological structures, including a large amount of salt structures and marked lateral variations in the thickness of basin sediments. The associated variations in rock thermal conductivity generate significant variations in model heat flow and large variations in temperature gradients.With regard to the utilization of geothermal energy, the Rhaetian and the Middle Buntsandstein sandstone reservoirs are found with temperatures within the range of 40–80°C, suitable for low enthalpy heating purposes, in most of the area and locally also with higher temperatures. Temperatures above 120°C, of interest for the production of electricity, are observed only in the very southeastern part of the study area.

Development and Characterization of a Continuous Tympanic Temperature Logging (CTTL) Probe for Bovine Animals

<abstract> Developing a research tool that is low cost, easy to install, and can be implemented in group-housed animals is important to quantify parameters needed to promptly assess animal health and well-being. However, a practical and cost-effective solution for monitoring large numbers of animals in a production setting has not been developed. The objectives of this study were to (1) develop a self-contained and easily deployed continuous tympanic temperature logging (CTTL) probe capable of recording and storing tympanic temperature (T_T) data from group-housed beef cattle, (2) determine the minimum sampling interval needed to measure T_T in beef cattle, and (3) quantify the temperature differences among the ears (left and right) and vagina (T_V). A two-part device was developed consisting of a temperature logger housed in a molded foam probe. The CTTL probe can be effectively used to measure T_T in both the left and right ears of group-housed animals. The CTTL is cheaper, faster, and easier to install and remove when compared to past methods. Recovery rate was greatly affected by cattle behavior, weather, duration of collection, and installer, but a recovery rate of ≥75% should be considered successful and ≤50% unsatisfactory. When planning research trials, increasing the number of required animals would compensate for a few dislodged temperature loggers. Periodogram analysis determined that a minimum effective sampling interval of 2.5 min (lower than in past studies) was needed to capture the dynamic nature of T_T in field conditions. Mean temperatures were different (p < 0.0001): 39.3°C, 38.5°C, and 38.4°C for T_V and T_T in the right and left ears, respectively. The mean temperature difference between the ears (left - right = -0.10°C) was smaller than the mean difference between the vagina and each ear (vagina - left ear = 0.92°C; vagina - right ear = 0.83°C). The variability in the temperature profiles both within and between animals presents difficulty in characterizing, modeling, and subsequent prediction of thermal status using mean values. Future research should be directed toward characterizing T_T profiles of beef cattle using signal analysis for different phenotypes and growth stages.

High-quality heat flow determination from the crystalline basement of the south-east margin of North China Craton

Very few of heat flow data have come from the crystalline basement in the North China Craton but rather from boreholes in the sedimentary cover of oil–gas basins. Explorations for hot dry rock (HDR) geothermal resources and porphyry gold deposits in eastern China offer now valuable opportunities to study the terrestrial heat flow in the crystalline basement. In this study, we obtained continuous temperature logs from two boreholes (the LZ borehole with a depth of 3471m and the DR borehole with a depth of 2179m) located in the south-east margin of the North China Craton. The boreholes have experienced long shut-in times (442days and 261days for the LZ borehole and DR borehole, respectively); thus, it can be expected that the temperature conditions have re-equilibrated after drilling and drill-mud circulation. Rock thermal conductivity and radiogenic heat production were measured for 68 crystalline rock samples from these two boreholes. The measured heat-flow density was determined to be 71.8±2.3mWm−2 (for the LZ borehole) and 91.5±1.2mWm−2 (for the DR borehole). The heat flow for the LZ borehole is close to the value of 75mWm−2 determined in the Chinese Continental Scientific Drilling main hole (CCSD MH), both being in the Sulu-Dabie orogenic belt and thus able to verify each other. The value for the DR borehole is higher than the above two values, which supports former high heat-flow values determined in the Bohai Bay Basin.

Thermal conditions of the central Sinai Microplate inferred from new surface heat-flow values and continuous borehole temperature logging in central and southern Israel

This paper reports ten new surface heat-flow density (qs) values for central and southern Israel (central Sinai Microplate), whose crystalline crust and lithosphere formed as part of the Neoproterozoic Arabian-Nubian Shield. Heat flow was calculated in Mesozoic sediments using the classical approach of heat-flow determination by implementing in the analysis high-precision continuous temperature logs obtained in air- and/or water-filled boreholes. Thermal conductivity (TC) measured for a large suite of rock samples of lithotypes making up the sequence was assigned to temperature gradients in intervals for which the lithology was known. The heat-flow values obtained for different depth intervals in a borehole as well as the average values for the individual borehole locations cover a narrow range, attesting heat-conduction conditions. A steady-state thermal model along an E–W crustal cross section through the area shows that the observed systematic spatial distribution of the qs values, which range between 50 and 62mWm−2, can primarily be explained by variations in the thickness of the upper crust and in the ratio between sedimentary and crystalline rocks therein. Given the time lapse of thermal heat transfer through the lithosphere, the qs data monitor the crustal thermal conditions prior to rift- and plume-related lithospheric thermal perturbations that have started in the larger area ca. 30Ma ago. Observed and modeled qs display the best fit for a pre-Oligocene lithosphere–asthenosphere boundary (LAB) at ∼150km, which would be at the upper end of LAB depths determined from stable areas of the Arabian Shield (150–120km) not affected by the young, deep-seated thermal processes that have caused a further uprise of the LAB. Our data imply or predict that the surface heat flow of the Sinai Microplate generally tends to increase along N–S and W–E traverses, from ∼45–50mWm−2 to ∼55–60mWm−2. Surface heat flows on the order of 55–60mWm−2 may be common in the northern Arabian Shield, where it exhibits typical lithosphere structure and composition and is unaffected by young heating processes, compared to values of ≤45mWm−2 recently determined in the southern Arabian Plate for the Arabian Platform.

Heat flow and lithospheric thermal regime in the Northeast German Basin

New values of surface heat flow are reported for 13 deep borehole locations in the Northeast German Basin (NEGB) ranging from 68 to 91 mW m − 2 with a mean of 77 ± 3 mW m − 2 . The values are derived from continuous temperature logs, measured thermal conductivity, and log-derived radiogenic heat production. The heat-flow values are supposed free of effects from surface palaeoclimatic temperature variations, from regional as well as local fluid flow and from thermal refraction in the vicinity of salt structures and thus represent unperturbed crustal heat flow. Two-D numerical lithospheric thermal models are developed for a 500 km section along the DEKORP-BASIN 9601 deep seismic line across the basin with a north-eastward extension across the Tornquist Zone. A detailed conceptual model of crustal structure and composition, thermal conductivity, and heat production distribution is developed. Different boundary conditions for the thickness of thermal lithosphere were used to fit surface heat flow. The best fit is achieved with a thickness of thermal lithosphere of about 75 km beneath the NEGB. This estimate is corroborated by seismological studies and somewhat less than typical for stabilized Phanerozoic lithosphere. Modelled Moho temperatures in the basin are about 800 °C; heat flow from the mantle is about 35 to 40 mW m − 2 . In the southernmost part of the section, beneath the Harz Mountains, higher Moho temperatures up to 900 to 1000 °C are shown. While the relatively high level of surface heat flow in the NEGB obviously is of longer wave length and related to lithosphere thickness, changes in crustal structure and composition are responsible for short-wave-length anomalies.

In-situ thermal conductivity estimates in the Western Niger Delta sediments derived from geophysical logs.

An estimate of thermal conductivity was carried out in 21 well-spaced petroleum wells in the western Niger Delta using sonic and continuous temperature logs. The temperature logs were measured after the wells had attained thermal equilibrium as a result of drilling activities. Regional thermal conductivity varies from 1.1Wm-1 0C-1 to 6.2 Wm-1 0C-1, with an average of 3.1Wm-1 0C-1. The North-Central part of the studied area is characterized by high thermal conductivity and this decreases towards the North-East and seawards. The values are lowest around the sea with an average of 1.43Wm-1 0C-1. Our method of direct computation is in agreement with previous works and are also comparable to those of other passive continental margins in the world. Journal of the Nigerian Association of Mathematical Physics Vol. 9 2005: pp. 425-430

The surface heat flow of the Arabian Shield in Jordan

Surface heat flow in southern Jordan (western part of the Arabian Plate) was determined in a dense cluster of five, up to 900-m-deep boreholes that have encountered sedimentary rocks of Paleozoic (Ordovician and Silurian) age. These rocks are underlain by an igneous and metamorphic basement, which has been studied for its radiogenic heat production, along the eastern margin of the Dead Sea Transform (DST) fault system. The heat flow, calculated from continuous temperature logs and laboratory-measured thermal conductivity of drillcores and surface samples, averages to 60.3 ± 3.4 mW m −2 and contrasts the common view of the late Proterozoic-consolidated Arabian Shield constituting a low heat-flow province of ⩽45 mW m −2. Although only characterizing an area of about 300 km 2, this average is unlikely representing a positive local anomaly caused by voluminous HHP granites/rhyolites at shallow depths. Instead, a heat flow of 60 mW m −2 is considered a robust estimate of the Phanerozoic conductive surface heat flow not only for Jordan, but for the Arabian Shield in areas unaffected by younger reactivation. The large variation in conductive heat flow (36–88 mW m −2) previously observed in Jordan, southern Syria, and Saudi Arabia is irreconcilable with their broad similarity in lithosphere structure and composition and rather reflects a combination of factors including low-quality temperature data and insufficient knowledge on thermal rock properties.

Temperature changes in Poland from the 16th to the 20th centuries

A standardized tree-ring width chronology of the Scots pine (Pinus sylvestris L.) along with different types of documentary evidence (e.g. annals, chronicles, diaries, private correspondence, records of public administration, early newspapers) have been used to reconstruct air temperature in Poland. The ground surface temperature (GST) history has been reconstructed based on the continuous temperature logs from 13 wells, using a new method developed recently by Harris and Chapman (1998; Journal of Geophysical Research103: 7371–7383) which is compared with the functional space inversion (FSI) method applied to all available Polish temperature–depth profiles analysed before. Response function calculations conducted for trees growing in Poland (except in mountainous regions) reveal a statistically significant correlation between the annual ring widths of the Scots pine and the monthly mean air temperatures, particularly from February and March, but also from January and April. Therefore, it was only possible to reconstruct the mean January–April air temperature. The following periods featured a warm late winter/early spring: 1530–90, 1656–70 (the warmest period), 1820–50, 1910–40, and after 1985. On the other hand, a cold January–April occurred in the following periods: 1600–50, 1760–75, 1800–15, 1880–1900, and 1950–80. Reconstructions of thermal conditions using documentary evidence were carried out for winter (December–February) and summer (June–August) from 1501 to 1840 and, therefore, their results cannot be directly compared with reconstructions based on tree-ring widths. Winter temperatures in this period were colder than air temperature in the 20th century. On the other hand, ‘historical’ summers were generally warmer than those occurring in the 20th century. Such situations dominated in the 16th and 17th centuries, as well as at the turn of the 18th and 19th centuries. Throughout almost the entire period from 1501 to 1840, the thermal continentality of the climate in Poland was greater than in the 20th century. GST reconstructions show that its average pre-instrumental level (1500–1778) is about 0.9–1.5 °C lower than the mean air temperature for the period 1951–81. Lower amplitude of GST warming (0.9 ± 0.1 °C) results from the individual and simultaneous inversions of well temperature data using the FSI method. A very good correspondence of the results has been found between series of annual mean GSTs from the FSI method and mean seasonal air temperatures reconstructed using documentary evidence. Copyright © 2005 Royal Meteorological Society

Continuous Temperature Logging in Air across the Deep Vadose Zone

Accurate temperature measurements with good depth resolution will be helpful in appreciating processes that influence temperatures in the vadose zone. In some areas, such as the Albuquerque Basin, groundwater flow perturbs the temperature regime in the saturated zone, making the deep vadose zone a potentially better region to investigate ground surface temperature changes. When it is not logistically or economically possible to span the vadose zone with a pipe filled with water, the temperature measurements must be made in air. Because of the very small heat capacity of air, these temperature measurements are difficult. This paper describes a new temperature sensor with a relatively fast time constant in air that provides accurate temperature measurements in a continuous logging mode. Temperature gradient characteristics below the 5-m depth, based on a 1-m depth measurement interval, are reproducible at a number of logging speeds. Absolute temperatures between the logs at any given depth below about 25 m typically agree to within 0.01°C. The temperature logging system should enable one to gather considerable information regarding the thermal regime in the vadose zone.

Continuous Temperature Logging in Air across the Deep Vadose Zone

Accurate temperature measurements with good depth resolution will be helpful in appreciating processes that influence temperatures in the vadose zone. In some areas, such as the Albuquerque Basin, groundwater flow perturbs the temperature regime in the saturated zone, making the deep vadose zone a potentially better region to investigate ground surface temperature changes. When it is not logistically or economically possible to span the vadose zone with a pipe filled with water, the temperature measurements must be made in air. Because of the very small heat capacity of air, these temperature measurements are difficult. This paper describes a new temperature sensor with a relatively fast time constant in air that provides accurate temperature measurements in a continuous logging mode. Temperature gradient characteristics below the 5‐m depth, based on a 1‐m depth measurement interval, are reproducible at a number of logging speeds. Absolute temperatures between the logs at any given depth below about 25 m typically agree to within 0.01°C. The temperature logging system should enable one to gather considerable information regarding the thermal regime in the vadose zone.

Geothermal gradients in the Niger Delta basin from continuous temperature logs

Subsurface temperatures obtained from continuous temperature logs in 260 wells allowed to stabilize for several months were used in determining the geothermal gradients in the Niger Delta. Regional gradients are lowest (0.82oC/100m) at the central part of the Delta and increases both seaward and northward up to 2.62oC/100m and 2.95oC/100m respectively in the continental sands of the Benin formation. In the marine paralic deposition, geothermal gradients range from 1.83oC/100m to 3.0oC/100m at the central portions. The highest values of 3.5oC/100m to 4.6oC/100m are seen northwards while intermediate values of 2.0oC/100m to 2.5oC/100m are recorded seaward. The thermal gradients are clearly influenced by the lithology or rate of sedimentation in the area. Regions of low thermal gradients correspond with areas of high sand percentage, primarily because sands are better conductors than shale and therefore show as low thermal gradients. There is a continuous but non-linear relationship between geothermal gradients and depth, from less than 1.0oC/100m in the continental sands through 2.5oC/100m in the marine paralic section to 5.0oC/100m in the continuous shaly section. Key words: Geothermal gradient, temperature, sand percentage, heat flow (Global Journal of Pure and Applied Sciences: 2003 9(2): 265-272)