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Understanding the thermal behavior of nonsteady state subsurface geosystems, when temperature changes over time, requires knowledge on the speed of heat propagation and, thus, of the rock's thermal diffusivity as essential thermo-physical parameter. Mixing models are commonly used to describe thermo-physical properties of polymineralic rocks. A thermal diffusivity-porosity relation is known from literature that incorporates common mixing models into the heat equation and properly works for unconsolidated, clastic clayey, and sandy marine sediments of high porosity (35%–80%). We have proofed the relation's applicability for consolidated, isotropic sedimentary rocks of low porosity (

The GeoTief EXPLORE project aims to explore the geothermal potential and quantify the geothermal resources of the Vienna Basin (Austria) and the underlying Northern Calcareous Alpine basement. The main target of geothermal interest is the massive and tectonically remolded Hauptdolomite facies that has been identified as potential geothermal reservoir in previous studies. Now, this formation is studied using outcrop analogues for the investigation of their petrophysical characterization and specific thermal properties (thermal conductivity and thermal diffusivity). Here, we report new measurements on a total of 60 samples from 6 outcrops in and around the area of Vienna applying different methods for the laboratory measurement of thermal and hydraulic rock properties. The petrophysical analysis considers the impact of deformation along and across fault zones, which introduces heterogeneity of storage properties and consequently in the thermophysical properties. Using the standard fault core and damage zone model, outcrop samples were grouped into unfractured and fractured protoliths, as well as in fault rocks, like breccias and cataclasites. Rock samples are then classified by their fracture density (m² fracture surface per m³ rock) and by their matrix content and differences in grain sizes, respectively. The measured thermal rock properties vary significantly between the selected rock groups. The total range [90 % of values] is between 3.2 and 5.0 W/(mK) for thermal conductivity and between 1.3 and 2.7 mm²/s for thermal diffusivity. The results generally met the expected trend for fractured rocks as conductivity and diffusivity decreases with increasing porosity under unsaturated and saturated conditions. The total porosities are less than 5%. The variability of thermal conductivity under saturated conditions shows complex trends depending on the different rock classifications where fault rocks and highly fractured rocks of the damage zone show lower increase in thermal conductivities. The new petrophysical characterization will be the base for further numerical investigations of the hydraulic and thermal regime as well as for the analysis of the geothermal resources of the Hauptdolomite.

Precise knowledge of the subsurface thermal field plays a key role in the assessment of geothermal targets. Unfortunately, deep underground temperature data is generally scarce and a matter of research. To achieve first estimates for subsurface temperatures, steady-state conductive thermal modeling is commonly applied. Thereby the rock thermal conductivity is an essential parameter, which is usually determined under ambient laboratory conditions. To arrive with in situ thermal conductivity, the ambient values need to be corrected for in situ temperature and pressure. In this paper, we apply different conversion functions for the correction of thermal conductivity and study the impact on the resultant temperature and heat flow prognoses for a synthetic, upper crustal sedimentary and a magmatic scenario along 2-D geological cross sections. Application of the correction functions results in maximum temperature prognosis uncertainties of about 8 °C and 55 °C at 2 km depth and at 8 km depth, respectively. The effect positively correlates with the magnitude of the basal heat flow used in modeling. In contrast to the heat flow determined at depth, the resulting surface heat flow is only minor affected by the different correction functions applied. In addition, the modeled temperature at depth is strongly dependent on the type and sequence of application of the pressure and temperature correction equations.

The paper addresses the effects of pressure (P) and temperature (T) on thermal conductivity (λ) applied to crustal geotherms. A subset of the ca. 50 experimentally derived numerical P―T relations available in literature for typical crustal rock types was selected for this purpose. The relations comprise those from physical-contact laboratory methods (PCM), for P and T, as well as from a non-contact technique, the laser-flash analysis (LFA), for T. The effects on geotherms are quantified for two crustal models: (I) a simplified two-layer “Proterozoic” crust, which consists of granitic rocks in the upper part and granulitic rocks in the lower part and (II) a multi-layer “Phanerozoic” crust. We show that neglecting P–T correction of ambient λ leads to underestimation of T that is larger with increasing surface heat flow (qs). In the Phanerozoic crust, the T difference at the crust–mantle boundary is 130/50 K [PCM/LFA], for qs 60 mW m–2, and 240/100 K, for qs 80 mW m–2. In the Proterozoic crust, with qs typically

In this study, equations are developed that predict for synthetic sedimentary rocks (clastics, carbonates, and evaporates) thermal properties comprising thermal conductivity, specific heat capacity, and thermal diffusivity. The rock groups are composed of mineral assemblages with variable contents of 15 major rock-forming minerals and porosities of 0 – 30 per cent. Petrophysical properties and their well-logging-tool-characteristic readings were assigned to these rock-forming minerals and to pore-filling fluids. Relationships are explored between each thermal property and other petrophysical properties (density, sonic interval transit time, hydrogen index, volume fraction of shale, and photoelectric absorption index) using multivariate statistics. The application of these relations allows computing continuous borehole profiles for each rock thermal property. The uncertainties in the prediction of each property vary depending on the selected well-log combination. Best prediction is in the range of 2–8 per cent for the specific heat capacity, of 5–10 per cent for the thermal conductivity, and of 8–15 for the thermal diffusivity, respectively. Well-log derived thermal conductivity is validated by laboratory data measured on cores from deep boreholes of the Danish Basin, the North German Basin, and the Molasse Basin. Additional validation of thermal conductivity was performed by comparing predicted and measured temperature logs. The maximum deviation between these logs is

Comprehensive knowledge of surface heat flow and subsurface temperature distribution is indispensable for the interpretation and quantification of crustal/mantle processes as well as for the evaluation of the geothermal potential of an area. In cases where subsurface temperature data are sparse, thermal modeling may be used as a tool for inferring the geothermal resource at depth but requires profound structural, geological, and petrophysical input data. The study area encompasses the Trier–Luxembourg Basin and the western realm of the Rhenish Massif, itself subdivided into the Ardennes region in the west as well as the Eifel and Hunsruck regions in the east. For the study area, 2-D steady-state and conductive thermal models were established based on geological models of lithosphere-scale which were parameterized using thermal rock properties including thermal conductivity, radiogenic heat production, and density. The thermal models are constrained by surface heat flow (qs) and the geophysically-estimated depth of the lithosphere–asthenosphere boundary (LAB). A qs of 75 ± 7 (2σ) mW m−2 was determined in the area. A LAB depth of 100 km, as seismically derived for the Ardennes, provides the best fit with the measured qs. Modeled temperatures are in the range of 120–125 °C at 5 km depth and of 600–650 °C at the Moho, respectively. The mantle heat flow amounts to ∼40 mW m−2. Possible thermal consequences of the 10–20 Ma old Eifel plume, which caused elevation of the LAB to 50–60 km depth, were modeled in a steady-state thermal scenario resulting in a qs of 91 mW m−2 in the Eifel region. Available qs values (65–80 mW m−2) are significantly lower and do indicate that the plume-related heating has not yet reached the surface in its entirety.

Thermal conductivity (lambda) is an essential physical property of minerals and rocks and fundamental in constraining the thermal field of the lithosphere. In case that adequate samples to measure lambda are not available, it could be indirectly inferred from calculation. One of the most widely applied indirect methods for rocks involve modal mineralogy and porosity as parameters that are incorporated into mathematical mean or mixing models. Robust inferences from these approaches for crystalline rocks were impeded by a small number of studied samples or restriction to certain rock types. We employ this method and examine its applicability to low-porosity plutonic rocks by calculating bulk thermal conductivity lambda(b) for 45 samples covering the entire range from gabbro/diorite to granite. We show that the use of the harmonic-mean model for both rock matrix and porosity provided a good match between lambda(b.meas) and lambda(b.calc) of

This paper addresses aspects of a baseline geothermal exploration of the thermally quiescent Elbe Zone (hosting the cities of Meissen and Dresden) for a potential deployment of geothermal heat in municipal heating systems. Low-permeable to impermeable igneous and metamorphic rocks constitute the major rock types at depth, implying that an enhanced geothermal system needs to be developed by creating artificial flow paths for fluids to enhance the heat extraction from the subsurface. The study includes the development of geological models for two areas on the basis of which temperature models are generated at upper crustal scale. The models are parameterized with laboratory-measured rock thermal properties (thermal conductivity k, radiogenic heat production H). The uncertainties of modelled temperature caused by observed variations of k and H and inferred mantle heat flow are assessed. The study delineates highest temperatures within the intermediate (monzonite/syenite unit) and mafic rocks (diorite/monzodiorite unit) forming the deeper portions of the Meissen Massif and, specifically for the Dresden area, also within the low-metamorphic rocks (slates/phyllites/quartzites) of the Elbtalschiefergebirge. Boreholes 3–4 km deep need to be drilled to reach the envisioned economically favourable temperatures of 120 °C. The metamorphic and mafic rocks exhibit low concentrations of U and Th, thus being advantageous for a geothermal use. For the monzonite/syenite unit of high heat production (~6 µW m−3) in the Meissen Massif, the mobilization of Th and U into the geothermal working fluid is assumed to be minor, although their various radioactive decay products will be omnipresent during geothermal use.

The joint project CLEAN was a Research & Development (R&D) action accompanying a pilot Enhanced Gas Recovery (EGR) project designed by GDF SUEZ E&P Deutschland GmbH (GDF SUEZ) in cooperation with Vattenfall Europe. Within the framework of this project a total of 16 German research and industry partners participated. The project was set up as pilot to investigate the processes relevant to EGR by the injection of CO2 into a subfield of the almost depleted Altmark natural gas field (Germany). Despite the setback that permission for active injection was not granted by the mining authority during the period of the project, important results fostering the understanding of processes linked with EGR were achieved. The CLEAN results provide the technological, logistic and conceptual prerequisites for implementing a CO2-based EGR project in the Altmark and provide a benchmark for similar projects in the world.

The joint research project CLEAN was conducted in the years 2008–2011 by a German research and development (R&D) alliance of 16 partners from science and industry. The project was set-up as pilot project to investigate the processes relevant to enhanced gas recovery (EGR) by the injection of CO2 into a subfield of the almost depleted Altmark natural gas field. Despite the setback that permission for active injection was not issued by the mining authority during the period of the project, important results fostering the understanding of processes linked with EGR were achieved. Work carried out led to a comprehensive evaluation of the EGR potential of the Altmark field and the Altensalzwedel subfield in particular. The calculated safety margins emphasize that technical well integrity of the 12 examined boreholes is given for EGR without a need for any further intervention. The laboratory and field tests confirm that the Altensalzwedel subfield is suitable for the injection of 100,000 t of CO2. Numerical simulations provide sound predictions for the efficiency and safety of the EGR technology based on the CO2 injection. The development and testing of different monitoring techniques facilitate an improved surveying of CO2 storage sites in general. The CLEAN results provide the technological, logistic and conceptual prerequisites for implementing a CO2-based EGR project in the Altmark and provide a benchmark for similar projects in the world.

This study reports laboratory-measured thermal-conductivity values of Mesozoic sandstones from eight wells (predominantly geothermal boreholes) of the Northeast German Basin (NEGB). The measurements were made on drill core using the optical scanning method. Bulk thermal conductivities of sandstones corrected for in situ thermal conditions range between 2.1 and 3.9 W/m/K. In general, the Mesozoic sandstones show a large effective porosity typically ranging between 16% and 30%. Matrix thermal conductivity ranges from 3.4 to 7.4 W/m/K. The higher values reflect the large quartz content in sandstone. Based on the in situ thermal conductivity and corresponding interval temperature gradient, obtained from high-precision temperature logs measured under thermal borehole equilibrium, interval heat-flow values were computed in the Middle Buntsandstein section (between 1400 and 1500 m) of two boreholes located in the Stralsund area. The heat flow averages to 74 mW/m² (Gt Ss 1/85 borehole) and 78 mW/m² (Gt Ss 2/85 borehole) and, by adding a heat-flow component of 1.8 mW/m² for the heat production in the overburden, are in good correspondence with previously reported surface heat flow of 77 mW/m². Based on these values and the temperature log information, thermal conductivity was indirectly calculated for the entire borehole profiles. The discrepancy between laboratory-measured and computed thermal conductivities in the two boreholes is in the order of 0.24 and 0.56 W/m/K. Formation in situ thermal conductivity of the Mesozoic section ranges between 1.5 and 3.1 W/m/K.

Here we report on the framework of geological site exploration, which encompassed investigations at different scales prior to and after the drilling of the three CO2SINK boreholes. Past and new exploration data are integrated to delineate at regional scale (1) the geological structure of CO2 storage formation and its overburden, including fault systems as potential fluid pathways and (2) the shallow hydrogeology and the groundwater flow directions for an assessment of effects in case of CO2 leakage and migration. The poro-perm facies and mineralogical composition of the CO2 reservoir rock and the top seal formation were studied by routine and special core analyses, including the measurement of porosity, gas and brine permeability, and by XRD analysis.

A 3D 25-fold seismic survey with a bin size of 12 by [Formula: see text] and about [Formula: see text] of subsurface coverage was acquired in 2005 near a former natural gas storage site west of Berlin, as part of the five-year EU funded [Formula: see text] project. Main objectives of the seismic survey were to verify earlier geologic interpretations of structure based on vintage 2D seismic and borehole data and to map, if possible, the reservoir pathways in which the [Formula: see text] will be injected at [Formula: see text] depth, as well as providing a baseline for future seismic surveys and planning of drilling operations. The uppermost [Formula: see text] are well imaged and show an anticlinal structure with an east-west striking central graben on its top that extendsdown to the target horizon. About [Formula: see text] of throwis seen on the bounding faults. No faults are imaged near the planned drill sites. Remnant gas, cushion and residual gas, is present near the top of the anticline in the depth interval of about [Formula: see text] and has a clear seismic signature; both higher amplitudes in the reservoir horizons and velocity pulldown are observed. Amplitude mapping of these remnant gas horizons shows that they do not extend as far south as the injection site, which is located on the southern flank of the anticline. Amplitude anomalies, gas chimneys along an east-west striking fault, show that the stored or remnant gas either has been or is presently migrating out of the reservoir formations. Summed amplitude mapping of the planned injection horizon indicates that this lithologically heterogeneous formation may be more porous at the injection site.

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.

Vorgestellt wurde ein innovatives mathematisches Modell zur Bestimmung der mittelfristigen Produktions- und Ablaufplanung fur eine deutsche Brauerei. Dabei handelt es sich um ein gemischt-ganzzahliges Optimierungsproblem, das durch die Vorgabe von Rustsequenzen gekennzeichnet ist. Ferner greifen wir auf die Reformulierung des Capacitated Lot-Sizing Problem als Standortproblem zuruck. Fur den Praxisfall konnte gezeigt werden, dass unter Verwendung der algebraischen Modellierungssprache GAMS/Cplex mit vertretbarem Rechenaufwand nahezu exakte Losungen bestimmbar sind.

The thermal diffusivity of felsic and intermediate granulites (charnockites, enderbites), mafic granulites, and amphibolite-facies gneisses has been measured up to temperatures of 550 °C using a transient technique. The rock samples are from the Archean and Pan-African terranes of the Southern Indian Granulite Province. Thermal diffusivity at room temperature (DRT) for different rock types ranges between 1.2 and 2.2 mm2 s− 1. For most of the rocks, the effect of radiative heat transfer is observed at temperatures above 450 °C. However, for few enderbites and mafic granulites, radiative heat transfer is negligible up to 550 °C. In the temperature range of conductive heat transfer, i.e., between 20 ° and 450 °C, thermal diffusivity decreases between 35% and 45% with increasing temperature. The temperature dependence of the thermal diffusivity is directly correlated with the thermal diffusivity at room temperature, i.e., the higher the thermal diffusivity at room temperature, DRT, the greater is its temperature dependence. In this temperature range i.e., between 20 and 450 °C, thermal diffusivity can be expressed as D = 0.7 mm2 s−1 + 144 K (DRT − 0.7 mm2 s−1) / (T − 150 K), where T is the absolute temperature in Kelvin. At higher temperatures, an additional radiative contribution is observed according to CT3, where C varies from 10− 9 to 10− 10 depending on intrinsic rock properties (opacity, absorption behavior, grain size, grain boundary, etc). An equation is presented that describes the temperature and pressure dependence thermal diffusivity of rocks based only on the room-temperature thermal diffusivity. Room-temperature thermal diffusivity and its temperature dependence are mainly dependent on the major mineralogy of the rock. Because granulites are important components of the middle and lower continental crust, the results of this study provide important constraints in quantifying more accurately the thermal state of the deeper continental crust.

In this study, the bulk thermal conductivity (TC) of 26 rock samples representing different types of granulite-facies rocks, i.e. felsic, intermediate and mafic granulites, from the Southern Granulite Province, India is measured at dry and saturated conditions with the optical-scanning method. Thermal conductivity also is calculated from modal mineralogy (determined by XRD and EPMA), applying several mixing models commonly used in thermal studies. Most rocks are fine- to medium -grained equigranular in texture. All samples are isotropic to weakly anisotropic and possess low porosities (< 2%). Measured TC values range between 2.5 and 3.0 W m-1 K-1 for felsic granulites, between 2.5 and 3.5 W m-1 K-1 for intermediate granulites and between 2.4 and 2.7 W m-1 K-1 for mafic granulites. Considering this data and literature compilations, rocks representative for the lower continental crust typically display values between 2 and 3 W m-1 K-1 at ambient temperature and pressure conditions. Depending on the mixing model and the mineral TC value used in the calculations, measured and calculated bulk TC could be properly fitted. For mean values of mineral TCs, the harmonic mean provides an almost perfect fit, with a mean deviation of −1 ± 6% (1s). However, the implication of that correspondence would be that minerals and pores are predominantly aligned parallel, which is in apparent contrast to the texture of the rocks studied here. The geometric mean, which does not consider any layering of minerals or pores in the rock and, thus, should be in better harmony with the textural characteristics of the studied high-grade rocks, matches the measured TC data very well, if minimal minerals TCs reported in the literature are applied (mean deviation 5 ± 8%). In case of non-availability of If appropriate samples (in terms of sample size or physical-chemical-mechanical condition) for laboratory measurement are not available, bulk TC of high-grade metamorphic rocks with low anisotropy and porosity could be satisfactorily good assessed from modal mineralogy, using the data sets for mineral TC applied in this study. Further work is required on the applicability of mixing models to compute TC of other rock types, e.g., of igneous and sedimentary rocks.

Temperature recordings from exploration boreholes for hydrocarbons and geothermal energy are evaluated to select the best-suitable data for determining formation temperature and heat flow in the Northeast German Basin. Repeated temperature logs measured in several boreholes allow a classification into equilibrium logs and perturbed logs. For the latter, a simple empirical correction is proposed based on mean annual ground-surface temperature, the estimated amount of temperature correction at total depth of log, and the depth-dependent cross-over point of temperature perturbation due to drilling. Analysis of bottom-hole temperatures (BHTs) showed that the uncorrected values deviate, on average, by as much as 22.2±10.2°C (1σ) from the formation temperature. BHTs corrected using the Horner-plot method are systematically too low by 1–2°C compared to values corrected using the exact solution to the full line-source equation. Both correction methods yield values that underestimate formation temperatures by as much as 9°C and 8°C, respectively. The large standard deviation (1σ) of about ±8°C indicates that a corrected BHT reflects (with 96% confidence, 2σ) formation temperature not better than ±16°C. However, using temperature logs in conjunction with the corrected BHTs allowed a prediction of formation temperatures with an error less than ±10°C at somewhat deeper depths than the log in several boreholes. The availability of continuous temperature logs as a prerequisite for a reduction of error of BHTs significantly reduced the quantity of useable corrected BHTs in the basin.

New and revised heat-flow density determinations for the Central Andes in Chile and Bolivia between 60° and 75°W and between 15° and 30°S are presented. Heat flow was determined from temperature logs obtained from fourteen boreholes in northern Chile and from a large Bottom-Hole Temperature (BHT) data set in Bolivia. Thermal data were corrected for perturbations resulting from drilling, topography, and fluid circulation, and effects of porosity and temperature were considered in adjusting thermal conductivity for in-situ conditions. Thus, the 74 reliable heat-flow values available were used to interpret heat flow in the context of lithospheric conditions. The heat flow in the Andean orogen shows a strong dependence on the different tectono-morphologic units. Clusters of heat-flow values projected onto a W-E profile reflect significant changes from the Nazca Plate in the west to the Chaco Basin in the east. Heat-flow density is low (20 mW/m2) in the area of the Coastal Cordillera and high (50–180 mW/m2) in the active magmatic arc and the Altiplano. The back-arc region is characterized by a comparably high heat flow (80 mW/m2) whereas the Andean foreland has a heat flow of 40 mW/m2, which is slightly lower than the heat flow in the adjacent Brazilian Shield farther east. The Central Andean subduction zone shows a heat-flow pattern similar to the active margin of the North American continent, but differs in the subduction parameters. Consequently, this results in different lithospheric thermal conditions.

Field tests were conducted in the summer of 1995 on four state-of-the-art temperature logging systems: an analog, electric-line, system; two pressure and temperature recording memory tools (in-hole computer systems); and a Distributed optical fibre Temperature Sensing (DTS) system. The tools produced accurate, detailed, temperature versus depth and temperature gradient versus depth logs at depths to 2 km and temperatures to 200°C. Absolute temperature differences up to 0.4°C were noted between tools. The computer and electric-line tools have significantly better precision and resolution than the DTS, but the DTS has the advantage of being able to measure temperature instantaneously throughout the hole, and would be well suited for monitoring dynamic systems and gas-filled wells. The multiple independent logs demonstrate that most of the “noise” seen in gradient logs is due to convection cells, which may have dimensions several times the borehole diameter, and that these convection cells are currently the limiting factor in resolving wellbore temperatures in most settings.

Data on rock thermal conductivity (TC) are important for the quantification of the subsurface temperature regime and for the determination of heat flow. If drill core is not retrieved from boreholes and thus no laboratory measurement of TC can be made, other methods are desired to determine TC. One of these methods is the prediction of TC from well logs. We have examined the relationships between TC and standard well-log data (gamma ray, density, sonic interval transit time, hydrogen index and photoelectric factor) by a theoretical analysis and by using real subsurface data from four boreholes of the North German Basin. The theoretical approach comprised the calculation of TC from well-log response values for artificial sets of mineral assemblages consisting of variable contents of 15 rock-forming minerals typical for sedimentary rocks. The analysis shows different correlation trends between TC and the theoretical well-log response in dependence on the mineral content, affecting the rock matrix TC, and on porosity. The analysis suggests the development of empirical equations for the prediction of matrix TC separately for different groups of sedimentary rocks. The most valuable input parameters are the volume fraction of shale, the matrix hydrogen index and the matrix density. The error of matrix TC prediction is on the order of 4.2 ± 3.2 per cent (carbonates), 7.0 ± 5.6 per cent (evaporites), and 11.4 ± 9.1 per cent (clastic rocks). From the subsurface data, comprising measured TC values (n = 1755) and well-log data, four prediction equations for bulk TC were developed resembling different lithological compositions. The most valuable input parameters for these predictions are the volume fraction of shale, the hydrogen index and the sonic interval transit time. The equations predict TC with an average error between 5.5 ± 4.1 per cent (clean sandstones of low porosity; Middle Buntsandstein), 8.9 ± 5.4 per cent (interbedding of sandstone, silt- and claystones; Wealden), and 9.4 ± 11 per cent (shaly sandstones; Stuttgart Fm.). An equation including all clastic rock data yields an average error of 11 ± 10 per cent. The subsurface data set also was used to validate the prediction equation for matrix TC established for clastic rocks. Comparison of bulk TC, computed from the matrix TC values and well-log porosity according to the geometric-mean model, to measured bulk TC results in an accuracy

Large numbers of bottom-hole temperatures (BHTs) and temperatures measured during drill-stem tests (DSTs) are available in areas explored for hydrocarbons, but their usefulness for estimating geothermal gradients and heat-flow density is limited. We investigated a large data set of BHT and DST measurements taken in boreholes in the American Midcontinent, a geologically uniform stable cratonic area, and propose an empirical correction for BHTs based on relationships between BHTs, DSTs, and thermal logs. This empirical correction is compared with similar approaches determined for other areas. The data were analyzed by multivariate statistics prior to the BHT correction to identify anomalous measurements and quantify external influences. Spatial patterns in temperature measurements for major stratigraphic units outline relations to regional structure. Comparision of temperature and structure trend-surface residuals reveals a relationship between temperature highs and local structure highs. The anticlines, developed by continuous but intermittent movement of basement fault blocks in the Late Paleozoic, are subtle features having closures of 10–30 m and contain relatively small hydrocarbon reservoirs. The temperature anomalies of the order of 5–7 °C may reflect fluids moving upward along fractures and faults, rather than changes in thermal conductivity resulting from different pore fluids.

Continuous‐temperature depth logs, especially when recorded in boreholes under thermal equilibrium conditions, provide detailed information of the subsurface thermal structure, which is necessary for the determination of reliable heat‐flow and rock thermal properties. In conjunction with independent thermal‐conductivity determinations, thermal logging data also allow the separation of heat conduction effects from thermal convection effects by fluid flow driven by various pressure differences such as pore fluid pressure. The Earth's thermal field is related intimately to geothermal resources and hydrocarbon resources. Therefore, the characterization of temperature in the subsurface and its relationship to lithology is of critical importance.

Different numerical models can be deployed to calculate the matrix thermal conductivity of a rock from the bulk thermal conductivity (BTC), if the effective porosity of the rock is known. Vice versa, using these parameters, the BTC can be determined for saturation fluids of different thermal conductivity (TC). In this paper, the goodness-of-fit between measured and calculated BTC values of sedimentary rocks has been evaluated for two-component (rock matrix and pores) models that are used widely in geothermics: arithmetic mean, geometric mean, harmonic mean, Hashin and Shtrikman mean, and effective-medium theory mean. The examined set of samples consisted of 1147 TC data in the interval 1.0–6.5 W m −1 K −1 . The quality of fit was studied separately for the influence of lithotype (sandstone, mudstone, limestone, dolomite), saturation fluid (water and isooctane), and rock anisotropy (parallel and perpendicular to bedding). From the studied models, the geometric mean displays the best, however not satisfying correspondence between calculated and measured BTC. To improve the fit of all models, respective correction equations are calculated. The “corrected” geometric mean provides the most satisfying results and constitutes a universally applicable model for sedimentary rocks. In addition, the application of the herein presented correction equations allows a significant improvement of the accuracy of existing BTC data calculated on the basis of the other mean models. Finally, lithotype-specific conversion equations are provided permitting a calculation of the water-saturated BTC from data of dry-measured BTC and porosity (e.g., well log derived porosity) with no use of any mixing model. For all studied lithotypes, these correction and conversion equations usually reproduce the BTC with an uncertainty

A holistic understanding of the physicochemical processes induced by CO2 injection and storage in a reservoir is based on a geoscientific characterisation of the overall geological system consisting of reservoir rocks and cap rocks. It requires in a first step a comprehensive baseline characterisation (sedimentological, mineralogical, geochemical, mechanical, etc.) of pertinent parameters and conditions. To properly handle the large amount of different geoscientific information a Data Management System (DMS) was developed, which proved indispensable to conduct such a multi-disciplinary project. The DMS provides a tool for scientific process management, data analysis, integration and visualisation, data transfer and scheduling through specialised database systems and retrieval techniques, storage technology, and efficient data access.

In the framework of the German R&D programme CLEAN (CO2 Large-Scale Enhanced Gas Recovery in the Altmark Natural Gas Field), the geological structure of an area encompassing the Altensalzwedel sub-field and its surrounding was analysed in detail. A 3-D model was developed that contains the major geological formations and their general lithology including the natural gas reservoir (in the Permian Rotliegend), the immediate cap rock (Permian Zechstein) of the reservoir and its overburden. Based on this geological model, a 3-D steady-state thermal model was generated as part of a shared earth model. The parameterisation of the geological model layers with thermal rock properties is based on laboratory and well-log data. The model shows temperature changes in dependence of geological structure and of different rock thermal conductivity. The calculated surface heat flow is high (>80 mW m−2) for most of the area, which is in accordance to measured surface heat flow. Temperature on top of the Rotliegend reservoir is variable ranging from 110 to 150 °C. The quantification of temperature changes versus depth as well as laterally in the reservoir are valuable input data for modelling the dynamic processes of CO2 injection within CLEAN.

The first assessment of temperature conditions in Kansas was made by geothermal gradient computations from temperature measurements in shallow boreholes, and these conditions are related to structural patterns, sedimentary cover and underlying basement properties. The area of south‐central Kansas was selected for detailed study of geothermal character in relation to the geology. The aim was to quantify the relations and to determine the relationship of different variables of the temperature field. Input parameters included geothermal variables of gradient and temperature, and structure and sediment thickness. Two approaches were used: (1) the numerical computation of theoretical temperature‐depth models based on conductive heat transfer, and (2) a map‐comparison technique based on algebraic methods. The temperature field information usable for the map comparison is different in response to different measurements (nonequilibrium BHTs and temperatures from logged measurements in equilibrium). Derived from modelled results (plotted isotherms on cross‐sections), a close relation between gradients and thermal conductivity of the sediments was confirmed. The most noticeable effect on the geothermal field, as noted quantitatively from the map‐comparison study, is the relation of thickness of outcropping Permo‐Pennsylvanian units because of their different thermal conductivity. The eastward increase of mean gradients is inversely related to the total sediment thickness, but this is mostly recognizable using the shallow temperature gradients. This dissimilarity gives additional evidence for a close link between gradients and thermal conductivity of the sediments in which the temperature measurements were made. The effect caused by the structure in deeper (older) units is not important and seems not to be significant, nor is the influence of the basement rock composition as indicated by the temperature modelling.

Quantitative approaches to data analysis in the last decade have become important in basin modeling and mineral-resource estimation. The interrelation of geological, geophysical, geochemical, and geohydrological variables is important in adjusting a model to a real-world situation. Revealing the interdependences of variables can contribute in understanding the processes interacting in sedimentary basins. It is reasonably simple to compare spatial data of the same type but more difficult if different properties are involved. Statistical techniques, such as cluster analysis or principal components analysis, or some algebraic approaches can be used to ascertain the relations of standardized spatial data. In this example, structural configuration on five different stratigraphic horizons, one total sediment thickness map, and four maps of geothermal data were copared. As expected, the structural maps are highly related because all had undergone about the same deformation with differing degrees of intensity. The temperature gradients derived (1) from shallow borehole logging measurements under equilibrium conditions with the surrounding rock, and (2) from non-equilibrium bottom-hole temperatures (BHT) from deeper depths are mainly independent of each other. This was expected and confirmed also for the two temperature maps at 1000 ft which were constructed using both types of gradient values. Thus, it is evident that the use of a 2-point (BHT and surface temperature) straightline calculation of a mean temperature gradient gives different information about the geothermal regime than using gradients from temperatures logged under equilibrium conditions. Nevertheless, it is useful to determine to what a degree the larger dataset of nonequilibrium temperatures could reflect quantitative relationships to geologic conditions. Comparing all maps of geothermal information vs. the structural and the sediment thickness maps, it was determined that all correlations are moderately negative or slightly positive. These results are clearly shown by the cluster analysis and the principal components. Considering a close relationship between temperature and thermal conductivity of the sediments as observed for most of the Midcontinent area and relatively homogeneous heat-flow density conditions for the study area these results support the following assumptions: (1) undifferentiated geothermal gradients, computed from temperatures of different depth intervals and differing sediment properties, cannot contribute to an improved understanding of the temperature structure and its controls within the sedimentary cover, and (2) the quantitative approach of revealing such relations needs refined datasets of temperature information valid for the different depth levels or stratigraphic units.