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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.

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

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.

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.

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.

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.

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.

Since April 2004, preparatory work prior to CO2 injection has been conducted in the CO2SINK Project, the European Union's first research and development activity on the in-situ testing of geological storage of CO2 near the town of Ketzin, Germany. Carbon dioxide will be injected into a saline aquifer of the Triassic Stuttgart Formation in an anticlinal structure of the northeast German Basin. The drilling of one injection and two observation wells will commence at the end of 2006. The predrilling phase focuses on the baseline geological parameters of the anticline. The Stuttgart Formation is lithologically heterogeneous; it consists of sandy channel-(string)-facies rocks, with good reservoir properties alternating with muddy flood-plain-facies rocks of poor reservoir quality. Playa-type rocks form the immediate cap rock above the CO2SINK reservoir. A geostatistical approach has been applied to describe the reservoir architecture between and beyond well control. This model forms the basis for the generation of reservoir-dynamic models of CO2 injection that assist in the planning of injection operations and in the understanding of CO2 plume evolution. A verification of the geometry of the reservoir and the structural situation of its overburden is expected from a three-dimensional baseline seismic survey that was conducted in the autumn of 2005. Laboratory experiments under simulated in-situ conditions were performed to evaluate the geophysical signature of rocks saturated with CO2. The chemical composition of the groundwater and the CO2 flux in the soil were analyzed across the Ketzin anticline, providing the baseline for a monitoring program during and after injection of CO2, targeted at the detection of potential CO2 leakage from the storage reservoir.

The AIG10 borehole provided direct access to hydraulic conditions. The first results of two open-hole pumping tests and one artesian production test are presented. From the first pumping test in the conglomerates, a hydraulic conductivity of 10−5– 10 −4 m s −1 was derived and it was suggested that there is a closed hydraulic system bounded by the Aigion Fault zone and other faults farther north. A second pumping test, in the Olonos–Pindos limestones, showed artesian flow (water pressure of 0.5 MPa and flow of 1.9×10 −4 m 3 s −1 ). The transmissivity is about 4×10 −6 m 2 s −1 . Below the fault zone, pressure and flux increased, suggesting karstic water-flow conditions. Water-pressure difference of more than 0.5 MPa between the hangingwall and the footwall provides evidence that the Aigion Fault zone acts as an impervious zone. An artesian production test for the interval 708–1001 m showed a fluid pressure of >1 MPa and natural flow of 1.5×10 −2 m 3 s −1 . A transmissivity of 2– 3 ×10 −4 m 2 s −1 was determined. A preliminary conceptual hydrogeological model, containing flow parameters and flow paths, is developed, based on data from AIG10 and other wells and springs. To cite this article: V. Giurgea et al., C. R. Geoscience 336 (2004).

Aquifer properties can be evaluated by monitoring artificially stimulated fluid movements between wells, if the fluid is heated. Changes in the temperature profile recorded in observation wells indicate the flow path of the heated fluid, which in effect acts as a tracer. A fluid-flow experiment in the Cretaceous Dakota Formation at the Hodgeman County site, west-central Kansas, demonstrated the advantage of using the distributed optical-fiber temperature sensing method for monitoring transient temperature conditions in this hydrological application. The fluid flow in the aquifer was increased by producing water from a pumping well and injecting heated water in an injection well 13 m (43 ft) distant from the pumping well. The time-temperature series data obtained and compared with results from previous pumping tests point to interwell heterogeneity of the aquifer and to a zone in the sandstone aquifer of high hydraulic conductivity. However, the experiment would have allowed further clarification of aquifer heterogeneity and thermal properties if at least one observation well had been present between the injection and production wells.