Update Heat Flow Density Map for Portugal

New thermal conductivity, heat production and temperature data obtained in Portugal were used to produce a new heat flow density map. Heat flow density values in Portugal vary between 42 and 115 mW/m2 and allow the extrapolation of temperatures to depths not yet reached by existing boreholes. Additionally, temperature maps at 500 and 1000 m depths and a two-dimensional model constructed along a north-south profile in the area where there is more geothermal information are given

Reconstruction of the Past Climate in Southern Portugal from Geothermal Data

The study of the past climate in the territory of mainland Portugal using geothermal data started in 1996. From an initial set of about 90 temperature logs obtained Portugal, eight were chosen as good for estimating ground surface temperature (GST) in the past. The main results from the analysis of the collected geothermal data show, on average, that there has been an increase of the atmosphere mean surface temperature of about 1 K since the middle of the nineteenth century. This conclusion agrees with the results obtained from the analysis of air temperature records that were obtained in the Lisbon weather station since 1856. With the objective of improving the reconstruction of GST history in Portugal one of the eight wells (the TGQC-1 well) was cased and is being used for repeated temperature logging since 1997. The results of the temperature measurements repetition indicate that the warming trend continues to the present day, accelerating in the last 10 to 15 years. Since 2005 a geothermal climate change observatory was installed in the TGQC-1 well to study the air-ground coupling

A coupled geothermal model of the Alpokalja area, Hungary—Austria

A coupled groundwater flow and heat transport model was developed for a trans-boundary geothermal reservoir located in the Alpokalja area. The study area lies in the western part of the Pannonian Basin, at the border between Hungary and Austria. The study area contains several famous geothermal water utilizations on both sides of the border, which has an impact on natural groundwater conditions. The aim of the modeling study was to evaluate the natural-state and production-state groundwater conditions, and to make predictions on cross-boundary interferences. A three-dimensional finite element-type coupled geothermal model was constructed to provide a coherent quantitative representation of geothermal flow systems. The model described the hydraulic behavior of the flow system, the interaction between different reservoirs, and geothermal conditions

On the possibility of using geothermal data for paleoclimate studies in Antarctica: the experience from Portugal

The study of the climate in the past and the climate change in mainland Portugal using geothermal data has started in 1996. Reconstruction of ground surface temperature (GST) history from temperature logs measured in a 200 m deep borehole located 5 km away from the town of Évora in Portugal, indicates a warming of 1K since the second half of the nineteenth century to the middle of the 90s of the twentieth century, increasing considerably in the last 10 years. Results of the reconstruction (based on a functional space inversion – FSI – method) are compared with air temperatures recorded at the Lisbon meteorological station since 1856. The air temperature time series display a warming trend with the amplitude about 1K for the same period. The coupling of the air and ground temperature changes and their downward propagation by heat conduction was confirmed by repeated logging in November 2003, 6.7 years after obtaining the first temperature log. The method can be used in paleoclimatic studies in Antarctica as well as in areas with permafrost

Thermal contraints on high-pressure granulite metamorphism of supracrustal rocks

The circumstances leading to the formation and exposure at the Earth's surface of supracrustal granulites are examined. These are defined as sediments, volcanics, and other rock units which originally formed at the surface of the Earth, were metamorphosed to high-pressure granulite facies (T = 700-900 C, P = 5-10 kbar), and reexposed at the Earth's surface, in many cases underlain by normal thicknesses of continental crust (30-40 km). Five possible heating mechanisms to account for granulite metamorphism of supracrustal rocks are discussed: magnetic heating, thermal relaxation of perturbed temperature profiles following underthrusting of the continental crust, thermal relaxation after underthrusting of thin slivers of supracrustal rocks below continental crust of normal thickness, major preheating of the upper plate, and shear heating caused by frictional stress along the thrust plane

GEOTHERMIC STATUS OF THERMOPYLAE - ANTHILI AREA IN FTHIOTIDA PREFECTURE

The purpose of this study was the discovery, identification and evaluation of directly exploitable geothermal fields, in the Thermopylae - Anthili area (100km2 ). After the evaluation and the processing of any preexisting data, followed the surface works, such as further geological mapping, tectonic and stratigraphic correlations and analyses, geothermal impressions, observations at 30 recorded points (springs, drillings, wells) regarding water sampling, chemical analyses, temperature, pH and conductivity measurements, special sampling for Br and isotopes analyses. The in depth works that took place concern geophysical prospecting, loggings, small and large diameter drillings. All the data were digitized and processed in a GIS environment. After correlating all the data collected for the region, a geological - geothermal model was constructed. According to this model, water percolates through permeable formations, joints and faults, gets mixed with the existing salt water, warms up and then ascends to the surface through faults and concentrates on proper reservoirs. Specifically, the region of Damasta where two areas of hot water reservoirs have been identified is of particular geothermal interest. The first, located in Triassic– Jurassic limestones (more than 600m deep), presents the greatest interest in terms of temperature and capacity, while the second (found on the surface and up to 350m deep) is located in Quaternary sediments and the upper formations of the underlying Late Cretaceous limestone

Monitoring a shallow geothermal experiment in a sandy aquifer using electrical resistivity tomography: a feasibility study

Geothermal resources, especially groundwater resources, are increasingly used around the world. It is therefore necessary to improve the characterisation of thermal parameters of the aquifers. This is done mostly with thermal response tests. In this work, we monitored with electrical resistivity tomography a geothermal test on the campus of Ghent University (Belgium). We injected warm water (45°C) into a sandy aquifer where the groundwater has a temperature of 10°C at a rate of 100 liter/hour during three days. Laboratory measurements indicated that we could expect at most a change of 2%/°C of the water electrical conductivity. The time-lapse series of electrical images show clearly the thermal plume corresponding to the injected water with a maximum change of minus 20% after 72 hours of injection. A comparison with a geothermal model shows that the anomaly is well detected but also distorded due to the inversion regularization (smoothness constraint). ERT enabled to follow the evolution of the injected heated water with more spatial coverage that traditionnal techniques. ERT is thus an interesting tool to monitor the exploitation of geothermal resources. In the future, it will be necessary to improve the inversion process to use quantitavely such results in a calibration process