Since the 1980s, much effort has been devoted to the investigation of the thermal
field in Europe culminating in regional mapping projects, such as the ‘Geothermal
Atlas of Europe’ published in 1992 and the ‘Atlas of Geothermal Resources in Europe’
released in 2002. These maps form a broad base to assess Europe’s thermal field on a
global scale. They are based on information from a huge amount of boreholes, whereby
a great portion of these data stems from the exploration for hydrocarbons. Using
these data, stored in national databases and updated whenever new data are available,
assessments of the thermal potential have been made at regional and even at local
scale to develop geothermal prospects.
Simultaneously, a wealth of new data has become available over the past two decades
on the thermal signature of the deeper crust and lithosphere. The signature is
largely derived from tomography data, closely linked to deep seismic reflection, and
earthquake data. The interpretation of deep crustal and lithospheric temperatures
from these data requires careful tectonic interpretation and integrated lithospheric
process models. The interpreted deep lithosphere and crustal temperatures reveal at
some points a strong relation with the measured surface heat-flow pattern. This is
best reflected in areas of great lithosphere thickness (e.g. the Precambrian and
Caledonian terranes), which show lower heat flow and temperature at drillable depth
than areas with lithosphere thinning. Active tectonic settings can result in strong
dynamic effects of crustal and lithospeheric heat flow, which can help predicting and
understanding regional patterns in heat flow, constraining exploration assumptions. 
However, of less global significance, but usually of great importance to the
temperatures in a particular area, are relative shallow (< 10 km) static and dynamic
phenomena such as (1) magma intrusions into high crustal levels (e.g. the Larderello
field); (2) thermal conductivity variations, both vertical and horizontal as they
occur in sedimentary basins; (3) large- and small-scale fluid flow (e.g. the Rhine
Valley); and (4) radiogenic sources in the upper crust (e.g. areas of
high-heat-production granites). The scale of control on temperatures by these global-
and regional-scale processes is variable and many examples now are available to
quantify these effects.
In the exploration of EGS, geothermists are in the comfortable situation to profit
from efforts made in the last several decades by heat-flow researchers in the
assessment of the quality of thermal data used for heat-flow calculation. Thus, there
are excellent examples in the literature showing the advantages of temperature logs
to single temperature data (BHTs, DSTs) to explore the thermal state and the thermal
signatures of an area. In a heat conduction geological environment, the most basic
parameter affecting subsurface temperature is the thermal conductivity of rocks.
Assessments were made on the different quality of thermal conductivity measured in
the laboratory either from core or sample cuttings. Although it is common knowledge
that information on thermal conductivity changes in an exploration setting is
important, data on these changes are difficult to obtain. The measurement of thermal
conductivity has been labour-intensive and thus usually not part of conventional
laboratory programs. However, the optical-scanning technology currently is readily
available to measure efficiently and at low cost the thermal conductivity of many
rock samples in the laboratory. The second obstacle in getting an appreciation of
thermal conductivity is the lack of rock samples in industrial exploration. In
addition, laboratory measurements in some situations are unreliable, especially for
shales, one of the most abundant lithologies in sedimentary basins. For this reason,
a general methodology to obtain thermal conductivity from a set of well-log
parameters is sought and convincing approaches already have been obtained. With good
control of thermal conductivity versus depth, the variation of heat flow versus depth
can be delineated in interpreted in terms of heat-transfer processes, which again is
essential for the assessment of an EGS. 
In summary, temperature/heat-flow techniques, bridging several disciplines in earth
sciences, need to form an integral part in the exploration for geothermal resources,
and for the EGS in particular. Although the general picture of Europe’s heat
anomalies is known, much work needed to decipher the local situation and for
particular prospects, the boundary conditions for the development of an EGS. Measures
to be taken need to involve a critical screening of thermal data, developing baseline
temperature models, and investigating the modification through the time of reservoir
exploitation, providing the essential thermal rock properties, and combining the
temperature field properties with reservoir properties. Examples are needed on how
predictions of the temperature at depth may fail by improper use of subsurface data
or by insufficient exploration.

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