Salt structures are abundant features in sedimentary basins, locally affecting the
thermal field and therefore may be of special interest for the geothermal exploration
and exploitation. The thermal conductivity of salt is a factor of two or three higher
than that of typical clastic sediments. Thus, heat tends to be focused through a salt
diapir at the expense of heat in the surrounding basal sediments. Consequently,
sediments close to the apex of a diapir are warmer than sediments far from the salt,
while sediments located close beneath the salt and in the rim syncline are cooler. To
quantify these thermal effects for Permian Zechstein salt structures in the Northeast
German Basin (NEGB), 1-D, 2-D, and 3-D thermal modeling was performed. In the NEGB,
the Permian salt was originally deposited with an average thickness of 1000 m.
Whereas the base of the salt bottom is at depth of about 3 – 5 km, the top of the
salt pillows and diapirs sometimes are near the surface. It was observed that
compared to 3-D models, 2D models do overestimate the area of the disturbed
temperature field. The 3-D model of the Gransee salt structures, which consist of
several single salt diapirs as well as combinations of diapir and pillow structures
within an area of 25 x 25 km, changes in heat flow were observed horizontally over a
distance of 5 – 7 km off salt. Within and above the salt, heat flow is increased,
whereby this increase is variable with depth. For example, at the Gransee diapir,
which is 3.5 km thick, 2 – 4 km in diameter, and whose top is at 500 m depth, near
surface heat flow is increased by about 50 mW/m². The greatest increase of
temperature (about 10 – 15 °C) is in a 50 – 100 m-thick interval immediately above
the salt. In the lower part of the salt diapir and its adjacent and underlying
sediments temperatures are reduced by up to 15°C. To perform a proper evaluation of a
specific site and its suitability for geothermal applications, the salt-structure
geometry and the in-situ thermal properties of the salt and of the surrounding rocks
must be known in detail. Different geological settings in terms of salt thickness and
shape and different thermal-conductivity contrasts between salt and surrounding rocks
will provide different results. Thus, the nearly 10-km-thick salt diapirs in the
northern part of the Gulf of Mexico show a stronger increase in temperatures above
the salt (20 – 30 °C in a depth of about 2 km) compared to the conditions in the NEGB.

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