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Abstract

Information of subsurface temperature distribution in the Danish area originates from direct measurements in boreholes and from indirect theoretical modelling. “Point observations” of varying quality are available as industrially measured “Bottom Hole Temperatures” from deep exploration boreholes, and accurate continuous equilibrium temperature logging has been carried out in a number of accessible deep boreholes. A regional distribution of subsurface temperatures is obtained by combining measurements and 3D numerical modelling in which the heat equation is solved. Modelling results are constrained by observations in terms of available measured temperatures and observed surface heat flow. Information on subsurface thermal conductivity, which is a critical parameter, is obtained from core measurements and well-log analyses. Interval temperature gradients are found to vary by a factor of three to four across lithologies of different conductivity. Mean geothermal gradients from surface to depths of 1000 to 3000 m are generally between 20 and 30 °C/km. As an example, modelled temperatures for the Gassum geothermal reservoir are shown with temperatures largely between 35 and 90 °C for depths of interest.