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Abstract

Focus on the utilization of geothermal energy as a sustainable energy source has resulted in extensive geothermal exploration activities with a demand for procedures for obtaining reliable information on subsurface temperatures and thermal resources. Subsurface thermal information is basically obtained from two different sources: direct observations by measurements in boreholes and indirectly by numerical modelling. We present a methodology which ensures consistency between model temperature predictions and measured temperatures and which provides easily updated models. Structural and lithological information, data on rock thermal properties and current information on borehole temperatures and heat flow are integrated into a parameterised 3D subsurface model, for which the heat equation is solved by applying combined numerical forward modelling and inverse optimisation methodology. A priori values of model thermal parameters, such as thermal conductivity and heat production, as well as background heat flow may be adjusted, within uncertainty limits, to ensure model agreement between observed borehole temperatures and resulting model estimates. Inverse parameter calibration is carried out by minimising an objective function comprised of a weighted sum of the squared differences between modelled and measured temperatures. This methodology is applied to Danish and North German sedimentary basins. The resulting thermal models include temperature predictions in a densely spaced 3D grid of subsurface points. Temperature information may be extracted in terms of local temperature-depth profiles, temperature maps for specified geological horizons, such as potential geothermal reservoirs or for selected constant depth. Such models improve our understanding of the subsurface thermal field, including sources of temperature variations and anomalies, and facilitate risk reduction by integration into regional as well as local geothermal exploration.