Abstract
We present a new method to incorporate paleo-surface temperature effects in steady state 3D conductive temperature models. The workflow approximates the transient effects and incorporates these into steady state models, using appropriate source and sink terms for radiogenic heat production. This allows for rapid models, which can be easily used in ensemble approaches for data assimilation of high-resolution temperature models for geothermal resource assessment. The workflow is demonstrated for the Netherlands which is a sedimentary basin with a wealth of deep (temperature) data from groundwater and oil and gas wells and past studies on the 3D temperature distribution. 3D subsurface temperature models of the Netherlands ranging up to 5 km depth systematically overpredict temperatures at shallow (<1500 m) depth. Analysis of both shallow (<600 m, >200,000 measurements) and deep temperature measurements (1–6 km, >1500 measurements), clearly demonstrates a shallow thermal gradient in over 200 locations of ~20 °C km −1 for the top 400 m underlain with a deep geothermal gradient of ~31 °C km −1 for the 2–4 km interval. Improvements in 3D subsurface modelling regarding the shallow part are accomplished by adding a paleo-surface temperature correction related to glaciation effects of the Weichselian glacial period. This paleo-surface temperature correction proved to be the missing link between two distinctive geothermal gradients observed and is consistent with earlier findings for limited datasets. The consistent overprediction of modelled temperatures in 74% of locations for the top 2 km which are regularly distributed over the Netherlands demonstrates that the influence of paleo-surface temperatures is rather uniform over large areas and not significantly overprinted by other effects such as groundwater flow. The updated model, marked by up to 10 degrees cooling compared to models ignoring the paleo-surface temperature effects, has major implications for assessing geothermal resource potential up to 2 km depth. • Novel approach for modelling paleo surface temperature effects in thermal models for sedimentary basins. • High resolution integrated deep and shallow database for validation of thermal effects of paleo surface temperatures. • Improved thermal model shows excellent fit with observations.
Highlights
Geothermal energy is a renewable energy source that is sustainable for future generations and available autonomous of seasonal fluctua tions or changing climate conditions
On continental scale -outside magmatic areas marked by strong transient effects- mostly 1D thermal conductive models have been used for resource assessment (e.g. Limberger et al, 2014; Limberger et al, 2018), whereas on more regional scale, in various countries high resolution 3D thermal models have been constructed constrained by temperature data from deep boreholes (e.g. Bonte et al, 2012; Gola et al, 2017; Bekesi et al, 2020). 3D steady state conductive models are very effective in terms of computational performance for high resolution models (e.g. Bekesi et al, 2020)
The model is marked by a steady state geotherm for the top 10 km, with radiogenic heat production of A = 3.6 μW m− 3, thermal conductivity of k = 2 W m− 2 K− 1
Summary
Geothermal energy is a renewable energy source that is sustainable for future generations and available autonomous of seasonal fluctua tions or changing climate conditions. On continental scale -outside magmatic areas marked by strong transient effects- mostly 1D thermal conductive models have been used for resource assessment In regions marked by relatively rapid sediment and erosion and active tectonism, temperature distributions can be strongly affected Hydrothermal fluid flow and associated heat advection-mostly observed more locally- can give rise to strong alteration of the steady state predictions, even at a few km depth Paleo-surface temperature changes, in particular the effects of past glaciations can strongly affect the observed surface heat flow values and temperature gradient in the top few km of the earth and give rise to relative low geothermal gradient in the top 1–2 km of the crust and sediments relative to the deeper part, which is well recorded in bore holes Paleo-surface temperature changes, in particular the effects of past glaciations can strongly affect the observed surface heat flow values and temperature gradient in the top few km of the earth and give rise to relative low geothermal gradient in the top 1–2 km of the crust and sediments relative to the deeper part, which is well recorded in bore holes (e.g. Ter Voorde et al, 2014)
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