Data assimilation for the investigation for temperature variations in the Paris Basin and the Netherlands

Abstract

Deep geothermal energy systems, intended mostly for the direct use of heat, have been attracting increasing levels of interest in the past 10 years in Western Europe. Both in the Netherlands, where the sector took off with the first system in 2005, and in France, where there has been a resurgence in interest after a 20-year gap, geothermal energy is seen as a key player for a sustainable future. To support the development of deep geothermal energy systems, the scientific community has been working on tools that could be used to highlight areas of potential interest for geothermal exploration. In the Netherlands, ThermoGIS is one such tool that has been developed to inform the general public, policy makers, and developers in the energy sector of the possibility of geothermal energy development. One major component incorporated in this tool is the temperature model.
For both the Netherlands and the Paris Basin (the northern basin in France, which has proved to be of particular interest for the development of geothermal energy), we created thermal models at the lithospheric scale that focus on the first few kilometres of the subsurface for deep geothermal exploration. This regional thermal modelling concentrates on the variations of geological thermal conductivity and heat production both in the sediments and in the crust. In addition, we carried out special modelling in order specifically to understand convectivity in the basin. This modelling focuses on variations at a regional scale. At this scale, the aim of this work is to build on these models and, using data assimilation, to discriminate in the actual causes of the observed anomalies.
The temperature results obtained for the Netherlands show some thermal patterns that relate to the variation of the thermal conductivity and the geometry of the sediments. There is also strong evidence to indicate that deep convective flows are responsible for thermal anomalies. In the Paris Basin, the thermal conductivity has a distinctive impact on the thermicity but the deeper anomalies are impacted by the variations in thermal conductivity and radiogenic heat production in the pre-Mesozoic.