New stratigraphic interpretation of the Soultz-sous-Forêts geothermal wells based on Rittershoffen (Upper Rhine Graben, France)

Abstract

In Northern Alsace, the Soultz-sous-Forêts pilot project for power production is the first on-going geothermal site. In this geothermal project, most attention was focused on the basement and the sedimentary cover/basement interface. It follows that the sedimentary part from the drilling (around 1.4 km thick) was never really investigated. The main challenge of this work is therefore to re-interpret the old wells’ data in order to give a precise and detailed chrono-lithostratigraphic log for GPK-1 and GPK-2 especially in their sedimentary part. These new investigations of the GPK’s wells have been possible thanks to the new data collected in the recent geothermal wells at Rittershoffen (GRT-1 and GRT-2, spaced of 6.5 km from Soultz-sous-Forêts) characterized by a quiet complete stratigraphic succession. Both sites have been explored by deep drilling operations aiming to exploit the heat extracted from a deep granitic basement (Paleozoic) covered by a stack of 2.2 km thick sedimentary rocks (Mesozoic to Cenozoic). Thus, the Rittershoffen’s chrono-lithostratigraphic logs have been used as a baseline in order to interpret the sedimentary succession from GPK-1 and GPK-2. As a conclusion, the GPK-1 and GPK-2 well logs will be paralleled for stratigraphic comparisons. Four major faults were highlighted. This extended abstract summaries the research reported in Aichholzer et al. (2016).