Temperature and hydraulic properties of the Rittershoffen EGS reservoir, France

Abstract

The ECOGI geothermal doublet, located in Northern Alsace (France) is designed to deliver a power of 24 MWth to the “Roquette Frères” bio-refinery. Two deep wells have been drilled in 2012 (GRT-1) and 2014 (GRT-2). Both wells target the same faulted zone in the crystalline basement.
Numerous temperature logs have been realised in both wells, suggesting a diffusive temperature regime above the Muschelkalk limestone and an advection-dominated temperature regime below the top of this formation, that means mainly in the Buntsandstein sandstone and the granite. Moreover, main flow zones are clearly correlated with temperature anomalies, suggesting important natural flows in the targeted fault zone. Due to a low initial productivity index, an extended well development sequence has been realised in well GRT-1, including low-rate cold fluid injections, localized chemical injections and hydraulic stimulations, and leading to a great improvement of the hydraulic well properties. Thanks to its high initial productivity index, well development was not necessary in GRT-2. Then, numerous pumping tests were carried out in GRT-2 as well as an interference and tracer tests has been done between wells GRT-1 and GRT-2.
Thus, we propose an integrated interpretation of data gathered during these experiments in order to characterize at best the hydrothermal properties of the Rittershoffen EGS reservoir.