| Abstract |
The Rittershoffen deep geothermal plant, which is located 6 km east of Soultz-sous-Forêts (France), is operated since mid-2016 by the ECOGI joint venture. It is the youngest deep geothermal site exploited in the Upper Rhine Graben, several are currently under development in this area. The reservoir produces hot water at 170°C and delivers 24 MWth to a bio-refinery located 15 km away. This field was developed from 2012 to 2016. The first well of the doublet (GRT-1) was completed end of 2012 and reaches the crystalline fractured basement which constitutes the reservoir formation together with the overlaying Buntsandstein sandstones. A reservoir development strategy was defined, and first consisted in enhancing the connections between GRT-1 and the fractured reservoir. These operations were applied in two sequences, respectively in April 2013, with a “thermal†stimulation and in June 2013, with a “hydraulic†stimulation. Both sequences generated seismicity that was not felt by the local population, the maximum magnitude reached 1.6 Mlv. The stimulations were successful, providing the expected enhancement of the hydraulic properties of the well. The drilling of the second well, GRT-2, which ended in July 2014, was followed by a production test highlighting good well productivity and no stimulation was carried out. We present here the seismicity which was detected and located at Rittershoffen until the end of the GRT-2 well drilling. This seismicity was acquired by a permanent seismic network and several additional temporary stations implemented over the period. Event detection was carried out by the SeisComp3 software adapted for local seismicity processing and tuned, a posteriori, to the seismicity recorded at Rittershoffen. Following the automatic detection, manual review and picking was carried out and location was performed in a 3D velocity model derived from active seismic and well logs. More than 1300 events constitute the so-called reference database. We present the time, space and magnitude characteristics of the induced seismicity and discuss them in parallel with the operational parameters in order to better understand the reservoir behavior and the well doublet system at depth. |