Seismic Monitoring During Drilling and Stimulation of Well RN-15/IDDP-2 in Reykjanes, SW-Iceland

Abstract

The Reykjanes geothermal system is located at the southwest tip of the Reykjanes Peninsula in Iceland, precisely where the Mid-Atlantic Ridge comes onshore. It has been utilized for power production by HS Orka since 2006 with a power production of 100 MWe at present. The Horizon 2020 project „Deployment of deep enhanced geothermal systems for sustainable energy business (DEEPEGS)” aims at demonstrating the feasibility of deep enhanced geothermal systems as a competitive energy alternative for commercial use. Within the framework of the DEEPEGS project, the deep geothermal well RN-15/IDDP-2 was drilled at Reykjanes from August 2016 to January 2017, to a total depth of 4659 m, where it reached supercritical conditions. A total loss of circulation was encountered during drilling from 2.5 km depth to the final depth. To monitor the seismic activity during drilling and stimulation of the well, a temporary seismic network was installed in Reykjanes from October 2016 to September 2017, in addition to the permanent seismic network in the area. Interestingly, a zone from roughly 3 to 6 km depth below the producing geothermal field at Reykjanes which was aseismic prior to the deep drilling, became seismically active during drilling and stimulation of the well. Results of the seismic monitoring are presented, giving insight into the geological structures and processes that may be responsible for permeability in the deep reservoir. The seismic catalogue covering the timespan from the start of drilling to the end of the main stimulation phase contains over 2300 earthquakes, which have been manually picked. Fault plane solutions are computed to help characterize the local stress field, and the spatial and temporal development of the seismicity is used to investigate fractures created and/or re-activated during the drilling and stimulation. Hence, we aim at gaining knowledge and understanding of the architecture of the deep part of the reservoir at Reykjanes.