Long-term Continuous Magnetotelluric Monitoring of the IDDP-2/RN-15 Well (Reykjanes Peninsular, Iceland)
Nadine HAAF, Eva SCHILL
[Karlsruhe Institute of Technology, Germany]
The Horizon 2020 project Deployment of deep enhanced geothermal systems for sustainable energy business (DEEPEGS) aims at demonstrating advanced engineering technologies in geothermal reservoirs. During the deepening of the former 2,500 m deep RN-15/IDDP-2 well on the Reykjanes peninsular in the framework of the Icelandic Deep Drilling Program to 4,659 m depth (RN-15/IDDP-2 well) between August 2016 and January 2017 partly total fluid loss and induced seismicity occurred along the drilling path (Friðleifsson et al. 2017). With the aim to prove the suitability of electromagnetic methods for monitoring processes occurring during reservoir engineering such pressure changes or induced seismicity, continuous magnetotelluric (MT) monitoring was carried out between December 2016 and July 2017 with a sampling frequency of 512 Hz at the GUN station, which is located about 1 km to the SE of the RN-15/IDDP-2. The station was equipped with two electric dipoles in N-S and E-W direction, as well as three magnetic sensors oriented in N, E and vertical direction. Single site processing using the birrp code (Chave and Thomson 2004), was applied in order to avoid eliminating sought-for high frequency signals induced during reservoir engineering. However, decimation to lower frequencies and appropriate notch filters were applied to increase the signal-to-noise ratio (Haaf et al. 2019). First results from the drilling period show significant decrease in electric resistivity at frequencies of 0.25 – 5 Hz occurring about 24-48 hours prior to "major" seismic events (ML more than 1.0 or frequencies more than 10/d). Furthermore, decrease in electric resistivity in the frequency range of about 0.2 - 0.125 Hz correlates with time periods of large losses of circulation fluids. These insights are compared to the results from the long-term stimulation of the well between end of January to June 2017, when the well was stimulated under different low and high flow-rate condition. References Chave, Alan D.; Thomson, David J. (2004): Bounded influence magnetotelluric response function estimation. In Geophysical Journal International 157 (3), pp. 988–1006. DOI: 10.1111/j.1365-246X.2004.02203.x. Friðleifsson, Guðmundur Ómar; Elders, Wilfred A.; Zierenberg, Robert; Weisenberger, Tobias B.; Harðarson, Björn S.; Stefánsson, Ari et al. (2017): IDDP-2-Completion-websites-IDDP-DEEPEGS-5: Scientific Drilling, (23, 1-12.). Haaf, N.; Schill, E.;(2019): Processing of magnetotelluric data for monitoring changes during drilling operation. PROCEEDINGS, 44th Workshop on Geothermal Reservoir Engineering (February 11-13).
|        Topic: Geophysics||Paper Number: 13064|