WG 3: Potential methods

This group surveys the evolution of the subsurface during geothermal exploitation (specifically at the Soultz-sous-Forêts and Rittershoffen geothermal sites) and explores for deep resources using gravimetric and magnetotelluric (MT) methods.

It uses the tecniques such as electromagnetism and hybrid micro-gravity monitoring (combination of these different types of gravimeters) and demonstrate how they contributes to the sustainable management of renewable energy. For instance, the gravity method highlights the mass redistribution and, consequently, helps to quantify the mass transfer (recharge/discharge) within the geothermal reservoir.

The group has applied the hybrid gravity technique to the Theistareykir geothermal field in North Iceland that produces 90 Mwe since 2018. On one hand, it uses a relative micro-gravity network of 27 stations measured from 2017 to 2022 i.e. before and after the beginning of the geothermal production, with a Scintrex CG5 relative gravimeter (RG). On the other hand, in the frame of a cooperation with GFZ Potsdam, it also benefits from the continuous gravity changes recorded at 3 permanent stations with iGrav superconducting gravimeters (SG). These meters are calibrated with a FG5 ballistic absolute gravimeter (AG) belonging to EOST and the yearly AG campaigns allow us to remove the (small) instrumental drift of the iGravs.

The hybrid micro-gravity method (RG, SG and AG) is used to investigate the gravity changes in relation to geothermal activity parameters like injection and extraction rates. The comparison of the gravity changes due to mass redistribution to what is expected from the injection/extraction rates allows us to speculate on the sustainability of the Theistareykir power plant since the start of exploitation in terms of discharge/recharge of the geothermal reservoir.

Every year (2020, 2022, 2023 and 2024) multiple measurements are carried out one absolute measurement (with Micro-g Solutions FG5 absolute gravimeter) at reference stations in Krafla, and micro-gravity through a network of 20 stations in Theistareykir. A mass budget estimate was recently attempted on the period 2019-2022 and one important result is that a partial recharge of the geothermal reservoir must occur in order to explain our observed surface gravity variations with respect to the known exploitation parameters (injection and production rates).

• Members (EOST/ITES): Jacques Hinderer, Guy Marquis, Clara Jodry

With the other ITI GeoT WGs:

WG4: Rocks physics

With other academic partners:

University of Iceland (F. Sigmundsson, C. Lanzi)

Università ‘‘Federico II’’ di Napoli, Naples, Italy (U. Riccardi)

GFZ Potsdam, Germany (P. Jousset,  B. Giuliante)

With socio-economic partners:

Landsvirkjun, Iceland (A. Mortensen)

Icelandic Meteorological Office (V. Drouin)

ONERA, France (N. Portier)

Hybrid microgravity monitoring of the Theistareykir geothermal reservoir (North Iceland). Portier, N., Forster, F., Hinderer, J., Erbas, K., Jousset, P., Drouin, V., Li S., Sigmundsson, F., Magnússon, I., Hersir, G., Ágústsson, K., Guðmundsson, A., Júlíusson, E., Hjartasson, H.,  & Bernard, J.-D.,  (2022). Pure Appl. Geophys., 179, 1935–1964. https://doi.org/10.1007/s00024-022-03018-8

Intercomparing Superconducting Gravimeter Records in a Dense Meter-Scale Network at the J9 Gravimetric Observatory of Strasbourg, France. Hinderer, J., Warburton, R.J., Rosat, S., Riccardi, U., Boy, J., Forster, F., Jousset, P., Güntner, A., Erbas, K., Littel, F., & Bernard, J.D. (2022). PAGEOPH, 179, 1701 - 1727. https://doi.org/10.1007/s00024-022-03000-4

Environmental and anthropogenic gravity contributions at the Þeistareykir geothermal field, North Iceland. Forster, F., Güntner, A., Jousset, P., Reich, M., Männel, B., Hinderer, J., & Erbas, K., (2021). Geotherm Energy 9, 26. https://doi.org/10.1186/s40517-021-00208-w

Performance of three iGrav superconducting gravity meters before and after transport to remote monitoring sites. Schäfer, F., Jousset, P., Güntner, A., Erbas, K., Hinderer, J., Rosat, S., Voigt, C., Schöne, T., & Warburton, R. (2020). Geophys. J. Int.,  223, Issue 2, , 959–972. https://doi.org/10.1093/gji/ggaa359