Hydraulic injection tests in the pilot EGS borehole PVGT-LT1 in Litoměřice, Czechia

0576144 - ÚSMH 2024 RIV GB eng J - Journal Article
Fischer, T. - Vlček, Josef - Dědeček, Petr - Řihošek, J. - Zimmermann, G. - Holeček, J. - Mazanec, Martin - Rukavičková, L. - Janků, L. - Káldy, E.
Hydraulic injection tests in the pilot EGS borehole PVGT-LT1 in Litoměřice, Czechia.
Geothermics. Roč. 115, DEC (2023), č. článku 102805. ISSN 0375-6505. E-ISSN 1879-3576
Institutional support: RVO:67985891 ; RVO:67985530
Keywords : Geothermal energy * Hydraulic injection * Seismic monitoring * Stress field
OECD category: Volcanology; Volcanology (GFU-E)
Impact factor: 3.9, year: 2022
Method of publishing: Open access
https://doi.org/10.1016/j.geothermics.2023.102805

Successful utilization of geothermal energy is conditioned by sufficient permeability of the rock formation as a heat exchanger. We present results of hydraulic injection tests carried out in 2020 in the pilot geothermal borehole PVGT-LT1 in Litoměřice, Czech Republic, which samples 800 m of Paleozoic and Mesozoic sediments on the top of a crystalline basement. The low hydraulic conductivity on the order of 10−11 m/s obtained by recovery tests was verified by large-scale injection tests monitored by DTS temperature logging. During the first test, 24 m3 of water were injected and a permeable fracture was created at 880 m depth, breaking through the ignimbrite layer. The opening pressure of 12.55 MPa corresponds to the lower estimate of the minimum stress at this depth. The second injection was performed 7 months later and 202 m3 were injected at flow rates reaching 50 l/min. It showed that the fracture had been preserved since the first injection, which was documented by a non-zero flow rate at the smallest injection pressures and also by a stabilized water level in the borehole, which dropped immediately after the fracture formation. No induced seismicity accompanied the injection, which indicates a possibly low seismogenic potential of this area of the Bohemian Massif. The model of finite conductive fracture fitted to the pressure decay curve during shut-in intervals gives an estimate of a fracture half-length exceeding 100 m.
Permanent Link: https://hdl.handle.net/11104/0345743