TY  - JOUR
A1  - Hofmann, Hannes
A1  - Zimmermann, Günter
A1  - Farkas, Márton Pál
A1  - Huenges, Ernst
A1  - Zang, Arno
A1  - Leonhardt, Maria
A1  - Kwiatek, Grzegorz
A1  - Martinez-Garzon, Patricia
A1  - Bohnhoff, Marco
A1  - Min, Ki-Bok
A1  - Fokker, Peter
A1  - Westaway, Rob
A1  - Bethmann, Falko
A1  - Meier, Peter
A1  - Yoon, Kern Shin
A1  - Choi, JaiWon
A1  - Lee, Tae Jong
A1  - Kim, Kwang Yeom
T1  - First field application of cyclic soft stimulation at the Pohang Enhanced Geothermal System site in Korea
JF  - Geophysical journal international
N2  - Large-magnitude fluid-injection induced seismic events are a potential risk for geothermal energy developments worldwide. One potential risk mitigation measure is the application of cyclic injection schemes. After validation at small (laboratory) and meso (mine) scale, the concept has now been applied for the first time at field scale at the Pohang Enhanced Geothermal System (EGS) site in Korea. From 7 August until 14 August 2017 a total of 1756 m(3) of surface water was injected into Pohang well PX-1 at flow rates between 1 and 10 l s(-1), with a maximum wellhead pressure (WHP) of 22.8 MPa, according to a site-specific cyclic soft stimulation schedule and traffic light system. A total of 52 induced microearthquakes were detected in real-time during and shortly after the injection, the largest of M-w 1.9. After that event a total of 1771 m(3) of water was produced back from the well over roughly 1 month, during which time no larger-magnitude seismic event was observed. The hydraulic data set exhibits pressure-dependent injectivity increase with fracture opening between 15 and 17 MPa WHP, but no significant permanent transmissivity increase was observed. The maximum magnitude of the induced seismicity during the stimulation period was below the target threshold of M-w 2.0 and additional knowledge about the stimulated reservoir was gained. Additionally, the technical feasibility of cyclic injection at field scale was evaluated. The major factors that limited the maximum earthquake magnitude are believed to be: limiting the injected net fluid volume, flowback after the occurrence of the largest induced seismic event, using a cyclic injection scheme, the application of a traffic light system, and including a priori information from previous investigations and operations in the treatment design.
KW  - Cyclic soft stimulation (CSS)
KW  - induced seismicity
KW  - risk mitigation
KW  - enhanced geothermal systems (EGS)
KW  - granite
KW  - Pohang (Korea)
Y1  - 2019
U6  - https://doi.org/10.1093/gji/ggz058
SN  - 0956-540X
SN  - 1365-246X
VL  - 217
IS  - 2
SP  - 926
EP  - 949
PB  - Oxford Univ. Press
CY  - Oxford
ER  -