Abstract
Samples of flowback water from a 4.3 km deep geothermal borehole in granite (Pohang, South Korea) were collected following a period of hydraulic stimulation by injection of surface water. Electrical conductivity, temperature and water chemistry of the flowback water were measured. To a first approximation, the data conform closely to a simple ‘mixing tank’ model, with an exponential trend between two end members: an initial injected surface water to a more brackish ‘resident groundwater’ composition. Significant deviation from the ‘mixing tank’ trend would be an indication of significant recent water-rock interaction or other anomalous factors. Such a deviation can tentatively be seen in Na+/Cl- data, especially between 88 and 200 m3 flowback (2.8 to 8.8 hr).
Highlights
Samples of flowback water from a 4.3 km deep geothermal borehole in granite (Pohang, South Korea) were collected following a period of hydraulic stimulation by injection of surface water
Significant deviation from the ‘mixing tank’ trend would be an indication of significant recent water-rock interaction or other anomalous factors
The site was originally intended as an Enhanced Geothermal System (EGS) installation, where hydraulic stimulation has attempted to create a fracture connection in the granite between the two boreholes, forming a heat exchange surface [3]
Summary
Samples of flowback water from a 4.3 km deep geothermal borehole in granite (Pohang, South Korea) were collected following a period of hydraulic stimulation by injection of surface water. Significant deviation from the ‘mixing tank’ trend would be an indication of significant recent water-rock interaction or other anomalous factors. Such a deviation can tentatively be seen in Na+/Cl- data, especially between 88 and 200 m3 flowback (2.8 to 8.8 hr). The site was originally intended as an Enhanced Geothermal System (EGS) installation, where hydraulic stimulation has attempted to create a fracture connection in the granite between the two boreholes, forming a heat exchange surface [3]. A subsequent magnitude (MW) 5.5 earthquake in November 2017 [4], with hypocentre no more than hundreds of metres from the injection points, has halted further operations, while possible causes are
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
