Cyclic Hydraulic Stimulation Design to Develop Enhanced Geothermal Systems (EGS)

Abstract

Enhanced Geothermal Systems (EGS) are required to extract economic amounts of heat from low permeable geothermal reservoirs. We present hydraulic stimulation scenarios applying various cyclic water injection design. The general aim is to reduce the risks of unwanted seismic events beyond a certain threshold depending on the vulnerability and exposure of people, buildings and infrastructure. The presented case studies include hydraulic stimulation designs from experiments at different scales of investigation from laboratory scale to field scale applications. Cyclic hydraulic fracturing tests on cubic granite samples were conducted in the laboratory using a true tri-axial test equipment combined with acoustic emission (AE) monitoring. A new advanced protocol of progressively increased cyclic injection and a pulsed injection design for hydraulic fracturing experiments was applied at the Hard Rock Laboratory in Äspö, Sweden. On field scale, a stimulation treatment was carried out in granodiorites at the EGS site in Pohang, Republic of Korea.