Hydraulic conductivity of the crystalline crust: Insights from hydraulic stimulation and induced seismicity of an enhanced geothermal system pilot reservoir at 6 km depth, Espoo, southern Finland

•St1 deep heat project, Finland, the world's deepest EGS pilot reservoir.•Hydraulic conductivity of crystalline rocks was measured at 5 – 6 km depth.•Natural level of conductivity before stimulation 5 0·10−10 – 5 0·10−9 m/s.•Hydraulic stimulation improved conductivity temporarily by two orders of magnitude.•Stimulation generated >80,000 micro-earthquakes in five clusters.