Cyclic soft stimulation (CSS): a new fluid injection protocol and traffic light system to mitigate seismic risks of hydraulic stimulation treatments

Hydraulic stimulation treatments are standard techniques to access geologic resources which cannot economically be exploited with conventional methods. Fluid injection into unproductive formations may increase their permeability by forming new fractures and activating existing ones. A major risk of this process is a possible occurrence of seismic events that can potentially be felt on the surface or even cause minor damage. In this paper, an advanced fluid injection scheme is proposed that aims to mitigate these unwanted events and to improve the permeability enhancement process. Amongst other procedures, it involves different types of cyclic injection and a traffic light system specifically designed for cyclic injection schemes. The concept is applied to develop a stimulation design for the Pohang enhanced geothermal system site in Korea, where it was first deployed in the field in August 2017.Hannes Hofmann was funded by the European Unions Horizon 2020 research and innovation programme under Grant agreement No. 691728 (DESTRESS). Ki-Bok Min was funded by the Korea–EU Joint Research Support Program of the National Research Foundation of Korea (NRF) through a Grant (No. NRF-2015K1A3A7A03074226) funded by the Korean Governments Ministry of Science and ICT