Comparison of cyclic and constant fluid injection in granitic rock at different scales

摘要

Exploitation of unconventional energy resources often requires fluid injection to improve the hydraulic performance of the reservoir. A potential risk associated with these hydraulic stimulation treatments is the unintended development of manmade seismic events. Therefore, mitigation measures for seismic risks associated with fluid injection is of major importance for many applications, such as shale gas, tight oil and enhanced geothermal systems (EGS). As part of a portfolio of options, cyclic injection schemes were recently proposed to reduce the risk of inducing larger seismic events. To prove this concept, a series of experiments with cyclic and constant fluid injection rates were performed in granitic rocks at laboratory scale (Pocheon Granite), at mine scale (-spo Hard Rock Laboratory, Sweden) and at field scale (Pohang EGS site, Korea). All experiments have in common that the hydraulic performance could be improved with lower magnitude seismic events and lower breakdown pressure, thus showing the potential to mitigate seismic risk of hydraulic stimulation treatments.