Hydraulic fracturing and microseismicity in granite and sandstone for EGS applications: a comparative approach

ABSTRACT: Hydraulic fracturing (HF) is applied in diverse geological settings, where the distinct properties of reservoir-rock formations can substantially influence the features of engineered fracture systems. In this study, we investigated the variations in HF processes in crystalline and sedimentary rocks through active and passive seismic monitoring. The study involved laboratory HF of Barre granite and Lyons sandstone cubes with combined active and passive seismic monitoring. Passive monitoring successfully mapped the generated HF, revealing a more tortuous HF for granite along with a higher number of microseismic events. The sensitivity of several active signals' attributes such as velocity and amplitude were significantly higher for the HF processes in granite compared to sandstone. The initial aseismic deformation and fluid leak-off were notably prominent in granite specimens. While the active signals' amplitude fluctuated for both granite and sandstone, the changes were significantly larger in granite. This suggests that HF induced intense alterations in the rock matrix and properties in granite. This study demonstrated that combined active and passive seismic analysis assisted in distinguishing HF processes between granite and sandstone. These findings can contribute to better comprehension of HF dynamic behavior, contributing towards improved control and efficiency of stimulation operations in geologically diverse environments.