Multiscale Fracture Rupture Characteristic Study and Application of Sichuan Shale During Hydraulic Fracturing

Microseismic monitoring is a conventional technique used to evaluate the hydraulic fracturing effect according to the temporal and spatial distribution and evolution of located microseismic events (MEs) at the macroscale. It is generally thought that few or no located MEs reflects poor hydraulic fracturing results and that more located MEs indicate a better result, but the variability in rupture behavior at different rupture scales is ignored. This paper focuses on the characteristics of multiscale rupture of shale by combining laboratory acoustic emission and field microseismic monitoring. The results demonstrate that shear slippage along fractures mainly dominates the rupture behavior. If no pre-existing fracture is present at the microscale, in the laboratory experiment, a rupture mainly occurs along bedding planes, veins and cracks and predominantly slips, which can help develop a fracture network. Because seismic wave energy is related to the rupture scale and stronger MEs are generated by larger ruptures along pre-existing fractures, fault damage zones or isolated small faults, these slippages may cause casing deformation, and the connected fracture networks may result in fluid seepage. A large number of weak MEs are ignored during fracturing because too little energy is released from small ruptures to be effectively detected, but they usually indicate a fracture network and greatly contribute to gas production in the long term. Therefore, ruptures in shale generally occur from the microscale to macroscale and express similar rupture behavior at each scale but result in different seismic characteristics, located ME distributions, fracture evolutions and engineering effects.