Investigating the Propagation of Multiple Hydraulic Fractures in Shale Oil Rocks Using Acoustic Emission

The propagation of multiple fractures plays a significant role in the effectiveness of hydraulic stimulation in shale oil reservoirs. Previous studies reported that the laminations and bedding interface in shale oil rocks could influence the propagation of single hydraulic fracture. However, the propagation mechanism of multiple fractures in such rocks is still unclear. Here we use a true-triaxial experimental system, together with the acoustic emission (AE) monitoring system, to investigate the propagation of multiple fractures in shale oil reservoir rocks. The results show that the fracture interference started at the initiation stage seriously affects the propagation of multiple fractures. More clusters per stage could aggravate the fracture interference near the wellhead. The laminations and bedding interfaces are the main causes of fracture interference and could hinder the height of hydraulic fractures. Shear-type AE event signals the generation of fracture interference caused by the slip of bedding interface and the deflection of fractures induced by the laminations. The mechanism of fracture interference not only lies in stress shadow but also in the changes in fluid pressure caused by the high permeability of laminations and bedding interface. The experimental results provide basic and detailed data for studying hydraulic fracturing in shale oil reservoirs.