Investigation of acoustic emission response and fracture morphology of rock hydraulic fracturing under true triaxial stress

Hydraulic fracturing technique has been used to exploit hydrocarbons resources in the past years. To investigate the mechanism of hydrofracturing process, a true triaxial hydraulic fracturing device combined with acoustic emission (AE) system is employed to study the crack initiation and propagation under different injection rates. Furthermore, a 3D scanner is employed to obtain the morphology of the fractured surface when the fracturing test completes. The results show that in hydraulic fracturing, the cracks propagating mostly perpendicular to the direction of the minimum horizontal principal stress. A lower injection rate corresponds to the peak value of the AE count occurring at a later time and a large value of the cumulative AE count, indicating greater damage and a complicated crack propagation path. With the injection rate increased, the earlier the microcracks occur, the shorter the fracturing time of the specimen is, and the flatter the fracture morphology.