Monitoring of hydraulic fracture network by acoustic emission method in simulated tri-axial fracturing system of shale gas reservoirs

In the experiments to simulate hydraulic fracturing, monitoring and identification of the hydraulic fractures are fundamental to the study of the fracture morphology. Large scale hydraulic fracturing experiments were conducted using an indoor tri-axial physical simulation apparatus with 300 mm×300 mm×300 mm shale rock samples. A multi-channel acoustic emission monitoring system was applied, and the acoustic signals induced in the fracturing experiment were collected using acoustic sensors on the two sides of the sample to set up a 3D dynamic real-time monitoring system. The acoustic positioning technique can clearly recognize the initiation, orientation and morphology of the hydraulic fractures developed. Based on the data analysis of combined acoustic curve and pump pressure curve, the different stages of hydraulic fracture propagation can be monitored in real time, and the intercommunication between hydraulic fractures and natural fractures can be also recognized. The experimental results show that the peak point of the acoustic emission cumulative intensity appears prior to fracture pressure point and more signals are received during hydraulic fracture propagation comparison to the initiation of natural fracture. The fluctuation of pump pressure curve after fracturing can be used to recognize the interaction among fractures. The monitoring results of acoustic emission can be further verified by observing the tracer's distribution after breaking the rock sample. ©, 2015, University of Petroleum, China. All right reserved.