(1. SINOPEC Research Institute of Petroleum Engineering，Beijing 100101，China；2. State Key Laboratory of Shale Oil and Gas Enrichment Mechanisms and Effective Development，Beijing 100101，China；3. State Key Laboratory of Geomechanics and Geomechnical Engineering，Institute of Rock and Soil Mechanics，Chinese Academy of Sciences，Wuhan，Hubei 430071，
China；4. University of Chinese Academy of Sciences，Beijing 100049，China)
Abstract：Aiming at the condition of high horizontal stress difference in deep shale(greater than 10 MPa)，in order to clarify the formation law of complex fracture network in deep shale layers and to explore the stimulation methods to improve the complexity of fracture network，three fracturing modes were designed including gradually increasing the pumping rate in a pulsed style，step-form increasing the pumping rate and maintaining a constant pumping rate. By means of a large hydraulic fracturing apparatus under true triaxial condition，acoustic emission monitoring system and dissection photos of samples，the crack modes and extension rules of hydraulic fractures in deep shale were analyzed. The experimental results show that to some extent the total volume of injected fracturing fluid can reflect the complexity of fractures，and the more the total volume，the more complex the fracture net. For the fracturing mode with a pulsed pumping rate，the pump-stopping period contributes to the infiltration of the fracturing fluid into natural cracks and hence to activate natural fractures. The pumping rate of the fracturing fluid has a great impact on the formation of the complex fracture network，and a small pumping rate is conducive to the opening of original natural fractures while a high pumping rate makes the hydraulic fracture directly cut cross the pre-existing natural fractures. It is very important to open the natural fractures which are the material basis for forming the complex fracture net. The experimental study can provide a reference for on-site fracturing design.
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2019, Vol. 38 
