Mechanical Behavior And Acoustic Emission Time-Frequency-Space Characteristics Of Shale Fractured By High-Pressure Fluid

Low porosity and poor permeability of shale reservoir have been restricting the industrial development of shale gas resources.For shale gas exploitation,waterless fracturing technology not only has a very good fracturing effect,but also can reduce the waste of water resources and avoid fracturing fluid pollution to the environment.As a simple and controllable construction parameter,the viscosity of fracturing fluid affects the development efficiency of shale gas to a large extent,so it is of great significance to carry out research on it.Therefore,it is of great research and engineering significance to compare the fracture initiation,expansion,penetration and failure evolution laws of shale injected with different media,and analyze the time-frequence-space characteristics of AE signals in the fracturing process,which is of great significance to the selection of fracturing fluid in the industrial development of shale gas resources.Taking concrete samples to simulate shale as the research object,this thesis independently developed a large-size true triaxial coal rock mass multi-field and multi-phase fracturing experimental device,studied the fracturing pressure-time relationship during high-pressure fluid injection fracturing,the time-frequency-spatial characteristics of acoustic emission signals,the fracture morphology and fracture network distribution of samples after fracturing,and revealed the failure mechanism of shale fractured by different high-pressure fluid injection.The main research achievements are as follows:(1)The large size true triaxial coal rock mass multi-field and multi-phase fracturing test device is developed,the specific structure of the device is designed,the technical parameters of the device are determined,the main functions of the device are described,the use method and test flow of the device are formulated,and the significant characteristics and advantages of the device are summarized.(2)The evolution law of fracturing pressure with time in the process of fracturing rock with different media injected is studied,the difference of sensitivity of fracturing pressure change in high-pressure fluid injection fracturing test under different working conditions is analyzed,and the influence of injection media,horizontal stress difference and vertical stress on fracture morphology and fracture network complexity after pressure is clarified.The differences and similarities of internal damage characteristics of reservoir shale fractured by gas medium injection are discussed.The mechanical behavior and fracture development mechanism of high pressure fluid injection fracturing reservoir shale are revealed.(3)The time-domain characteristics of AE signals in different stages of high-pressure fluid injection fracturing are expounded,the evolution law of AE ringing count,b value,β_t value and RA-AF in the fracturing process is studied,the number,size,type and other key information of fracturing failure events are deduced,and the internal failure process of fracturing reservoir shale and the cracking mechanism of different high-pressure fluids are revealed.(4)The frequency domain law and spatial relationship of AE signals induced by different medium injection are discussed,the frequency domain parameters of AE signals and the spatial aggregation characteristics of failure events are analyzed,the AE spectrum diagram,the dominant frequency and its amplitude,the spatial location of failure events and the evolution law of energy release are studied,and the deep difference in failure mechanism of rock mass fractured by different medium injection is expounded.There are 77 figures,6 tables and 78 references in this thesis.