Acoustic Emission Monitoring Of Rock Failure And The Mechanism Of Fracture-Network Generation

Tight reservoirs have ultra-low porosity and permeability,and complex fracture systems generated by volume fracturing are needed as oil and gas production channels.The formation of the hydraulic fracturing fracture network is controlled by many factors and its mechanism is complex,which needs further study.Acoustic emission is an elastic wave released by rock fracture,which has the capability of fracture location and fractures property identification.It is helpful to reveal the formation mechanism of the hydraulic fracturing network and evaluate the properties of artificial fractures.However,the low acoustic emission energy accompanying the hydraulic fracture propagation,the strong attenuation of elastic wave in rock,and the heterogeneity and anisotropy of the reservoir make the analysis of acoustic emission data very difficult.The application of acoustic emission in hydraulic fracturing experimental monitoring of tight reservoirs requires further development of acoustic emission detection and interpretation technology.Therefore,the combination of hydraulic fracturing simulation experiments and acoustic emission monitoring is of great significance for understanding the mechanism of rock fracture and fracture network formation in tight reservoirs and further evaluating the fracturing effect.The acoustic emission signal characteristics of rock fracture are analyzed,and a multi-channel acoustic emission monitoring hardware system with full waveform continuous recording is established.An acoustic emission data analysis method including full waveform feature analysis,multi-channel event location and fracture focal mechanism inversion is formed,which provides the experimental and theoretical basis for dynamic monitoring of fracture propagation.The acoustic emission monitoring experiment of tight rock fracture under uniaxial compression was carried out.Acoustic emission waveform parameters were used to characterize the rock fracture process,and the influence law of natural fracture on rock fracture was obtained.The real triaxial hydraulic fracturing acoustic emission monitoring experiment was carried out,and the fracturing results of Chang 7 group of tight sandstone,Lucaogou group of tight sandstone and Longmaxi group of shale were compared and studied,and the influence law of bedding property,fracturing fluid type and displacement on fracture propagation was obtained.Based on the interpretation results of acoustic emission monitoring data on the rock fracture process,the mechanical mechanism of formation of the tight reservoir fracture network under the action of fluid is analyzed.The acoustic emission parameters are combined with the discrete fracture network method to characterize the hydraulic fracturing network and evaluate the fracturing effect.This paper focuses on the core scientific problem of the formation mechanism of the artificial fracture network in tight reservoirs.Through the combination of hydraulic fracturing experiments and acoustic emission monitoring,the fracture process and properties of hydraulic fracturing rocks are analyzed,the mechanical mechanism of the formation of fluid-induced tensile and shear composite fracture network is revealed,the influencing factors and laws of the formation of fracture network are clarified,and the evaluation method of fracturing reconstruction effect combining acoustic emission parameters with discrete fracture network is proposed.