Numerical Simulation Study On Crack Propagation Mode Under Shale Deflagration Fracturing

As a waterless fracturing technology,deflagration fracturing can form multiple radial cracks around the shale reservoir to realize the reconstruction of the shale reservoir,which is conducive to the efficient development of shale gas in China.For shale gas reservoirs with high brittle mineral content,strong heterogeneity and natural fracture development,combined with the characteristics of deflagration fracturing technology,this study is based on outdoor experiments and numerical simulations to explore the crack propagation law of shale gas deflagration.It is proposed to use shale in the Sichuan Basin as the research object.Based on the reference of the previous research results,based on the Hopkinson bar compression test,the relevant mechanical parameters of the shale can be obtained and then we can get the appropriate shale mechanical model parameters according to the stress and strain curves obtained from the test.Therefore,using the simulated shale expansion mode of deflagration fracture under different conditions of gunpowder and multi-stage initiation.The main factors affecting the shale crack propagation mode are analyzed,which provides a theoretical basis for improving the single-shale shale gas production.The main contents are as follows:(1)Through the Hopkinson rod compression experiment of shale at normal temperature,60°C,90°C,120°C,150°C five groups,0.2MPa,0,3MPa,0.4MPa three groups of air pressure,The stress-strain curves of shale at the same pressure,different temperatures,and the same temperature and different pressures were obtained.The CT scanning experiment of shale shows that the compactness of shale is better,but there will be natural cracks.(2)The appropriate shale mechanics model is selected in the LS-DYNA software.Verify the model parameters and the applicability and rationality of the selected model according to shale Hopkinson compression test results.(3)Based on the validated model parameters,LS-DYNA numerical simulation was used to investigate the influence of different propellant quantity and multi-stage pulse on fracture propagation under shale deflagration fracturing.The higher the amount of gunpowder,the faster the crack grows,but only by selecting the appropriate amount of gunpowder can the crack expansion network be more reasonable and not to destroy the shale storage due to excessive peak pressure;By means of multi-stage initiation,the fracture propagation model of shale reservoir can meet the needs of mining as much as possible;A single point detonation can produce longer cracks and more radial cracks than simultaneous multi-point detonation.The results of this paper can provide relevant guidance for the design,parameter control and optimization of horizontal well deflagration fracturing in shale gas reservoirs,and have important theoretical value.