Study On The Effect Of Anisotropy Of Shale On Mechanical Properties And Strain Rate Effect

Shale gas is a new type of clean energy,which is widely distributed and rich in reserves,and has become a popular direction of global oil and gas exploration and development,and the mechanical characteristics of shale are the key factors affecting the overall exploitation of shale gas.However,there are few studies on the anisotropy and strain rate effect of shale.In this paper,uniaxial strain test,uniaxial compression test and three axial compression test are used to study the effects of shale anisotropy on mechanical properties and strain rate effects at different stratification planes.The contents are as follows:(1)The anisotropy of mechanical properties of shale is analyzed by single,three axial compression test and uniaxial strain test,the results show that the compressive strength,elastic modulus,Poisson’s ratio,failure mode,shale brittle extension,brittleness index,nominal pre consolidation pressure,lateral pressure coefficient characteristics with different angle of bedding surface shows different variation.The results of three axis experiments on shale were processed by SHANSEP method,and the relationship between OCR and normalized shear strength was established.(2)The damage softening constitutive model of rock based on Weibull distribution is established,and the stress-strain curve of three axial compression is analyzed.The results show that the constitutive model is better than that of the pre stress stage of the stress strain curve of shale,but it is not ideal for the post peak curve fitting.(3)Based on the shale under different confining pressures and strain rates of three axial compression test,investigate the mechanical properties of shale under different confining pressure and different strain rate.The results show that the confining pressures and strain rates affect obviously on elastic modulus,peak strength and fracture morphologies of the shale,the effects of low confining pressure and strain rate on mechanical properties of shale is obvious,with the confining pressure increasing,the strain rate effect of shale gradually weakened.