Study On The Evolution Characteristics And Model Of Strength Parameters And Dilation Angle Of Layered Shale

Energy is the driving force of social development and an important guarantee for the sustainable development of national economy.With the enhancement of people's awareness of environmental protection and the increasingly serious shortage of domestic energy resources,the demand for clean energy in China is increasing gradually.Based on the analysis of the global non-renewable energy exploration and development status,it is found that shale gas is one of the most realistic replacement resources for conventional oil and gas resources.In order to obtain the mechanical characteristics of shale to realize the exploitation of shale gas,scholars have carried out a large number of laboratory tests on shale and achieved a series of research results.However,shale oil and gas development is relatively short,in the existing studies,there are few studies on the evolution characteristics of strength parameters(cohesion and internal friction angle)and dilation angle of layered shale,and on the basis of which the relevant models are established.Therefore,on the basis of a large number of shale uniaxial and triaxial compression test results,the constitutive relations of strength parameters and deformation parameters applicable to shale are constructed in this paper,Which provides theoretical guidance for the establishment of shale gas reservoir model and numerical simulation calculation of subsequent exploitation and provides reference for the study of mechanical properties of other layered rocks.The main work content and research results of this paper are as follows:(1)Based on the uniaxial and triaxial compression test results of 111 shale specimens,the evolution law of cohesion and internal friction angle with plastic shear strain was calculated:With the increase of plastic shear strain,the cohesion of shale decreases monotonously,and the internal friction angle increases first and then remains unchanged.A strength parameter evolution model of layered shale has been established,and the model parameters have clear physical significance.Further study on the model parameters shows that the angle of shale bedding has a significant effect on the model parameters,that is,the anisotropy of shale significantly affects the evolution process of shale strength parameters.(2)Based on the triaxial compression test results of 63 shale specimens,the evolution law of dilation angle with plastic shear strain of layered shale is obtained:When the dip angle of shale is between 30°and 60°,the dilation angle tends to increase first and then stabilize.When the shale dip angle is not in the range of 30°-60°,the dilation angle tends to increase first and then decrease.Shale anisotropy is an important factor affecting the evolution of shale dilation angle.A simplified dilation angle model of layered shale is established,which can express the effects of bedding angle and confining pressure on the dilation angle of shale.(3)Using the built-in FISH language of FLAC^3D software,the strength parameter evolution model and the simplified dilation angle model were embedded into the numerical calculation process of shale triaxial compression test,and the total stress-strain curve in the compression failure process of shale was predicted.The fitting results are in good agreement with the actual triaxial compression test results,which verifies the applicability of the proposed model.