Study On The Static And Dynamic Damage Constitutive Model Of Bedding Shale

Shale reservoirs will be damaged and ruptured under the interference of artificial fracturing and penetration enhancement,which greatly improves the permeability of shale gas,thereby improving the efficiency of shale gas recovery.The stope shale reservoir has also experienced the process of original rock,damage development,and fracture.The corresponding rock mechanical properties of each stage have undergone great changes.At this time,the traditional rock mechanics constitutive theory cannot accurately describe its damage.To develop the mechanical behavior in the whole process,it is necessary to construct a new static and dynamic damage constitutive model.In this paper,through laboratory experiments,theoretical derivation and numerical simulation,the damage constitutive theory of bedding shale under static and dynamic loads is established,and the damage and permeability evolution laws of shale reservoirs around industrial fracture troughs are established.Conducted research,the main contents are as follows:(1)Single and three-dimensional compression tests were carried out on shale samples with different bedding dip angles.The results show that the peak strength and elastic modulus of the shale sample decrease first and then increase with the increase of the inclination angle of the inner bedding surface of the rock sample.When the inclination angle is 50,the compressive resistance is the weakest.This is due to the inclination angle of 50,the bedding surface is close to the shear failure surface of the rock under three-way compression,and the sample is prone to shear failure along the bedding surface.In addition,the greater the confining pressure is applied,the greater the peak strength and elastic modulus of the shale.(2)Based on the results of compression tests,the damage variable was defined by introducing plastic strain,and the damage evolution equation of rock material was established.Based on the D-P strength criterion,an elastoplastic damage constitutive model and strength criterion are constructed,and a numerical integration algorithm is derived to solve this equation.On the basis of theory,using FORTRAN language to compile the finite element program,the compression test process of bedding shale was numerically simulated,and the test results were compared and analyzed.The results show that the elastoplastic damage constitutive model established in this paper can better reflect the stress and strain changes of bedding shale before and after the peak.(3)Impact loading tests were carried out on shale samples with different bedding dip angles,and the mechanical properties and failure characteristics of bedding shale in dynamic tests were analyzed.The results show that the bedding dip angles have obvious effects on the mechanical properties of shale in the dynamic tests.Less than the static load test.At this time,the loading strain rate plays a major role in the mechanical properties and failure characteristics of the shale.The higher the loading strain rate,the greater the compressive strength and elastic modulus,the greater the fracture degree,and the smaller the effect of the bedding dip.(4)Based on the impact test results,the damage variables related to the loading strain rate and strain are introduced,the damage evolution equation is established,and a dynamic damage constitutive model suitable for bedding shale is constructed.The FORTRAN language was used to develop the finite element source program,a subroutine to solve the dynamic damage constitutive equation was compiled,and the impact test process of bedding shale was numerically simulated.The calculation results show that the calculation results of the finite element program developed based on the dynamic damage constitutive model can better reflect the dynamic mechanical characteristics of bedding shale during impact loading.(5)Using the damage finite element program,the damage field and the distribution and evolution of the permeability of the shale reservoir around a fractured slot are calculated and analyzed.The results show that as the pressure on the slot increases,the surrounding area of the slot The degree of damage and the scope of damage to shale reservoirs have also continued to expand,so that the permeability of shale reservoirs has been greatly improved.With the continuous rupture of the shale in the large damage area,the pressure boundary of the fracture and groove is also moving forward,and the pressure relief range is increasing.This Thesis includes 77 figures,11 tables and cites 94 references.