Numerical Simulation Of Crack Propagation In Surrounding Rock Of Shaft Wall Of Expanded Finite Element Mud Shale

With the large-scale exploration and development of mud shale gas wells,researchers at home and abroad have attached great importance to the problem of stability of mud shale wellbore and have been working on this issue.However,with in-depth study of the problem of wellbore stability,the researchers found that the cause of the ultimate macroscopic fracture of the rock is related to its internal microstructure and micro-defects.Therefore,it is indispensable to study micro-cracks and micro-defects in the surrounding rock of mud shale wellbore.In this paper,the following research contents are carried out for the surrounding rock of mud shale shaft wall:(1)Through experiments on the core of the oil well shale interval in a block in Xifeng Oilfield,it is concluded that the changes in the well wall after fluid shale shale wall are mainly caused by illite,montmorillonite,kaolinite and green.The mudstone shale ion exchange capacity and specific surface area are positively correlated with the hydration reaction degree of the shale clay mineral.(2)The triaxial strength experiment is performed indoors on the core sample to obtain the rock mechanics parameters of the target interval and determine the range values of the rock mechanics parameters.Through experiments,it can be concluded that the heterogeneity and anisotropy of the rock sample are obviously caused by different coring directions,which will cause changes in rock elastic modulus,Poisson's ratio and compressive strength parameters.(3)The finite element crack propagation model of wellbore compression is established by ABAQUS.The well wall contains a finite element model of the crack and a three-dimensional crack propagation model under horizontal ground stress.The effects of Young's modulus,Poisson's ratio,drilling fluid and porosity on the micro-cracks and micro-defects of the borehole wall were studied by numerical simulation from the parameters of rock mechanics,rock fracture strength and ground stress.The results show that the crack propagation and trend and the length and width of the crack are affected by the minimum horizontal stress,drilling fluid performance,pore pressure and working time.