Research On Environmental Fracture Simulation Of High-strength Tubing And Casing Steel Based On Mesomechanics

The oil casing is used to support the oil and gas well wall steel pipe to ensure the normal operation of the whole well after the drilling process and completion.Due to the different geological conditions,the underground stress state is complicated,and once the casing itself is damaged for some reason,it may result in the production loss of the whole well,or even scrap.With the increase of deep well and super-deep well and the environment of H2S,the failure of oil casing is frequent,which puts forward higher requirements for oil casing.The macroscopic properties of the oil casing are closely related to the mechanical properties under the microscopic scale.On this basis,the method of macro-scale and meso-scale should be combinated to analysis the oil casing failure causes and the deformation and failure mechanism in deep level.From the macroscopic and mesoscopic angles of study on fracture mechanism of steel,a lot of research and related literature at home and abroad are researched in this paper,and on the basis of mesoscopic mechanics analysis method I analysis micromechanical finite element model which contain defects(micro cracks and inclusions).The stress and strain distribution of material mesoscopic scale which contains the defects and its influence on macroscopic properties are analysised under different load.The extended finite element method(XFEM)was adopted to analysis the meso-scale model containned micro cracks.Analysising the dynamic crack extension process and the stress and strain distribution,a new method for exploring oil casing failure mechanism are provided.The main results of this paper are as follows:(1)The high strength steel tensile mechanical properties of experimental study are developped,and the results provides the basis to the material parameter selection,what'more the fracture microstructure analysis was carried out to get the material of the micro cracks and inclusions size and distribution.High strength steel hydrogen and SSC experiment was carried out,and I observe the fracture microstructure on corrosive environment.Finally the macroscopic mechanical properties,measured mesoscopic structure and size in acidic conditions are getted which provides the basis for modeling.(2)According to the theory of material mesoscopic mechanics,the representative volume unit RVE micromechanical finite element model of high strength steel containing micro cracks is established,to analysis the micro crack length and angle of modeling;The finite element model of microcrack containing hydrogen pressure and non-hydrogenation pressure was compared and analyzed.The stress distribution of multiple microcracks was analyzed,and the results were treated uniformly,and the response of microcracks and hydrogen pressure to the macroscopic properties of the oil casing materials was studied.(3)The finite element model of the representative volume element RVE of high strength steel which contains inclusion was established,and the inclusion shape was modeled and analyzed.The response to the macroscopic properties of the materials is analyzed.(4)Based on extended finite element theory and fracture mechanics theory,I establish the finite element model of mesoscopic extension which contains micro cracks.ABAQUS is used to simulate the process of crack propagation and fracture,and the stress and strain distribution of the micro cracks under the dynamic extension are analysised,then the results are taken into homogenization processing to analysis the reponse of micro crack propagation on the properties of oil casing material macroscopic.