Hydrogen Damage Sensitivity Of Oil Well Tubes In Associated Gas Of Shale Oil

As a kind of unconventional oil and gas resources,shale oil resource has important development significance because of its rich resources,favorable characteristics and feasibility of development and utilization.However,the mining environment is in the harsh conditions of high temperature and high pressure containing hydrogen.When hydrogen enters into structural materials,it will cause the decrease of mechanical properties such as material plasticity,and oil well pipes will face the risk of hydrogen damage and failure.Therefore,the study of hydrogen diffusion behavior in oil well pipes plays an important role in improving the theory of hydrogen damage of materials.Meanwhile,in order to prevent hydrogen damage,the study of hydrogen barrier layer is of great significance in reducing the sensitivity of hydrogen damage of materials in hydrogen environment.In this paper,the aluminized steel and oxidized aluminized steel were prepared by solid powder embedding aluminizing process and oxidation annealing process with N80 casing steel as the matrix material.The microstructure and phase composition of aluminized layer and oxidized aluminized layer were analyzed by means of SEM,EDS and XRD.The results show that the surface of the aluminized layer prepared by embedded aluminizing has no cracks and pore defects.The average thickness of the aluminized layer is 290μm.The aluminized layer is composed of Fe₂Al₅and Fe Al,and the Al content decreases with the increase of the depth of the aluminized layer.The aluminized steel was oxidized at 900℃for 2 h,and there was no microscopic defect on the surface.Al₂O₃film was formed on the surface of aluminized layer,and the thickness of aluminized layer was 1μm.The average thickness of aluminized layer was 150μm.The infiltration layer is composed of Fe Al₂and Fe Al.Then,the diffusion behavior of hydrogen in different materials was studied by electrochemical hydrogen permeation technique,and hydrogen permeation kinetic parameters such as hydrogen diffusion coefficient and adsorption hydrogen concentration in different materials were analyzed.The hydrogen damage sensitivity index of materials under different conditions was studied by using environmental slow strain rate tensile test（SSRT）.The fracture mechanism of N80 steel,aluminized steel and oxidized aluminized steel under different conditions was investigated by fracture analysis.The results show that the steady-state current density of N80 is5.96×10^-6A·cm^-2,while that of N80 aluminized steel and N80 oxidized aluminized steel is significantly decreased,which are 2.24×10^-6A·cm^-2and 9.05×10^-7A·cm^-2,respectively.At the same time,the hydrogen damage coefficient of N80 steel is37.36%in the hydrogen environment at 25℃,and there is a great risk of hydrogen damage failure.The hydrogen damage coefficient of aluminized steel and oxidized aluminized steel is 20.31%and 14.97%,respectively,and no hydrogen damage occurs.At 350℃hydrogen environment,the hydrogen damage coefficient of N80 steel is as high as 43.98%,which is in the danger range of hydrogen damage failure,and serious hydrogen damage failure will occur.The hydrogen damage coefficient of aluminized steel and oxidized aluminized steel is 17.24%and 14.64%,respectively,and no hydrogen damage occurs.In order to study the mechanism of hydrogen barrier layer on the diffusion of hydrogen in the material,the method of galvanostatic electrochemical hydrogen charging was used to describe the N80 aluminized steel and diffused aluminized steel composite system by using Fick’s law under the condition of constant hydrogen concentration on the side of hydrogen charging.Through the corresponding boundary conditions and initial conditions,the boundary connection conditions are established by finite element difference method,and then the theoretical model of hydrogen permeation in aluminized steel system and oxidized aluminized steel system is established,and the actual diffusion coefficient and concentration distribution of hydrogen in aluminized steel and oxidized aluminized steel are obtained.