A Study Of The Reason For Casing Corrosion In The Asp Flooding And The Critical Residual Wall Thickness

In the process of oil exploitation, the casing is the important exchange channel between the ground and the underground. Due to a variety of flooding oil making the produced fluid composition complex, casing service conditions are very harsh. And the physicochemical environment complexity makes the casing failure phenomenon occur frequently.It brings great influence to the safety of oil field production.In this paper, according to the actual production of Daqing oilfield, the corrosion casing failure analysis of the three element compound flooding wells is carried out. Through the macro analysis and micro analysis of the failure tube, the corrosion is mainly on the inner wall, and the adhesion has thicker scale, and a lot of corrosion pits formed under the adhesion. Severe localized corrosion, especially the corrosion under the adhesion, is the main cause of casing failure. Through the analysis of the electrical conductivity, pH value and chemical composition of the corrosion medium, we find that the anti- scale agent and acid- cleaning solution can accelerate the corrosion process. Ultimately the corrosion mechanism of casing is determined. In the early stage, oxygen corrosion occurred, and in the process of corrosion, the corrosion under the adhesion maked the tube perforated. In the process of corrosion, the H+, Cl- and the anti- scale agent directly accelerated the corrosion.Combined with the failure mechanism of corrosion and the mode of the local corrosion,by using ANSYS finite element software, we can simulate how the geometrical size of flat square, flat oblong, elliptic, circular etch pits and combined corrosion defects and internal pressure effect on the failure. we can find out the corrosion depth and pressure have the greatest impact than the defect length and width. For the circular pitting pit, when the depth is over 7mm, the equivalent stress maximum will appear obviously.For the double point corrosion, the thesis simulates the flat square and oblong corrosion defects, and mutual interference distance of the two kinds of defects are 90 mm and 115 mm respectively. In addition, by containing corrosion defects casing indoor simulated pressure experiment, experimental data and ANSYS software simulation data are compared, which Complies with the requirements of less than 10% in engineering application.that can prove the accuracy of the finite element analysis method. Finally, combined with the the optimization design module of ANSYS Workbench software, secondary development is carried out, and it make calculation of casing corrosion critical residual wall thickness, more convenient, also lay the foundation for the prediction of residual life.