Api Casing Collapse Pressure Calculation Formula Applicability Study

The paper describes the development and ressarch overview of the calculation of casing collapsing intensity in China and abroad which is based on a large number of research on literature, with the development of deep and ultra-deep wells and heavy oil thermal production wells, combined with the current deep and ultra-deep in the tube and underground damage situation and the actual temperature field environment, analyzed the importance effects of the temperature on the collapse intensity of casing.Based on the existing casing intensity design methods,considering the factors including the temperature,proposed the new ideas of using API casing resisting collapsing pressure formula to design casing resisting collapsing intensity.The paper deeply analysis that the temperature impact on the material properties and microstructure by the deep research of plastic deformation of metal materials, the yield theory and temperature deformation processing theory. Combined with the actual well temperature field environment, design a testing program.we do the research of material properties selected 25℃,100℃,150℃,200℃,300℃five temperature points in the well temperature field.We do the dynamic tensile data test for material J55 steel at different temperature environments.The results show that, J55 yield intensity with increasing temperature present overall downward trend.Through the API casing collapsing theoretical research, the paper proposed the calculation new ideas. Although the API casing collapsing theory has been widely used, but the theory is established at room temperature environment, we don't know whether using in well temperature environment is reliable or not, we use FEM to test and verify the theory. Based on experimental data, namely using the API casing collapse pressure intensity calculation formula and finite element analysis method to calculate the casing collapsing intensity in under-well temperature field and the results were compared.The comparative results show that:1) the reliability of using the method of finite element analysis program; 2) the existing API analysis methods of casing collapsing intensity does not match the actual casing collapsing intensity in the well temperature environment,even vary widely, in the range of under-well temperature field, the difference between minimum and collapsing intensity in normal temperature is 10% or more; 3) The new idea of calculation results get the same change trend with actual casing collapsing intensity in the well temperature field environment. but some deviations still exist with the actual casing collapsing intensity and there are still, and the gap between them presents increasing trend with the temperature rising, but it is not a major impact; 4) The application of the API casing collapsing formula in the welltemperature field environment has a certain reliability for the J55 casing.