Dynamic response of thick-walled casing in oilfield's ultra deep well under kinetic inside pressure and experimental validation

Introducing the intermediate principal stress coefficient and tensile-to-compressive strength ratio, the analytical solutions for elastic and plastic ultimate inside pressures in thick-walled casing respectively with two closed ends, two open ends and plane strain under kinetic inside pressure are obtained using the unified strength theory. Plastic flow first occurs on inside wall of the thick-walled casing, and is restricted by the surrounding elastic material. Numerical emulation displays that the elastic ultimate inside pressure adds as the tensile-to-compressive strength ratio decreases and the intermediate principal stress coefficient enhances. The value of the elastic ultimate inside pressure for the thick-walled casing with two closed ends is largest, followed by value for the plane strain one, and value for one with two open ends is minimal. The interfacial critical radius becomes larger due to the increase of the kinetic inside pressure. If the kinetic inside pressure ascends, the thick-walled casing diverts from elastic deformation to elastoplastic deformation and the interfacial critical radius expands from inside radius to outside radius. The plastic ultimate inside pressure gains as the tensile-to-compressive strength ratio reduces. The differences among the plastic ultimate inside pressures of thick-walled casings with two closed ends, two open ends and plane strain become smaller with the increment of the outside-to-inside diameter ratio for the equivalent unified strength theory parameters. The elastic ultimate inside pressure is lower than plastic ultimate's. The relative error between theoretical values and test data for plastic ultimate inside pressure is between -3%~-9%. The relative warp between international standardization organization's template data and test data is between -12%~-25%. The relative windage between American petroleum institute's average lines and test data is between -16%~-33%. Comparisons show that the current plastic ultimate inside pressure's equation in thick-walled casing is closer to test data. © 2018, Nanjing Univ. of Aeronautics an Astronautics. All right reserved.