Casing stress analysis with effects of temperature on material properties
In explociting heavy oil, hot steam is frequently injected into the well. The temperature of casing can reach up to over 300℃, which leads to remarkable change in material properties. The available safety analysis methods on casing did not involve these changes, and some models neglected the effects of formation, so the thermal stress in casing is mono-axial.All these simplifications led to large errors on casing yield condition and so casing failure rate is often high. By integrating casing, cement sheath and formation stone into a unified body, a tri-axial model on elastic thermal stresses was established with the effects of temperature on casing properties, such as Youngs modulus, yield stress and coefficient of thermal expansion considered. The incremental method was used to calculate the tri-axial thermal stresses in casing. Casing properties affect thermal stresses in casing apparently; the change of Youngs modulus reduces casing thermal stress slightly; the change of yield strength reduces yield stress and yield temperature; the change of thermal expansion coefficient has much more effects on thermal stress and yield temperature. The total effects make casing unsafe when temperature increment exceeds about 140℃; the function of tensile prestress is weakened by the temperature effects; higher grade steel casing does not have absolute advantage in tolerating high temperature. So, in order to reduce casing failures, casing properties, engineering technology and calculation methods are all required to be considered carefully.
Bao-kui Gao
Department of Oil and Gas Engineering, China University of Petroleum, Beijing 102200, China
国际会议
The 5th International Conference on Nonlinear Mechanics(第五届国际非线性力学会议)
上海
英文
397-402
2007-06-11（万方平台首次上网日期，不代表论文的发表时间）