弯曲井段套管抗挤强度理论及试验研究

Theoretical and Experimental Study on the Collapse Strength of Casing in Curved Well Section

为保证弯曲井段的套管抗挤强度满足作业要求,建立了弯曲载荷状态下的套管受力理论模型,结合ANSYS有限元模拟,研究了同规格套管的抗挤强度与井眼曲率之间的关系;同时建立了室内弯曲套管抗挤试验平台,进行了不同曲率下的套管抗挤试验。研究结果表明:抗挤强度与曲率服从良好的二次函数下降关系,在现场常用曲率范围内呈现线性下降趋势,当曲率继续增加,抗挤强度下降趋势越来越快,二次下降趋势明显;在钢级和尺寸相同条件下,套管壁厚越薄,抗挤强度受弯曲率影响越小,下降趋势越平缓;在每30 m井段曲率0°~7°范围内,有限元模拟、试验测试结果与理论计算结果相近,有限元模拟的最大误差为5. 57%,试验测试的误差最大为2. 91%。研究成果可为套管在弯曲井段的抗挤强度设计提供理论及试验参考。

To ensure that the collapse strength of casing in the curved section meets the operation requirements, the theoretical model of force on casing under bending load is established. Combined with ANSYS finite element simulation, the relationship between collapse strength and borehole curvature is studied. The indoor bending casing collapse test platform is established to conduct casing collapse test under different curvatures. The results show that the collapse strength and the curvature is in a good quadratic function decreasing relationship. A linear decreasing is observed under the curvature range commonly used on site. When the curvature increases, the collapse strength decreases more and more rapidly, and the quadratic function decreasing trend is becoming dominated. Given the same steel grade and casing diameter, the collapsed strength of thinner casing wall thickness would be subject to smaller influence of curving rate, present gentler decreasing trend. In the curvature range commonly, the finite element simulation and indoor test are similar to the theoretical calculation results. The maximum error of the finite element simulation and the indoor test is 5.57% and 2. 91%, respectively. The research results provide a theoretical and experimental reference for the design of the casing in the curved section.