考虑弯矩和剪切影响的造斜段套管抗挤强度分析

Analysis of Collapsing Strength of Casing in Buildup Section Considering Bending Moment and Shear Influence

水平井造斜段套管受弯曲、剪切和挤压等载荷共同作用,受力条件复杂多变,常发生错断或挤毁等安全事故。为此,根据水平井造斜段套管井眼轨迹的几何特性,考虑弯曲、剪切和挤压联合作用,建立造斜段套管力学模型,应用拉梅厚壁筒理论和第四强度理论,导出水平井造斜段套管抗挤强度公式。应用公式计算了不同井眼曲率、不同壁厚2种套管的抗挤强度,并进行了ANSYS有限元验证。分析结果表明:每25 m井眼曲率由3.75°增加到15.00°,P110套管的抗挤强度下降约53%,TP140套管的抗挤强度下降约28%;每25 m井眼曲率为3.75°时,φ139.7mm×12.7 mm P110套管的抗挤强度为89.8 MPa,比φ139.7 mm×10.54 mm P110套管大27%。随着井眼曲率的增加,弯曲套管的抗挤强度降低明显。研究结果可为提高水平井造斜段套管的安全性提供参考。

Casings in buildup section of horizontal wells are prone to safety accidents like rupture or collapse under the joint effect of bending, shear and extrusion load. In view of this, a mechanical model of casing in the buildup section is established according to geometrical features of wellbore track and taking into account of the joint effect of bending, shear and extrusion. The formula of collapsing strength of the casing in buildup section of hori-zontal well is derived by using Lame thick-walled cylinder theory and the fourth strength theory. Collapsing strength of two casings with different wellbore curvature and wall thickness is calculated with the formula and performed with ANSYS finite element verification. The result of analysis indicates that when wellbore curvature increases from 3. 75.to 15. 00.per 25 m, collapsing strength of P 110 casing reduces by 53 % approximately and that of TP140 casing reduces by 28% approximately. And when the wellbore curvature is 3. 75.per 25 m,collapsing strength of 0139. 7 mm ×12. 7 mm P 110 casing is 89. 8 MPa, 27 % higher than that of 0139. 7 mm× 10. 54 mm P 110 casing. With the increasing of wellbore curvature, collapsing strength of the casing in the curved section reduces sub-stantially. The research result provides a reference to the safety of the casings in buildup section of horizontal wells.