高温高压超深气井油管柱屈曲行为研究

对于超深、高温、高压以及高产等复杂工况的气井,前人推导的管柱屈曲行为经典理论公式无法完整或准确地描述油管柱底部非均匀或非完整的正弦屈曲或螺旋屈曲形态。为此,采用ANSYS软件,建立了超深井全井筒油管柱屈曲行为分析的有限元力学模型,并以塔里木油田某超深井为例,针对管柱屈曲行为开展了油管柱屈曲形态与其横向位移、油管—套管接触压力分析。结果表明:(1)所建立的高温高压深井超深井油管柱屈曲分析有限元模型可以对油管柱屈曲形态进行全井段分析,复杂力学工况下的油管柱中和点到封隔器处的油管柱处于非均匀或非完整的正弦屈曲或螺旋屈曲;(2)油管柱底部轴向压力为205 k N时,油管柱接触段的顶部和底部分别发生正弦屈曲、螺旋屈曲自锁现象,该自锁现象可能导致油管柱处于永久性的屈曲状态。结论认为,所建立的模型可用于分析油管—套管屈曲过程中的屈曲形态、接触压力及其摩擦力,为油管柱屈曲形态、摩擦损伤失效分析及预防措施制定等提供了方法和依据。还提出了延长管柱使用寿命的措施建议:油管柱坐封前在井口施加适当的提拉力、增加底部油管柱结构尺寸、提高井口油压或适当降低产量等。

Buckling behaviors of tubing strings in HTHP ultra-deep wells

Classical theoretical formulas for the buckling of pipe strings derived by previous researchers may not completely and accurately describe the non-uniform or incomplete sinusoidal buckling or helical buckling forms around the bottom of tubing strings in HTHP ultra-deep gas wells. In this paper, a finite element mechanical model for analyzing the buckling behaviors of tubing strings in HTHP ultra-deep wells was established by using the software ANSYS. With an ultra-deep well in the Tarim Oilfield as an example, systematic analyses were conducted on the buckling of tubing strings with regard to buckling configuration, horizontal displacement, tubing–casing contact pressure. The results are revealed in two aspects. First, the proposed finite element analysis model for the buckling behaviors of tubing strings in HTHP ultra-deep wells can be used to highlight buckling configurations throughout the entire hole. It can be seen that the interval between the central point and the packer under complicated mechanical conditions is in inhomogeneous, or incomplete sinusoidal or helical buckling forms. Second, in such cases with an axial pressure of 205 kN at the bottom of the tubing string, the contact sections at the top and bottom of the string may experience self-locking due to sinusoidal and helical buckling, respectively. The self-locking phenomenon may lead to permanent buckling of such strings. In conclusion, the proposed model can be used to highlight buckling configurations, contact pressures and frictions during tubing–casing buckling. The model provides a reliable technique and foundation for analyses related to buckling configurations, friction damages, failures and relevant prevention measures. To prolong the service life of tubing strings, it is necessary to apply suitable lifting forces, enlarge the dimensions of tubing strings at bottom, promote wellhead pressures or properly reduce productivities.