超深水完井工况水下卧式采油树结构强度评估

Assessment on Structural Strength of the Subsea Horizontal Tree in Ultra-deepwater Completion

水下采油树作为深水完井作业的关键设备,其可靠性对深水完井作业的顺利实施有很大影响。在建立隔水管-采油树-井口-导管系统有限元模型的基础上,分析了水下采油树局部受力模型,提出了完井工况下采油树结构强度评估方法和流程,识别强度弱点部位,同时分析了作业船偏移、水深和油管长度对水下采油树应力特性的影响规律。分析结果表明,水下采油树主要受力部位为采油树主体圆筒,进、出油管道受力较小,采油树最大等效应力出现在树体上部圆筒凹槽处;水深2 500 m、作业船偏移5%时采油树等效应力710.7 MPa,接近其材料屈服强度785.0MPa;弯矩方向对采油树受力影响较大,随着弯矩方向与采油树进、出油孔道轴线的夹角在0°~360°之间变化,采油树最大等效应力变化幅度达43%。

The subsea tree is a key device for deepwater completion operations. Its reliability has a great influ- ence on the implementation of deepwater completion. The finite element model of riser-subsea tree-wellhead-conduc- tor system is established. The subsea tree local mechanical model has been analyzed. The structural strength assess- ment methods and procedures for subsea tree are proposed, and the method to identify the weak point is intro- duced. The effect of the ship offset, water depth and tubing length on the subsea tree stress characteristics are ana- lyzed. The resuhs show that the main forced area of subsea tree is the main body cylinder. The inlet and outlet pipe have smaller stresses. The maximum equivalent stress of the subsea tree appears on the cylinder gap of the upper subsea tree. The equivalent stress of the subsea tree is 710.7 MPa under the water depth of 2 500 m and the ship offset of 5% , which is close to the material yield strength of 785.0 MPa. The bending moment direction has a grea- ter impact on the stress of subsea tree. Within the angle range of 0° - 360° between the bending moment direction and the axis of the flow pass of subsea tree, the variation of the maximum stress of subsea tree is up to 43%.