隔水管顶张力对水下井口系统稳定性影响

Influence of the top tension of riser on the stability of subsea wellhead system

海洋深水钻井过程中,隔水管张力器系统提供恒定的顶张力调节隔水管的受力和形变,是保证水下井口系统稳定的关键。综合考虑海流、平台偏移、海底土、顶张力等影响,建立了水下井口系统力学分析模型及水下井口挠曲微分方程,基于理论模型分析了不同顶张力下(张力比:0.9、1.0、1.1、1.2、1.5)隔水管系统的弯矩和横向位移特征,采用力学等效转化的方法,分析了顶张力大小对水下井口稳定性的影响特征。结果显示,水下井口安装到位后,在平台偏移量固定的情况下,轴向载荷顶张力是影响井口稳定的唯一可控因素;提高隔水管顶部张紧力,可以进一步改善隔水管和水下井口的变形和受力状况,在深水现场钻井作业中,基于最小顶张力计算方法,设置1.0~1.5倍张力比有利于提高水下井口系统的稳定性。

In the drilling process in deep water,the tenser system of the riser provides the constant top tension to accommodate the stress and deformation of the riser,so it is the key factor to ensure the stability of subsea wellhead system.The mechanical analysis model and the deflection differential equation for subsea wellhead system were established after T he influences of ocean current,platform offset ,seabed soil and top tension were studied comprehensively.Then,the bending moment and transversal displacement characteristics of riser system under different top tension ratios (tension ratio: 0.9,1.0,1.1,1.2,1.5) were analyzed based on the theoretical model.Finally,the influence of top tension on the stability of subsea wellhead was analyzed by using the method of mechanical equivalent transformation.It is indicated that when subsea wellhead is installed in place,the top tension of axial load is the only controllable factor influencing the stability of subsea wellhead if the platform offset is constant.The stress and deformation of riser and subsea wellhead can be improved further by increasing the top tension of the riser.Based on the calculation method of minimum top tension,it is beneficial for the stability of subsea wellhead system in the field of deepwater drilling to set the tension ratio at 1.0-1.5.