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首页> 外文会议>International Association of Drilling Contractors and Society of Petroleum Engineers Drilling Conference and Exhibition >Dynamic Model for Stiff String Torque and Drag
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Dynamic Model for Stiff String Torque and Drag

机译：刚性弦扭矩和拖曳动态模型

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A dynamic stiff string torque and drag (T&D) model is presented that assumes steady state motion of the drillstring as its basis for calculations. Results are compared to previously published T&D models that are based on static equilibrium. The novelty of the new dynamic model is the ability to solve T&D operations of the entire drillstring from bit to top drive in reasonable time using standard engineering computers. The new approach is based on a 3D dynamic model of drillstring and BHA in an elastic borehole. It considers bending stiffness, torsional stiffness, contact forces, and friction with localization of contact points. A numerical method is described that has proven to have excellent convergence. Complete governing equations are provided and the method is described in detail to permit readers to replicate results. The dynamic model is compared to two static stiff string models. Comparisons are also provided for three conventional soft string models including the Lubinski-Paslay-Cernocky bending stress magnification factor. Three field case studies are presented for horizontal wells. One well is short radius with dogleg severity over 50 deg/100 ft and two wells are unconventional shale wells with doglegs up to 15 deg/100 ft. Predictions for surface torque and drag up and down for the new dynamic stiff string model are compared to the static stiff and soft string models. In many situations modeled the top-level results for surface torque and drag up/down are close enough for all six models to be within the uncertainty range associated with the commonly used, lumped-parameter friction factor. However, some major differences in hook load for sliding and slack off operations are observed, which are shown to be caused by differences in location and magnitude of contact force between the drillstring and wellbore. Further, significantly lower surface torque is predicted by the new dynamic stiff string compared to other models for one case history because of lower contact forces in the vertical section of the well. In fact, the key finding of this paper is that major differences are observed for contact forces for the new dynamic stiff string model compared to all five other models, including the two static stiff string models. These differences in contact forces are most significant when the drillstring has helically buckled or when doglegs in the wellbore are high. Contact forces have a large impact on local stress behavior, which is important for predictions of casing and drillpipe wear, drillstring fatigue, and failure points in the drillstring. Although several previous papers have published stiff string models there is no industry standard formulation. The main problem holding back the development of an industry standard stiff model is perhaps the complexity of the numerical algorithm and substantial running time. To address this problem, some previous stiff string models account for bending stiffness of the drillstring but not for radial clearance while others appear to model only portions of the drillstring as stiff. The new stiff string model accounts for bending stiffness and radial clearance for the entire drillstring while still giving reasonable computational times. For stiff string models the advantage of using a dynamic approach to solve the steady state position of the drillstring is mainly related to superior convergence of the numerical algorithm compared to static stiff string models because calculation of contact points is faster.
机译：提出了一种动态刚性串扭矩和拖动（T＆D）模型，其假设钻机的稳态运动作为其计算的基础。将结果与先前公布的T＆D模型进行了比较。新动态模型的新颖性是能够在合理的时间使用标准工程计算机在合理的时间内从位到顶部驱动器来解决整个钻头的T＆D操作。新方法基于钻孔钻孔中的钻孔和BHA的3D动态模型。它考虑了弯曲刚度，扭转刚度，接触力和摩擦与接触点的定位。描述了一种证明具有优异的收敛性的数值方法。提供了完整的管理方程，并详细描述了该方法以允许读者复制结果。将动态模型与两个静态刚性串模型进行比较。还提供了三种传统的软弦模型，包括Lubinski-Paslay-Cernocky弯曲应力放大系数的比较。提供了三个现场案例研究，用于水平孔。一个良好的是短半径，牧草严重程度超过50°/ 100英尺，两个井是非传统的页岩井，带有狗腿，高达15°/ 100英尺。对表面扭矩的预测和向上和向下拖动的新动态僵硬串模型静态僵硬和软弦模型。在许多情况下，建模的表面扭矩的顶级结果，并拖动/下降足够接近所有六种模型，以便在与常用的大次参数摩擦系数相关联的不确定性范围内。然而，观察到用于滑动和松弛操作的钩载荷的一些主要差异，其被示出由钻头和井筒之间的接触力的位置和大小的差异引起。此外，由于井中的垂直部分中的垂直部分中的接触力较低，通过新的动态刚性串预测了新的动态刚性串的显着降低的表面扭矩。事实上，本文的关键发现是，与所有五种其他型号相比，新动态僵硬串模型的接触力被观察到主要差异，包括两个静态僵硬弦模型。当钻杆螺旋弯曲或井筒中的脱皮很高时，接触力的这些差异最为显着。接触力对局部应力行为产生了很大的影响，这对于钻石和钻孔管磨损，钻孔疲劳和钻孔钻头的故障点是重要的。虽然上述几篇论文发布了僵硬的字符串模型，但没有行业标准配方。阻止行业标准僵硬模型的发展的主要问题可能是数值算法的复杂性和大量运行时间。为了解决这个问题，一些先前的刚性弦型模型用于钻头弯曲的弯曲刚度，但不是用于径向间隙，而其他则似乎仅为钻孔的部分造型为僵硬。新的僵硬的弦模型用于整个钻孔的弯曲刚度和径向间隙，同时仍提供合理的计算时间。对于僵硬的弦模型，使用动态方法来解决钻机的稳态位置的优点主要与静态僵硬串模型相比，数值算法的优异收敛性，因为接触点的计算更快。

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