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基于实际井眼轨迹的钻柱动力学特性有限元分析

Finite Element Analysis of Dynamic Characteristics of Drillstring Based on Actual Well Path

【作者】 胡以宝

【导师】 狄勤丰;

【作者基本信息】 上海大学 , 工程力学, 2011, 博士

【摘要】 石油钻井过程中钻柱的振动不可避免。剧烈的钻柱振动不仅会降低钻井效率,还会引发钻柱失效事故,增加钻井成本。国内外对钻柱失效的研究已经很多,但主要集中在改善钻柱的结构和材质方面。直到上世纪末,国外Baker Hughes、Schlumberger公司才在钻柱动力学特性研究方面取得突破性进展,并在钻柱振动和失效控制方面得到应用,获得了明显的经济效益。国内在这方面的研究起步较晚,理论研究相对落后,工程应用方面差距更大。因此,开展具有实用价值的钻柱非线性动力学特性研究对保障我国深井、超深井钻柱的安全性十分重要。有限元法广泛应用于钻柱动力学分析已达数十年,但仍旧局限于直梁单元和平面圆弧曲梁单元。对于三维弯曲井眼中钻柱的动力学特性分析,采用直梁单元和平面圆弧曲梁单元,其计算精度低、耗时长,全井钻柱,尤其是深井、超深井全井钻柱动力学特性计算更加困难,而运用空间曲梁单元来进行钻柱动力学特性的研究目前未见报道。而且,目前的研究中大都只给出了钻柱的变形、涡动轨迹、涡动速度等信息,而“钻柱的动态安全性评价”这一石油钻井工程师十分关心的问题则很少涉及。本文以了解和掌握井下钻柱的运动状态、减少钻柱失效事故、提高钻柱的安全可靠性为目标,应用空间曲梁有限元方法开展了基于实际井眼轨迹的钻柱动力学特性研究,开发了专用仿真计算程序,提出了钻柱的动态安全性评价方法。主要工作如下:1)建立了以空间曲梁单元为基础的钻柱动力学有限元分析模型,并利用该模型仿真计算了实际井眼轨迹条件下钻柱的动力学特性。2)提出了一种改进的有限元节点迭代方法,其不但能够求解直梁单元的钻柱动力学模型又能够求解空间曲梁单元的钻柱动力学模型。同时,验证了直梁单元、空间曲梁单元模型的可靠性,考察了直梁单元、空间曲梁单元的适用范围及其有效性。在此基础上开发了钻柱动力学特性仿真程序DDCS(Drillstring Dynamic Characteristics Simulation System),并利用理论算例和工程实测结果,验证了基于空间曲梁单元的钻柱动力学模型和DDCS的正确性。3)运用DDCS分析了全井钻柱的动力学特性,包括钻柱的涡动轨迹和涡动速度、钻柱的横向振动和轴向振动水平等;成功模拟了典型的钻柱运动现象——粘滑运动,分析了添加减振器前后钻柱轴向振动水平、轴向位移、轴向作用力的变化情况,从工程实例角度验证了基于空间曲梁单元的钻柱动力学模型和DDCS的正确性。4)分析了带铝合金钻杆钻柱的动力学特性,合理解释了铝合金钻杆容易产生划痕、压痕的原因,比较了钢质钻杆、铝合金钻杆动力学特性的异同,得出“含铝合金钻杆的钻柱更适宜采用井下动力驱动方式工作”的重要结论。5)实现了长度超过7000m的超深井钻柱的动力学特性的仿真计算,给出了钻柱的涡动轨迹、涡动速度和加速度等特性,研究了钻压、转速对钻柱动力学特性的影响规律。6)从钻柱动力学特性和第四强度理论出发,提出了钻柱的动态安全性评价方法——动态安全系数法。考虑钻柱与井壁的接触、碰撞作用等动态因素与静载水平,给出了钻柱的动态安全性评价标准,并以塔里木油田DB3井为例,分析了钻柱的动态安全状况并推荐了合理的转速、钻压范围。

【Abstract】 During drilling operations, drillstring vibrations occur frequently and can’t be avoided completely, which not only reduce the rate of penetration and the longevity of down-hole tool, but also result in drillstring failure. Many research works have been carried out on preventing drillstring failure, but were mainly focused on the structure and material of drillstring. Up to the end of the 20th century, break-through in the field of dynamics had been achieved by some overseas companies, such as Baker Hughes, Schlumberger, et al., to prevent the drillstring vibrations and failure, and a great deal of profit have been obtained. However, limited relevant studies and practical vibration control methods associated with drillstring dynamics are reported in China, so the study of drillstring dynamic characteristics has practical value to ensure the safety of drillstring in deep and ultra-deep oilwell.Although the finite element method has been widely utilized in dynamic analysis of drillstring for decades, it was limited in straight beam element and two-dimensional arc curved beam element. When they are used to analyze dynamic characteristics of drillstring in 3D-curved wellbore, a long time will be taken, and, thus, both?accuracy and efficiency of calculation are decreased. All of these make the dynamic characteristics analysis of drillstring in whole borehole difficult, especially for the drillstring of deep and ultra-deep well. An effective method which uses spatial curved beam element to analyze the drillstring dynamic characteristics in 3D-curved wellbore has not been reported yet. Furthermore, evaluation of drillstring dynamic safety has become a major concern of drilling engineers, but it is rarely studied by scholars. In order to understand the motion of downhole drillstring, minimize the drillstring failure and ensure the safety and reliability of drillstring, the spatial curved beam finite element method has been studied and a simulation program has been developed. At the same time, evaluation method of drillstring dynamic safety was studied in this thesis. The main contributions are summarized as follows:First, based on the spatial curved beam element, a new model of drillstring dynamics was proposed to analyze the dynamic characteristics of drillstring with double nonlinearity based on actual well path.Second, an optimized iterative method has been used to solve the nonlinear dynamics of drillstring effectively, which is compatible with straight beam element and spatial curved beam element. The adaptability and reliability of straight beam element and spatial curved beam element have been studied. Based on the new dynamic model and the optimized computation method, the simulation software DDCS (Drillstring Dynamic Characteristics Simulation System) has been developed, and the simulation results are consistent with the analytical as well as measurement data, which validated the model and the computation method.Third, the dynamic characteristics of drillstring in whole borehole, including whirl, lateral vibration and axial vibration, were analyzed by DDCS. Case studies on both stick-slip motion and dynamic characteristics analysis with and without vibration absorber were presented, and then the model and DDCS were then validated practically.Fourth, an analysis of dynamic characteristics of drillstring with aluminum alloy drill pipes was carried out. The differences between the dynamic characteristics of steel and aluminum alloy drill pipes were also obtained. The reasonable explanation was presented why aluminum alloy drill pipe is easy to scratch and indentation damage on its surface, and an important conclusion was summarized that aluminum alloy drill pipes prefer to be driven by power equipment at bottom hole.Fifth, the dynamic characteristics, the whirl orbit ,whirl speed and acceleration, et al., of drillstring over 7,000 meters long in the ultra-deep well was simulated successfully with DDCS, and, the effects of WOB (weight on bit) and rotary speed on the dynamic characteristics were obtained.Finally, in view of the contact and collision between drillstring and wellbore as well as the static stress of drillstring, a evaluation model of drillstring dynamic safety was firstly established based on drillstring dynamic characteristics and the fourth strength theory. Case study on dynamic safety of drillstring of DB3 well in Tarim Oilfield was made, and the reasonable rotary speed and WOB were presented.

  • 【网络出版投稿人】 上海大学
  • 【网络出版年期】2012年 07期
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