高温高压气井多封隔器管柱完整性分析方法及应用实例

Integrity analysis method of multi-packer string in HTHP gas wells and its application cases

为了分析计算多封隔器管柱的力学行为并评价封隔器的完整性,以压裂施工载荷工况下的双封隔器管柱系统的完整性为研究对象,提出了管柱力学全长分析与封隔器芯轴三维有限元分析结合的综合分析方法,并给出了相关的分析计算流程。以塔里木盆地迪西1井的弹塑性力学分析为例,首先对整体管柱全长进行了三维有限元分析,求取在管柱各处的应力分布;然后采用三维实体单元分析封隔器芯轴的局部结构中的应力分布与塑性应变分布,判别双封隔器管柱作业的安全性。研究结果表明:①在重力、液体压力和温度应力的作用下,管柱各处的轴向应力状态为拉应力,处于弹性应力范围;②在管柱轴向应力和液体压力共同作用下的芯轴发生了明显的塑性变形;③为了缓解压裂施工导致的温度下降引起的轴向拉应力过大的现象,应在两个封隔器之间加装伸缩节。结论认为,该方法用于分析多封隔器管柱得到的变形及应力分布数值结果与实际情况能很好的匹配,证明了该方法的有效性和实用性。

In order to analyze and calculate the mechanical behavior of multi-packer string and to evaluate the integrity of packer, this paper took the integrity of a double-packer string system under the loading conditions of fracturing construction as the research object to advance a comprehensive analysis method which combines the full-length string mechanics analysis with the 3 D finite element analysis of packer’s mandrel. In addition, the related analysis and calculation workflow was provided. A case study was carried out on the elastoplastic mechanics of Well Dixi 1 in the Tarim Basin. Firstly, 3 D finite element analysis was performed on the entire pipe string in the full length to figure out the stress distribution along the pipe string. Then, 3 D solid element was used to analyze stress distribution and elastoplastic strain distribution in the local structure of packer’s mandrel to determine the operation safety of double-packer pipe string. And the following research results were obtained. First, under the action of gravity, hydraulic pressure and temperature stress, the axial stress on each part of the string is tensile stress, which is in the scope of elastic stress. Second, under the joint action of axial stress and hydraulic pressure, the mandrel suffers obvious plastic deformation. Third, in order to alleviate the excessive axial tensile stress induced by the temperature drop caused by fracturing construction, an expansion joint shall be installed between two packers. In conclusion, the numerical results of the deformation and stress distribution of multi-packer string calculated by this method are well accordant with the actual situations, which verifies the effectiveness and practicability of this method.