完井作业油管柱失效的力学机理——以塔里木盆地某高温高压井为例
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摘要
塔里木盆地某高温高压井井深约7 000 m、地层温度180℃、地层压力120 MPa,该井在完井作业中发生两处油管工厂端丝扣根部断裂的工程问题。如何从管柱变形与应力变化进行解释并提出应对措施,进而保证管柱完整性和保障安全生产是一个值得讨论的问题。为此,采用有限单元法进行管柱的三维力学数值分析,建立起三维有限元管柱力学模型,模拟完井作业中下封隔器坐封、压裂、测试3个工况下的管柱结构变形,分析管柱系统的位移和应力的变化规律,进而基于疲劳强度计算的理论公式得出了疲劳安全系数的计算公式。研究结果表明:(1)依据该井完井管柱各处的轴向应力有限元数值计算结果,得到了各弯曲应力部位的疲劳安全系数值;(2)测试作业各油管段的疲劳安全系数都大于3,属于安全状态;(3)断裂的2段油管疲劳安全系数值分别为1.99和1.11,处于预警区,而其他管段的疲劳安全系数均大于1.99,属于安全区。结论认为,该方法为具有类似结构的超深高温高压井的管柱力学设计提供了有效的分析手段。
There is one HTHP well(high temperature, high pressure) in the Tarim Basin about 7 000 m deep with formation temperature 180 ℃ and formation pressure of 120 MPa. In the process of its completion operation, the root of thread at the factory end was broken at two points. Therefore, it is necessary to discuss the reasons for the breaking from the aspects of string deformation and stress change and propose the corresponding measures so as to ensure string integrity and production safety. In this paper, 3 D mechanics of strings was analyzed using finite element method. Then, a 3 D finite element string mechanics model was established to simulate the string deformation in 3 working conditions(i.e., packer setting, fracturing and testing) in the process of well completion and analyze the displacement of string system and the change laws of stress. Finally, the calculation formula of fatigue safety factor was derived based on the theoretical calculation formula of fatigue strength. And the following research results were obtained. First, the fatigue safety factor of bending stress positions is obtained based on the finite-element numerical calculation results of axial stress at different positions of completion string in this well. Second, the fatigue safety factor of each tubing section during the testing is higher than 3, so it is in the state of safety. Third, the fatigue safety factor of two broken tubing sections is 1.99 and 1.11, respectively, so they are marked as red-warning zones. The fatigue safety factor of other sections is higher than 1.99, so they are classified as safety zones. In conclusion, this method provides an effective analysis means for the string mechanics design of similar ultra-deep HTHP wells.
There is one HTHP well(high temperature, high pressure) in the Tarim Basin about 7 000 m deep with formation temperature 180 ℃ and formation pressure of 120 MPa. In the process of its completion operation, the root of thread at the factory end was broken at two points. Therefore, it is necessary to discuss the reasons for the breaking from the aspects of string deformation and stress change and propose the corresponding measures so as to ensure string integrity and production safety. In this paper, 3 D mechanics of strings was analyzed using finite element method. Then, a 3 D finite element string mechanics model was established to simulate the string deformation in 3 working conditions(i.e., packer setting, fracturing and testing) in the process of well completion and analyze the displacement of string system and the change laws of stress. Finally, the calculation formula of fatigue safety factor was derived based on the theoretical calculation formula of fatigue strength. And the following research results were obtained. First, the fatigue safety factor of bending stress positions is obtained based on the finite-element numerical calculation results of axial stress at different positions of completion string in this well. Second, the fatigue safety factor of each tubing section during the testing is higher than 3, so it is in the state of safety. Third, the fatigue safety factor of two broken tubing sections is 1.99 and 1.11, respectively, so they are marked as red-warning zones. The fatigue safety factor of other sections is higher than 1.99, so they are classified as safety zones. In conclusion, this method provides an effective analysis means for the string mechanics design of similar ultra-deep HTHP wells.
引文
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[3]丁亮亮,杨向同,刘洪涛,张宇.超深水平井尾管悬挂器下部环空压力预测及其应用[J].石油钻采工艺,2015,37(5):10-13.Ding Liangliang,Yang Xiangtong,Liu Hongtao&Zhang Yu.Prediction and application of lower annular pressure of hanger of ultra-deep horizontal well[J].Oil Drilling&Production Technology,2015,37(5):10-13.
[4]沈新普.超深井套管三维弹塑性ABAQUS有限元分析[J].天然气工业,2007,27(2):54-56.Shen Xinpu.ABAQUS FEM analysis for elastoplasticity of casing used in ultradeep wells[J].Natural Gas Industry,2007,27(2):54-56.
[5]沈新普,沈国阳.复杂结构井钻压值的有限元数值计算[J].计算机辅助工程,2013,22(增刊2):312-316.Shen Xinpu&Shen Guoyang.Finite element numerical calculation on axial force along drilling tube for complex wells with finite element method[J].Computer Aided Engineering,2013,22(S2):312-316.
[6]沈新普,沈国阳.致密砂岩油层改造压力作用下双筒液压封隔器弹塑性承载能力三维数值分析[J].计算机辅助工程,2013,22(增刊2):307-311.Shen Xinpu&Shen Guoyang.3D numerical analysis on bearing capacity of dual piston hydraulic packer under reservoir stimulation pressure for tight sand[J].Computer Aided Engineering,2013,22(S2):307-311.
[7]曾春华,邹十践.疲劳分析方法及应用[M].北京:国防工业出版社,1991.Zeng Chunhua&Zou Shijian.Methods and applications of fatigure analysis[M].Beijing:National Defense Industry Press,1991.
[8]王学颜,宋广惠.结构疲劳强度设计与失效分析[M].北京:兵器工业出版社,1992.Wang Xueyan&Song Guanghui.Structural fatigue strength design and failure analysis[M].Beijing:Weapon Industry Press,1992.