水下井口生产热膨胀力分析与井口环空密封完整性评估

Analysis of Thermal Expansion Force and Integrity Evaluation of Wellhead Annulus Sealing During Production of Underwater Wellhead

基于南海东部某海域的钻井资料,运用热力、结构力学理论,建立水下井口的热-结构力学轴对称有限元模型,运用ANSYS软件对海床以上井口的轴向热膨胀力进行计算。采用经典理论计算套管串由于热膨胀在井口产生的力,对环空密封总成的长期密封完整性进行评估。结果表明,在4285 m井深和正常温度压力条件下,由于流体热循环在套管挂处产生向上的力为2811 kN,而环空密封总成锁环工作能力为3247 kN,因此,环空密封总成锁环可抵抗热膨胀产生的向上的力。为确保油井生命周期的井口安全,提出在套管挂顶部下入锁紧补芯,以限制套管挂和密封总成在生产过程中由于热膨胀而向上移动。上述评估方法及措施为水下井口在生产过程中的密封完整性评估提供参考。

An axisymmetric finite element model of thermal-structural mechanics is established based on the actual drilling data in the east of the South China Sea and the theory of thermodynamics and structural mechanics to calculate the axial thermal expansion force at the wellhead above seabed by ANSYS software.The axial force caused by thermal expansion of the casing string is calculated by classical theory,so as to evaluate the sealing integrity of the Annulus Sealing Assembly(ASA)in the long term.It is indicated that the axial upward force caused by fluid heat circulation at the casing hang is 2811 kN under the condition of 4285 m well depth and normal temperature and pressure,but the working capacity of the ASA lock ring is 3247 kN,so the ASA lock ring can resist the upward force due to thermal expansion.In order to guarantee the sealing integrity of the ASA throughout the design life of the well,it is recommended to use a lockdown device at the top of the casing hanger to prevent the vertical movement of the casing hanger and ASA.The methods and measures are of useful reference for the integrity evaluation of the wellhead annulus seal during production.