高温高压井油套环空早期圈闭压力研究

Study on Trapped Pressure in Tubing-Casing Annulus at Early Production Stage in HTHP Wells

高温高压井生产初期,油套环空中由完井液热膨胀引起的环空圈闭压力会降低管柱、井口及封隔器的可靠性。为此,基于密闭空间能量传递理论、状态方程和弹塑性理论,建立了热膨胀影响下油套环空压力分布计算模型,分析了井底温度、井底压力、坐封深度及产量对油套环空圈闭压力的影响,并研究了气液共存状态下油套环空圈闭压力的变化规律。研究结果表明:井底温度能够大大提高环空圈闭压力,且油套环空距离油管最近,受到的影响最大;井底压力对油套环空圈闭压力影响较小,因为它不会直接改变环空的温压分布;气体的存在会大大降低油套环空圈闭压力,如果在气液共存状态下,油套环空仍存在较高的持续圈闭压力,则说明井筒完整性破坏,有窜流进入环空,现场作业时须采取注入气体的方式缓解环空圈闭压力。所得结果有助于提前预测井筒完整性状况并采取必要措施。

In the early stage of high-temperature and high-pressure(HTHP)well production,the trap pressure in the tubing-casing annulus caused by the thermal expansion of the completion fluid will reduce the reliability of the string,wellhead and packer.Therefore,based on the energy transfer theory in confined space,the equation of state and the elastoplastic theory,a calculation model for the pressure distribution of the tubing-casing annulus under the influence of thermal expansion is established.The influences of bottom hole temperature,bottom hole pressure,setting depth and production on the tubing-casing annulus are analyzed.The research results show that the bottom hole temperature can greatly increase the annulus trap pressure.The tubing-casing annulus is closest to the tubing,which is the most affected.The bottom hole pressure has little effect on the tubing-casing annulus trap pressure because it will not directly change the temperature and pressure distribution of the annulus.The presence of gas will greatly reduce the trap pressure of the tubing-casing annulus.If there is still a high continuous trap pressure in the tubing-casing annulus under the coexistence of gas and liquid,it indicates that the wellbore integrity is damaged,and there is channeling into the annulus.Gas injection is needed to relieve the annulus trap pressure during field operations.The results can help predict wellbore integrity in advance and take necessary measures.