环空体积膨胀条件下的高压气井环空压力预测方法

Prediction of sustained casing pressure in high-pressure gas wells under annular volume expansion

针对高压气井生产过程中气窜引发的环空带压问题,重点考虑自由段和封固段套管柱变形引起的环空体积变化,建立了2层环空压力耦合分析模型与数值求解方法,并对该模型进行了验证与算例分析;在此基础上,讨论了综合渗透率、环空气柱温度及环空液体密度等因素对环空压力的影响规律。结果表明:由于气窜的影响,自由段和封固段的套管柱膨胀,使A环空(油管与油层套管之间的环空)体积减小,而使B环空(油层套管与技术套管之间的环空)体积增大;环空体积变化延长了稳定时间,但A,B环空的最大压力均保持不变;随着综合渗透率和环空气柱温度的增加,最大环空压力不变,稳定时间缩短;随着环空液体密度的增加,最大环空压力减小,稳定时间缩短。因此,防止水泥环损坏、降低环空气柱温度及提高环空液体密度,是缓解高压气井环空带压的有效措施。该研究对高压气井井筒完整性的评估与控制具有指导意义。

For the sustained casing pressure(SCP)triggered by gas migration in production process of high pressure gas wells,the annulus volume change caused by the deformation of the casing string at the free and cemented section is focused in this paper.The coupling analysis model and numerical solving method of SCP of two-layer casing string at wellhead are established and proved by instance analysis.The influential factors to SCP such as composite permeability of cement sheath,temperature of gas column and annulus fluid density are discussed.The results show that,influenced by gas channeling,casing string at the free and cemented section deforms,and volume(annulus A)between tubing and production casing is reduced,while the volume(annulus B)between production casing and intermediate casing is increased.The time required by the pressure of annulus A and B to be stable is extended,but both the maximum pressures remain unchanged.The higher the composite permeability of cement sheath and the temperature of annulus gas,the shorter the time for annular pressure to be stable.The maximum annular pressure decreases with the increase of fluid density,and the time required for the annular pressure to be stable extends.Therefore,to prevent cement sheath from damage,reduce temperature of annular gas column and increase liquid density of annulus are effective to relieve SCP of high-pressure gas well.The study is significant for the integrity evaluation and control of wellbore with high-pressure gas wells.