摘要
水泥环的密封完整性对降低环空带压、提高井筒安全性、延长气井开采寿命至关重要。为防止环空气窜,高温高压气井油层套管水泥一般返至井口,这给深井固井带来了巨大挑战。考虑井身结构和作业载荷的复杂性,运用Ansys软件建立了存在自由套管时水泥环受力有限元模型,研究了自由套管长度和井口套压对水泥环应力的影响,结果表明,井口套压作用下自由套管的鼓胀效应在水泥环中产生的径向拉应力和轴向应力是水泥环密封失效的主要原因。自由套管段长度对水泥环受力很不敏感,油层套管水泥可考虑不返至井口,但为保持水泥环长期完整性应避免过高井口套压,同时优选水泥浆体系以提高套管与水泥环胶结强度。
Seal integrity of cement sheath is critical to reduce annular sustained casing pressure,improve wellbore safety and prolong the service life of gas well.For preventing annular gas channeling,the annulus of production casing in HTHP gas wells is always cemented to the ground,which brings a huge challenge to cementing of deep wells.If the cement does not return to the wellhead,the free casing under the action of wellhead casing pressure will affect the local stress and failure of cement mantle.Because of the complexity of the wellbore structure and downhole load,existing analytical models are difficult to accurately simulate the stress of cement sheath under complex load condition.So,through the Ansys software,the finite element model(FEM) of cement sheath stress considering free casing has been established to investigate the influence of the length of free casing and wellhead casing pressure on cement sheath stress,the results showed that:(1) when the wellhead casing pressure exists,the ballooning effect of free casing will produce radial tensile stress and axial stress in the cement sheath,if they are greater than the cementing strength of casing and cement sheath,it will make radial separation or axial sliding of the interface between casing and cement sheath,thus breaking the seal integrity of cement sheath.(2) when the wellhead casing pressure is constant,the stresses of cement sheath with different length of free casing almost remain unchanged,it indicates that the cement sheath stress is not very sensitive to the length of free casing.(3) when the length of free casing is constant,the stress in cement sheath increases as the wellhead casing pressure increases,considering the great decrease of seal integrity of cement sheath under a long time HTHP action,suggesting avoiding too high wellhead casing pressure,at the same time optimizing slurry system to improve the cementing strength of casing and cement sheath.The results provide references for the optimization of cement top in gas wells.
出处
《钻采工艺》
CAS
北大核心
2014年第2期75-78,119,共4页
Drilling & Production Technology
基金
国家自然科学基金项目(编号:50904050
51244007)
国家科技支撑计划(编号:2011BAE25B04)
四川省科技厅项目(编号:2011JY0106
13QNJJ0048)
中央财政支持地方高校发展专项资金"石油与天然气工程国家一级学科"项目的共同资助
关键词
气井
高温高压
水泥环
自由套管
有限元模型
应力
完整性
gas well
high temperature and high pressure
cement mantle
free casing
finite element model
stress
integrity
