地下储气库注采井不同井段水泥环密封性能实验

An experimental study on the sealing performance of cement sheath in different sections of injection/production wells of an underground gas storage

针对我国西南地区首座地下储气库--相国寺储气库投产后注采井出现较大比例的B环空异常带压问题,采用室内实验的方法,根据注采井100 m、900 m、2000 m垂深处温度和压力差异,设计了不同的水泥石养护温度和加载围压,并采用小尺寸的水泥环完整性测试装置基于应力等效原理测试了从井底到井口水泥环在试压和注采时的密封能力。实验结果表明:①井筒不同深度段水泥候凝温度和围压差异较大,同一种水泥浆体系在实际固井后沿井筒深度具有不同的机械性能,导致不同井段水泥环密封性能存在着巨大的差异;②交变载荷会导致水泥环的压实和累积损伤,加剧水泥环的密封失效;③注采井2000 m处水泥环在试压和注采工况条件下,密封性完好,没有发生泄漏,1000 m处水泥环在试压工况下能保持完好,在循环交变载荷下存在着水泥环密封失效的现象,井口附近100 m处水泥环在试压工况和注采工况时均出现了泄漏;④实验结果揭示,在试压和注采工况下,井筒中上部水泥环密封失效是造成B环空异常带压的根本原因。结论认为,该研究成果可以为提高地下储气库注采井固井水泥环密封的可靠性提供实验数据支撑。

After the Xiangguosi underground gas storage,the first underground gas storage in southwestern China,was put into operation,B-annulus abnormal pressure occurred in a larger proportion in injection/production wells.To solve this problem,this paper carried outalaboratory tests to design different set cement curing temperatures and confining pressures according to the variation of temperature and pressure at the vertical depths of an injection/production well,e.g.100 m,900 m and 2000 m.Then,based on the stress equivalence,a small-size cement sheath integrity testing device was used to test the sealing capacity of cement sheath from the bottom hole to the wellhead during pressure test and injection/production.And the following experimental results were obtained.First,cement setting temperature and confining pressure vary greatly in different depth sections of the wellbore,and the same cement slurry system presents different mechanical properties along the wellbore depth after actual cementing,which leads to great differences in the sealing performance of cement sheath in different hole sections.Second,alternating load can lead to compaction and cumulative damage of cement sheath,aggravating its sealing failure.Third,at the depth of 2000 m in an injection/production well,the cement sheath presents a good sealing performance without leakage under the working conditions of pressure test and injection/production.At the depth of 1000 m,it is intact under the working condition of pressure test,but its sealing gets failed under cyclic alternating load.And at the depth of 100 m near the wellhead,leakage occursunder the working conditions of pressure test and injection/production.Fourth,the experimental results show that the sealing failure of cement sheath in the middle and upper parts of the wellbore is the root cause of the B-annulus abnormal pressure under the working conditions of pressure test and injection/production.In conclusion,the research results can provide experimental data support for improving the sealing reliability of cement sheath in injection/production wells of an underground gas storage.