油井水泥膨胀剂研究(Ⅰ)——水泥浆体的收缩与危害

Study on expandant of oil well cement (Ⅰ) : Volume shrinkage and damage.

水泥浆体的体积收缩使水泥环的胶结质量不能保证 ,严重时还可能形成微间隙 ,引发地层流体窜流 ;高滤失使得水泥浆在施工过程中发生脱水桥堵和失水收缩 ,水泥浆滤液进入油气层孔隙后 ,与地层内流体不配伍造成油气层污染。综合分析了油井水泥浆体在不同条件下的收缩特性、评价方法及其影响因素 ,讨论了固井作业中发生地下流体窜槽的原因和危害。分析结果表明 :油井水泥浆体固有的体积收缩是造成窜槽事故的根本原因。要从根本上解决固井后的窜槽问题和提高井下水泥环二界面胶结质量 。

Oil well cement has two fatal limitations when used in HTHP condition: high volume shrinkage and high filtration. The volume shrinkage of cement slurry body often cause poor bond quality, and even micro-clearance when the shrinkage is serious, and then formation fluids migration occur. Dehydration bridging Off and water-loss shrinkage often produced by the high filtration of cement slurry, and once the filtrate invade in the openings of oil/gas formation, damage will happen for its incompatibility with the for-mation fluids. The volume shrinkage of slurries, the testing methods and some factors influencing expan-sion were described according to various literatures. The reasons and damage of formation fluids migration during cementing were also discussed. Results showed that the intrinsic shrinkage of oil well cement slurry is the root of fluids migration, and to avoid the fluids migration problem after cementing and to improve bonding quality of two interfaces down hole, the problem of volume shrinkage of cement slurry body should be conquered firstly.