控制水泥浆失水性能的新认识

NEW CONGIZANCE OF CONTROLLING WATER LOSS PERFORMANCE OF CEMENT SLURRY,NGI

水泥浆滤失受到井壁内外泥饼及不同渗透率岩心的阻挡作用，其失水量比ＡＰＩ标准所测数值小很多，当水泥浆ＡＰＩ失水量为２５０ｍＬ／３０ｍｉｎ×７ＭＰａ时，模拟井下的实际失水量约为７～１２ｍＬ／３０ｍｉｎ×７ＭＰａ。因此，在注水泥时，较大的水泥浆失水不会造成系压的急剧增高；也不会在水泥浆凝结过程中形成桥堵，引起油、气、水窜及损害油、气层等问题。水泥浆失水的主要作用，在于保持一个良好、稳定、自由水少的水泥浆体系，使水泥石均匀地分布在环形空间内，既提高了水泥环质量，对防止气窜也有好处。

Cement slurry filtration is affected by the resistances of the mud cakes inside and outside borehole wall and the cores with various Permeability. The water loss is very smaller than the value measured by API standard. If API water loss of cement slurry is 250 mL/30 min×7 MPa,the actual water loss of simulation downhole is about 7～12 mL/30 min×7 MPa.So, while cementing, larger cement slurry water loss does not make pumping pressure raise sharply and does not form brigeblocking in the course of cement slurry condensation to cause oil-gas-water breakthrough and oil-gas bed damages. The main action of cement slurry water loss is keeping a good and stable slurry system with small free water to make cement distribute well in annular space, which not only can enhance the quality of cement hoop, but is favourable for avoiding gas breakthough.