SO_4^(2-)和HCO_3^-对油井水泥石的侵蚀研究

Erosive effects of SO_4^(2-) and HCO_3^- on oil well cement stone

利用X射线衍射仪、扫描电子显微镜、强度检测仪检测受腐蚀水泥石的产物、微观结构及抗压强度,分析调整井三次采油过程中HCO3和SO42共同作用下油井水泥石的腐蚀作用,研究腐蚀对强度产生的影响规律,为合理设计抗腐蚀水泥浆体系提供基础。结果表明:38~60℃条件下,SO42与HCO3协同侵蚀作用下,水泥石的主要腐蚀产物为石膏、钙矾石和方解石,水泥石物质组成及微观结构被改变,侵蚀后水泥石的强度比SO42或HCO3单独腐蚀时更低;腐蚀达到及超过21 d时,水泥石强度低于未腐蚀水泥石,随腐蚀时间的延长及混合液浓度的增高,强度大幅度下降;腐蚀14 d以内时,腐蚀后水泥石的强度随温度升高呈增加趋势,腐蚀达到及超过21 d时,随温度升高水泥石强度呈下降趋势。

The corrosion products,microstructure and compressive strength of corroded cement matrix were examined by using X-ray diffraction（XRD）,scanning electron microscopy（SEM） and strength test instrument.Corrosion of oil well cement stone by sulfate（SO42） and bicarbonate（HCO3） during enhanced oil recovery（EOR） in adjustment wells was analyzed.The erosive effects on the compressive strength were studied to provide theoretical foundation for reasonably designing corrosion resistance cement system.The results show that the main corrosive products of cement cooperatively eroded by SO42 and HCO3 were gypsum,ettringite and calcite under the temperature between 38 ~60 ℃,which has changed the material composition and microstructure of cement.Otherwise,the compressive strength of cement stone eroded by both of SO42 and HCO3 were much lower than that singly eroded by SO42 or HCO3 for all samples.When the corrosion time reached or exceeded 21 d,the compressive strength of corrosive cement was lower than that of un-corroded stone.The compressive strength of corrosive cement paste matrix precipitously declined with the increase of corrosion time and concentration of blend liquid of SO42 and HCO3.When the corrosion time was within 14 d,compressive strength of the corrosive cement paste matrix increased with the rise of corrosion temperature.And when the cement was eroded over than 21 d,compressive strength decreased with the increase of temperature.