改善水泥浆与CO2污染钻井液的相容性技术措施

水泥浆与钻井液之间的接触污染对固井顶替效率和施工安全影响巨大，其原因之一是来自于地层的CO₂对钻井液的污染导致水泥浆与钻井液相容性恶化。为此，选择了四川盆地川东地区3口井的水泥浆与CO₂污染的钻井液进行相容性实验，结果表明，水泥浆与CO₂污染的钻井液混合后，浆体的流动性变差，稠化时间快速下降，仅靠简单的对钻井液降黏度切力、调整pH值技术措施已不能满足固井施工作业的要求。按改善水泥浆与CO₂污染钻井液相容性的技术路线，研究总结出了固井前处理受CO₂污染钻井液的4个技术对策，包括部分或全部置换井筒受污染钻井液、对污染的钻井液进行过饱和Ca²⁺处理、加入钻井液抗污染处理剂和合理设计前置液用量，满足了钻井液与水泥浆的相容性实验及生产要求，可有效地指导固井注水泥的安全施工。在目前国内外缺乏统一规范的相容性实验方法情况下，川东地区固井前所采用的处理CO₂污染钻井液的技术做法对于进一步完善天然气井固井准备的技术措施具有参考价值。

Technical measures for improving compatibility of cement slurry with CO2 contaminated drilling fluid: A case study

The contact pollution between cement slurry and drilling fluid greatly reduces the cement displacement efficiency and the construction safety. One of the causes is the deteriorated compatibility between cement slurry and drilling fluid contaminated by CO₂ in the formation. To solve this problem, a compatibility experiment was conducted on the cement slurry and CO₂ contaminated drilling fluid from 3 wells in the eastern Sichuan Basin, and the results showed that: with the cement slurry mixed with the CO₂ contaminated drilling fluid, the fluidity decreased and the thickening time was shortened rapidly. Therefore, simple technical measures were no longer sufficient for the well cementing construction, such as viscosity and shear reduction as well as pH regulation. Following the technical route of improving the compatibility between cement slurry and CO₂ contaminated drilling fluid, four technical countermeasures were presented for treating CO₂ contaminated drilling fluid before cementing, including: i) partially or completely replacing the polluted wellbore drilling fluid; ii) treating the contaminated drilling fluid with over saturated Ca²⁺; iii) injecting anti polluting agents into the drilling fluid; iv) using pad fluid in a proper quantity. Overall, these measures meet the requirements of the compatibility experiment (on drilling fluid and cement slurry) and the production, and can effectively improve the cementing safety. At present, no unified specifications are available for the compatibility experiment at home and abroad, so this case study has a certain reference value in further improving the technical measures of cementing preparation for natural gas wells.