固井水泥浆与钻井液接触污染作用机理

针对固井时水泥浆和钻井液掺混易产生接触污染,造成注水泥憋泵和危及作业安全的问题,对接触污染的作用机理进行了研究。比较了掺混钻井液和钻井液处理剂前、后的水泥浆性能,利用红外光谱、X-射线衍射仪、扫描电镜对掺混前、后水泥浆的物相和微观形貌进行对比,确定钻井液和钻井液处理剂对水泥浆性能及结构的影响;利用原子吸收分光光度计测定水泥浆滤液中离子种类及含量,考察了各类金属离子对钻井液和处理剂溶液的影响。研究结果表明了接触污染作用机理:水泥浆中Ca²⁺对钻井液产生"钙侵 "造成钻井液流变性能变差;水泥水化产生的Fe³⁺、Al³⁺可与钻井液中的多种聚合物类处理剂交联形成凝胶,凝胶的形成加之处理剂对水泥颗粒的吸附架桥,造成水泥浆体多级絮凝结构的加强,导致混浆流动性急剧降低。根据作用机理,可使用抗钙先导浆、在隔离液中加入掩蔽剂等措施来解决接触污染。解决接触污染措施在ST1井、MX17井尾管固井中的应用效果良好,为保证深井注水泥安全提供了有力的技术支持。

Mechanism of cement contamination by drilling fluid

Mixing between the cement slurry and drilling fluid during cementing commonly leads to contact contamination, further causing pump blocking and thereby affecting the operation safety. Laboratory research was conducted to analyze the mechanism underlying contact contamination of cement slurry by drilling fluid. The properties of cement slurry before and after mixed with drilling fluid and drilling fluid additives are compared; additionally, the hydration phase composition and microstructure of cement slurry were analyzed using infrared spectroscopy, X-ray diffraction, and scanning electron microscopy, in order to determine the influence of drilling fluid and drilling fluid additives on cement properties and structure. Moreover, the species and contents of metal ions in cement slurry were analyzed using atomic absorption spectroscopy, in order to examine the influence of metal ions on drilling fluid and drilling fluid additives. The results showed that Ca²⁺ contained in cement slurry caused calcium invasion to drilling fluid, leading to a reduction in the fluidity. Al³⁺ and Fe³⁺ generated from hydration of cement slurry cross-linked with different polymer drilling fluid additives, leading to gel formation. The gelatification, together with adsorption bridging of addictive over cement particles, strengthened the multi-level flocculated structure of cement slurry, leading to a rapid decrease in the fluidity of mixed slurry. Based on the above mechanism, it is recommended to take measures such as using an anti-calcium pilot slurry and adding masking agents into the spacer fluid, in order to prevent cement contamination. The proposed measures were applied to liner cementing of wells ST1 and MX17, which achieved satisfactory results. This study provided a strong technical support to ensure the safety of deep well cementing.