对比分析表3可知:①现场常用冲洗液清洗后的岩心界面胶结物中含有Mg、Al、Fe元素,这些元素来源于钻井液中处理剂,说明现场常用冲洗液无法有效地将岩心上滤饼的清洗干净。②现场常用冲洗液清洗后的岩心胶结物中O元素含量明显高于新型固井冲洗液WD-C清洗后的岩心胶结物,除了水泥中硅酸盐物质的O元素外,还含有大量钻井液中碳酸钙、重晶石加重剂和高分子聚合物等物质,碳酸钙(caCO3)、重晶石(BaS0。)和聚合物中所含有羟基、羧基和醛基等有机基团是使胶结物O元素含量高的主要原因。③新型固井冲洗液WD-C清洗后的岩心胶结物中含有较多Ca、Si元素,Ca、Si元素来源于水泥水化产物,说明新型冲洗液WD-C能够有效地清洗掉岩心上的滤饼,从而使水泥充填在岩心 滤饼水泥之间,并发生水化反应,有助于提高界面胶结强度。
5.3 界面胶结物的微观结构SEM分析
图4为现场常用冲洗液、WD-C冲洗后岩心与水泥浆存75℃养护24h的界面胶结物微观结构SEM对比。从图4中可明显看到在岩心与水泥石界面处水泥由于受到钻井液中膨胀土和聚合物外加剂的影响,水泥颗粒基本没有水化,水泥颗粒表面覆盖许多钻井液中的物质,而没有水泥的水化产物氢氧化钙(六方片状)和水化硅酸钙凝胶CSH物质(呈现纤维状)。而经过WD-C清洗后岩心与水泥石界面处的水泥颗粒能够正常水化,有明显的水化硅酸钙CSH凝胶和Ca(OH)2晶体,并且有大量呈棒状的钙矾石(AFt)生成,相互交织形成网络结构,从而有利于提高界面胶结强度。
6 结论
1)水基钻井液中的高分子聚合物物质会阻碍水泥颗粒的正常水化反应,从而大幅度降低固井二界面胶结强度,因此,高效地清除钻井液滤饼是提高固井二界面胶结质量的关键。目前常用固井冲洗液无法有效地清除掉水基钻井液滤饼,制约着固井质量的提高。
2)根据水溶性纤维在水溶液形成三维网络结构的强冲刷原理和滤饼氧化分解原理,设计并研究出一种新型的固井冲洗液WD-C。
3)冲洗液WD-C对水基钻井液滤饼具有优良的冲洗作用,能够在10min内将钻井液滤饼清洗干净,有效防止因残留滤饼层而引起的固井微间隙现象发生。
4)冲洗液WD-C对岩心表面水基钻井液及滤饼的高效清除,保证了固井水泥在水泥 岩心界面处的正常水化,生成水化硅酸钙凝胶、Ca(OH)2和棒状钙矾石(AFt)晶体,相互交织并形成致密网络结构,实现了固井二界面的有效胶结,有助于提高固井质量。
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