刚果钾盐钻探用钙镁基钻井液研究及应用

在钾盐钻探过程中，采用常规水基钻井液普遍存在孔壁溶蚀扩径、岩心采取率低等问题。而采用油基钻井液虽然可以保证取心质量，但是成本高且环保性能差。因此，研究一种能高质量获取钾盐矿心且成本低的水基钻井液是极为必要的。基于前期钾盐钻探水基钻井液研究成果，针对刚果共和国光卤石型钾盐地层特点及绳索取心钻探要求，本文采用浸泡模拟实验和材料配伍性对比实验研究，攻关了抑制氯化钙、氯化镁和氯化钾溶解技术，研发了一套钙镁基钻井液配方，具体为：30%氯化镁+20%~30%氯化钙+1%锁水抑制剂+2%~3%钠膨润土+1.3%~1.6%接枝淀粉GSTP +0.4%~0.7%增黏剂GTQ+0.4%包被剂GBBJ。该钻井液具有良好的流变性、悬浮携带能力以及抑制光卤石和溢晶石溶解的能力。并且在刚果共和国奎卢省钾盐钻探工程成功应用，解决了以往使用常规水基钻井液出现的地层溶蚀和岩心采取质量差等问题，顺利完成钻探工作量3020余米，盐矿心采取率达98%以上，节约钻井液成本80%以上。钙镁基钻井液在光卤石型钾盐绳索取心钻探工程中的首次应用表明其可以完全替代油基钻井液，在钾盐钻探工程中具有广阔的推广应用前景。

Research and application of calcium-magnesium-based drilling fluid for potassium salt in Republic of Congo

In the process of potassium salt drilling, conventional water-based drilling fluids often encounter hole wall dissolution and expansion and low core recovery. Oil-based drilling fluids can ensure core quality, but have high cost and poor environmental performance. It is therefore extremely necessary to develop a kind of low-cost water-based drilling fluid suitable for high-quality potassium salt coring. Based on the previous research of water-based drilling fluids for potassium salt drilling, and aiming at the characteristics of carnallite-type potassium salt formation and the requirements of wireline coring drilling in Republic of the Congo, this work developed a set of calcium-magnesium-based drilling fluid formula to solve the problem of inhibition technology of calcium chloride, magnesium chloride and potassium chloride dissolution, i.e., 30% magnesium chloride +20%~30% calcium chloride +1% water-locking inhibitor +2%~3% sodium bentonite +1.3~1.6% graft starch GSTP +0.4%~0.7% viscosifier GTQ+0.4% flocculating agent GBBJ. This drilling fluid has good rheology, suspending and carrying capacity and ability to inhibit dissolution of carnallite and tachyhydrite. Moreover, it was successfully applied in potassium salt drilling project in Kweilu Province, Republic of the Congo. And problems of potassium salt formation dissolution and poor core quality with using conventional water-based drilling fluids was solved. The drilling workload of more than 3020 m was successfully completed with core recovery over 98%, and the cost of drilling fluid was saved more than 80%. The first application of calcium-magnesium-base drilling fluid in the wireline coring drilling project of carnallite-type potassium salts shows that it can completely replace oil-based drilling fluid, and has a broad application prospect in potassium salt drilling project.