巴彦河套盆地临河区块深层井壁失稳钻井液对策

巴彦河套盆地临河区块深层钻井过程中井壁失稳严重，制约油田的高效开发。利用X射线衍射、扫描电镜等分析测试方法对失稳地层岩样的黏土矿物成分和微观结构进行分析，确定井壁失稳原因主要是地层水敏性强，同时微裂缝发育，钻井液滤液侵入后，水楔作用下造成微裂缝扩张，地层水化引起坍塌压力的增加导致剥落掉块。解决井壁失稳的关键是针对性提高钻井液体系的抑制性和封堵性。结合现场钻井液技术需求,引入微纳米封堵剂提高钻井液体系的封堵能力、引入聚胺与KCl配合提高体系的抑制性能。室内实验表明，优化后的钻井液体系页岩膨胀降低率62%，滚动回收率可达90%以上。现场应用3口井，古近系地层平均井径扩大率小于20%，有效提高了巴彦河套盆地临河区块深层井壁稳定性,为油田的高效开发提供了技术支撑。

Drilling fluid solutions to well instability in deep layers of Linhe block of the Bayan Hetao Basin

Deep drilling in the Linhe block of the Bayan Hetao Basin suffers from severe well instability, which restrains the high-efficient development of the oilfield. The clay mineral composition and micro structure of the core samples of the troublesome layers were investigated via the X-ray diffraction analysis and scanning electron microscopy, respectively, which reveals that the well instability is mainly attributed to the high water sensitivity and well-developed micro fractures of the formations. Micro fractures are expanded by the water wedge of the invading mud filtrate and formation hydration raises the collapse pressure. These jointly lead to borehole wall caving. The key to solving well instability is to improve the inhibition and plugging performance of the drilling fluid system. Given this, the micro-nano plugging agents were introduced to improve the plugging performance of the drilling fluid system and the polyamine was added for synergy with KCl to enhance the inhibition performance. The laboratory experiments demonstrate that the optimized drilling fluid system presents a reduction of the shale swelling by 62% and rolling recovery of cuttings by over 90%. The field applications in three wells result in the average borehole enlargement ratio below 20% for the Palaeogene formations. The optimized drilling fluid system effectively improves deep well stability in the Linhe block of the Bayan Hetao Basin and technically supports the high-efficient development of the oilfield.