摘要
在中国,页岩气储层长水平井段钻进中普遍采用油基钻井完井液,钻进过程中时常发生井壁垮塌和漏失,不得不频繁处理井下事故,导致页岩段钻井速度慢,浸泡时间长,引发严重的储层损害问题。为了探究油基钻井完井液对页岩储层的损害机理及防治策略,以四川盆地志留系龙马溪组和寒武系牛蹄塘组页岩为研究对象,开展了页岩储层敏感性评价、油基钻井完井液静态和动态损害评价系列实验。结果表明,油基钻井完井液滤液对裂缝岩样的损害率为63.5%～99.9%,体系动态损害率为49.0%～87.2%,综合损害程度为中等—强。结论认为:固相侵入、油相圈闭损害、碱敏损害、流—固耦合强化的应力敏感损害是主要的损害方式;及时高效封堵裂缝、降低滤失量、控制合理的pH值和正压差,并与井眼轨迹优化设计相结合既是强化页岩井壁稳定的技术对策,也是提高油基钻井完井液保护页岩气储层能力的重要途径。
Currently, oil-based drill-in fluids have been widely used in China to prevent the frequent collapse and leakage of well borehole during long lateral horizontal drilling targeting organic-rich shale reservoirs. However, wellbore instability still happens fre- quently during drilling process. When such complicated downhole drilling accidents are dealt with, drilling speeds and trips will be slowed down and the reservoir rocks will be soaked for a long time, resulting in significantly serious formation damage. Therefore, this paper aims to explore the damage mechanism of oil-based drill-in fluids to shale reservoirs and to acquire prevention strategies. Collecting gas shale cores from the Silurian Longmaxi and Cambrian Niutitang Fins in the $ichuan Basin, we made an evaluation a- nalysis of shale formation sensitivity and conducted experiments of oil-based drill-in fluidsr static and dynamic damage to shale for- mations. Results showed that the static damage rate ranged from 63.5 to 99.9 ~/00, while the system dynamic damage rate from 49.0 to 87.2%, which means a moderate to strong damage as a whole. It was considered that major damage factors include solid phase intru- sion, alkali sensitivity damage, oil phase trapping damage, and stress sensitivity damage enhanced by fluid-solid interaction. On this basis, we presented that combining efficient fracture plugging, pH value optimizing, filtration volume and positive pressure differen- tial control with an optimal well trajectory design can not only strengthen the shale wellbore stability, but provide an effective way to mitigate the formation damage of oil-based drill-in fluids.
出处
《天然气工业》
EI
CAS
CSCD
北大核心
2013年第12期99-104,共6页
Natural Gas Industry
基金
国家重点基础研究发展计划(973计划)(编号:2010CB226705)
国家科技重大专项(编号:2011ZX05018-005-003)
关键词
页岩
裂缝(岩石)
岩样
油基
钻井完井液
储集层损害
保护措施
shale, fracture （rock） , core, oil-based drill-in fluids, reservoir damage, reservoir protection measure
