及时封堵钻井液体系在低承压地层中的优化与运用

Optimization and application of plugging immediately drilling fluid system in low-pressure formation

随着超深井钻井技术的成熟,钻探目的层越来越深,钻进中穿越裸眼井段长度不断增加,超过1000 m的裸眼钻进中因地层跨度大,地层压力系数差异大,若钻井液选择不当,易造成低承压地层井漏、较高承压地层垮塌、井壁失稳等复杂情况。针对同一裸眼段中不同层位所对应的不同地质情况,优选钻井液性能对顺利完钻至关重要。以四川盆地西北部双鱼石—河湾场构造ST2井为研究对象,针对该井钻进中穿越中侏罗统须家河组—中三叠统雷口坡组大段裸眼地层,地层承压能力差异大,井下情况复杂,力求寻找一种性能稳定,适用于同一裸眼段中不同层位的钻井液体系。在综合钾聚磺钻井液体系和及时封堵钻井液(JSF)体系的基础上,通过优化钻井液配方、调整钻井液性能,合理使用固控设备等方面入手,优化改进了传统的JFS体系,在ST2井三开钻进中取得显著效果。现场应用表明:优化的JSF体系在长裸眼井段中有着良好的稳定井壁、携砂、润滑等特性,降低了井下复杂的发生率,缩短了施工周期,具有明显的经济效益。

As the ultra deep well drilling technologies get mature, drilling operation targets at deeper layers, and correspondingly the drilling length of open hole interval increases. During the open hole drilling over 1000 m long, the formation span is large and the formation pressure coefficient varies greatly. Therefore, improper application of drilling fluids may lead to several complexities, suchas circulation loss in low-pressure formation, collapse of high-pressure formation and borehole instability. In order to carry out well drilling smoothly, it is crucial to optimize the performance of drilling fluid according to the geological characteristics of horizons in the same open hole interval. In this paper, Well ST2 at the Shuangyushi-Hewanchang structure in northwestern Sichuan Basin was tak- en as an example. It runs through a long open hole strata of Middle Jurassic Xujiahe Formation-Middle Triassic Leikoupo Formation,where downhole situations are complex with larger differences in formation pressure, so it is necessary to search for a drilling fluid system that is suitable for different horizons in the same open hole interval. Based on the combination of potassium polysulfonate drilling fluid system and JFS system, the traditional JFS system was improved by optimizing the formula of drilling fluid, adjusting the performance of drilling fluid and using the solid control equipment rationally. The optimized JFS system was successfully applied in the third section of Well ST2. It is indicated that this optimized JFS system is capable of borehole stabilization, proppant carrying and lubricating in long open hole intervals. With this system, the downhole complexity probability is reduced, and the operation time is shortened, corresponding to remarkable economic benefits.