导眼与扩眼组合钻进模式在定向井轨迹控制中的应用

定向井由于受诸多因素影响,其实钻轨迹有时并不沿着设计轨道钻进,给钻井施工带来很大挑战。不考虑地层特性、钻井参数、井眼轨迹等影响因素,采用简单实用且可满足工程要求的公式,计算和分析了单弯单稳螺杆钻具组合的理论几何造斜率。研究了井眼及钻具尺寸对造斜率的影响,发现相同条件下小井眼比大井眼更易获得高造斜率。由此提出在造斜率要求较高的井段,可先钻一个小尺寸导眼,再扩眼到设计尺寸的组合钻进模式。以X井为例,证实了在轨迹控制困难的定向井中,采用该组合模式后,满足工程要求且降低作业成本,缩短钻井周期。研究结果为井身结构设计和定向井轨迹控制提供了理论指导和借鉴。

Application of combined drilling mode of pilot hole & reaming in the control of directional well trajectory

Directional wells are affected by a number of factors. Their actual drilling trajectory sometimes is not along the designed track, posing great challenge to drilling operation. This paper does not take into account the influencing factors like formation properties, drilling parameters and wellbore trajectory, but uses simple and practical formula which also satisfies the engineering requirement to calculate and analyze the theoretical geometric build-up rate by combination of single-bend, monostable screw drill assembly. The paper studies the effect of wellbore and drillstring size on the build-up rate and finds that high build-up rate can be obtained more easily in small hole than in large hole under the same conditions. Hence, it is suggested that a small hole may be drilled first where high build-up rate is required, then reaming to the designed size with the combined drilling mode. Take Well X as an example, in directional wells where borehole trajectory is hard to control, the combined drilling mode can meet the engineering requirement, reduce drilling costs and shorten drilling cycle. The research results provide theoretical guide and reference for the design of wellbore configuration and control of directional well trajectory.