Understanding Torque and Drag: Best Practices and Lessons Learnt from the Captain Field's Extended Reach Wells

Abstract

Abstract This paper describes how torque and drag (T&D) analysis was used to successfully drill extended reach (ERD) wells in the Captain field in the North Sea. The issues and best practices associated with using this basic real-time drilling technique, particularly on Captain subsea development wells drilled from 2000 to 2003, are explained. The paper also explains the tactics used in overcoming issues such as how far could we drill and the associated risk. The applicability of available T&D reduction technologies and why many of them were eliminated as possible solutions reinforced the criticality of good T&D analysis on this project. The Captain subsea wells have the highest aspect ratio (unwrapped displacement [UD] / true vertical depth [TVD]) ever for development wells drilled and completed from a floating vessel. Although the wells are short in displacement for ERD wells, the shallow nature of the reservoir requires the application of T&D analysis, which has been at the core of good ERD drilling principles and practices for some time. This paper outlines what T&D analysis is and why it is important. The design of the bottomhole assembly (BHA) and drilling string, drilling string buckling, friction factor (FF) analysis, casing sanding considerations, trajectory design, and wellbore tortuosity all must be considered in applying this basic technique to field operations. Other issues such as why it is often misunderstood or badly applied, the importance of calibration with offset data, and conditions that effect FF determination are explained.