Abstract
Torque and drag analysis has been used for more than ten years to drill wells ‘on paper’. Representations of the drillstring and bottomhole assembly (BHA) that do not include the individual component stiffness have been used with some success in analyzing and preventing problems in extended reach drilling. As curve rates have increased in directional wells and the trajectories themselves become more complex, the effects of the previously neglected stiffness have led to errors in the sideforce calculations that underpin all torque and drag analysis. Finite-element analysis can solve this problem. Additionally, tortuosity can be added to provide a rippled effect to a well trajectory design that simulates the micro dog-legs that occur in the drilled well, enabling more realistic bounds to be placed on the drag and torque losses, and the forces experienced by the drillstring. Tortuosity also allows more accurate modeling of the side forces between the casing and drillpipe, critical to extended reach well design. This is illustrated using a well with a deep kick-off point from the Gulf of Mexico.
A case study based on wells drilled from the Hibernia platform is used to illustrate how the model has been utilized to aid planning decisions and reduce costs.
