Evaluation of drag minimum for catenary curve susing approximate catenary trajectory and equivalent build up section

摘要

For an extended reach drilling simulation, many important techniques are required. Torque and drag prediction is one of them. There is an opinion that catenary trajectory can minimize drag. However, as drag is accumulated upward, drag is affected not only by bending rate but by hook load and inclination angle at lower end of catenary. For a temporary evaluation whether drag of catenary is the minimum or not, two types of trajectory are compared through simulation study. One is an apprximate catenary trajectory which composed of multiple build up section with different bending rate, and another is equivalent build up section which has the same inclination angle and lower end as the f ormer. The following findings are obtained. (1)Drag of approximate catenary trajectory does not remarkably decrease comparing with that of equivalent build up section. (2)When drag of catenary trjectory decreases comparing orginal build up section, the major decrease of drage amy be contributed to the connecting downward tangent section. (3)In this sense, the effect of catenary for drag decrease may be said that catenary can increase inclination angle, since high inclination angle can decrease drag over downward tangent section.