Excessive torque and drag is a major challenge in drilling and completion of extended-reach wells and horizontal wells with high degree of 3D geometry. Torque and drag modeling is regarded as an invaluable process to assist in well planning and to predict and prevent drilling problems. Some wells can be drilled, but may not be completed due to high friction.

Most of today’s torque/drag models are based on the work of Johancsik et. al. (1984) and Sheppard et. al. (1987), while a more comprehensive model is derived by Mitchell and Samuel (2009).

If we assume the drill-string as the elastic-solid material, then a solid material can develop shear stresses. In this study the effect of shear forces on torque and drag modeling has been analyzed. This force is usually ignored in industrial softwares. The effect of disregarding bending stiffness in the equilibrium equation of the drill-string has been stated shortly with some field examples.

Moreover the effect of stream-thrust force on the axial force has been assessed. One part of this force is hydraulic force acting on the closed-end pipe when it is stabbed into the wellbore or by larger diameter pipes when the string is pulling out of the hole. The resulting force together with pressure-area force which is a force resulting from different pressures inside and outside of the pipe has been put together in one equation and it will affect friction in the wellbore that has been addressed here. In other words effective force which is the summation of the axial force and stream-thrust force will be replaced by axial force in the force balance equations. The above-mentioned factors have been implemented in a field case-study. Hence the importance of these forces in the torque-drag modeling in the wellbore has been identified.

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