One of the major issues in slim-hole drilling and coring operations is the accurate prediction of pressure losses in the annulus, in order to guarantee optimum operating conditions. As has been pointed out in the literature, the small annular clearance and the high rotational speeds of the drillstring are factors which preclude the common assumption of unidimensional axial flow in the annulus, which has commonly been applied for conventional pressure drop computations.

In order to address the effect of rotational speed and eccentricity of the inner core in the laminar flow of power law fluids in the annulus, a finite element scheme was applied. The numerical model showed good agreement with available laboratory data for axial-rotary flows in concentric annuli and axial flows in an eccentric annulus. The analysis revealed the significant effect that the rotational speed and eccentricity of the inner cylinder have on the pressure loss of flows through the annulus.

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