Annular frictional pressure losses for drilling fluids

In the paper it is demonstrated how a Herschel-Bulkley fluid model, where the parameters are selected from relevant shear rate range of the flow and are parametrically independent, can be used for pressure loss calculations. The model is found to provide adequate pressure loss predictions for axial flow in an annulus where the inner cylinder does not rotate. It is described how one can simplify a slot model approximation of the annulus pressure loss using the Herschel-Bulkley fluid model (Founargiotakis model). This simplified model gives approximately the same accuracy as does the full Founargiotakis model. It is shown that use of such a parallel plate model gives reasonably good fit to measured data on laminar flow of oil-based drilling fluids if the viscous data are measured at relevant shear rates for the flow. Laboratory measurements indicate that use of the simplified pressure loss model is also valid for turbulent flow. However, the predictions should be adjusted for the surface roughness in the well.