Drilling fluid rheology measurements provide input to flow frictional pressure loss calculations during drilling operations. This study compares the impact of uncertainty of different rheology measurement methods on pressure loss estimation through a series of flow-loop experiments.

The rheological properties of drilling fluids are measured using a high precision Anton Paar rheometer, in-line pipe rheometer and conventional model 35 lab viscometers. The derived viscosity is used to calculate the frictional pressure loss with uncertainty, comparing with in-situ pressure loss observations from flow-loop experiments. The experiments are performed for steady-state, laminar horizontal pipe flow at atmospheric pressure.

The results illustrate the impact different measurement techniques have on the accuracy of the modelled frictional pressure loss. The potential of the pipe rheometer is investigated with respect to use of measured frictional pressure loss data to predict pressure loss in wells and annulus directly. Finally, the effect of variation in the rheological properties have been illustrated on a simulated case downhole.

This study highlights differences in uncertainty range for conventional viscometers in comparison to a high precision rheometer and the propagation of uncertainty to the frictional pressure loss estimation. Quantification of the uncertainty of the modelled frictional pressure is essential information for application of downhole pressure estimation in managing the drilling process. The existing procedure of using conventional viscometers may not be sufficient when accurate pressure control is needed.

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