The Shields parameter can capture the influence of solids settling on the measurable pressure losses. We found a significant difference in the viscometric response between the drill test and model drilling fluid dispersions. The fluid viscosity is reported in terms of power-law parameters, which can be used to predict the pressure drop during real drilling conditions. In this work, we characterize the viscometric properties of a drill test and model drilling fluid dispersion in a custom-built flow loop with solid concentrations up to 45 wt. It is increasingly important to understand and accurately model the viscosity of these dispersions since high drilling speeds increase the drilling fluid flow rate, approaching the pressure limits that borehole walls can withstand before failure. It is challenging to characterize the viscometric behavior of these dispersions, and such data are limited in the literature. The mixture of solids and drilling fluid results in a highly complex fluid dispersion, typically with a shear-thinning continuum. A significant challenge to increasing speed in horizontal directional drilling is pressure and flow rate management of drilling fluids circulating into and out of the borehole, removing solids cut free by the drill bit. Increasing the speed of drilling operations is of commercial and military interest for transportation infrastructure as well as rapid installation of underground utilities in urban settings and over long distances.
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