Characterizing the non-Newtonian viscosity of high-solids drilling fluid dispersions by flow loop

Abstract

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. 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. The mixture of solids and drilling fluid results in a highly complex fluid dispersion, typically with a shear-thinning continuum. It is challenging to characterize the viscometric behavior of these dispersions, and such data are limited in the literature. 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. 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. %. The fluid viscosity is reported in terms of power-law parameters, which can be used to predict the pressure drop during real drilling conditions. We found a significant difference in the viscometric response between the drill test and model drilling fluid dispersions. The Shields parameter can capture the influence of solids settling on the measurable pressure losses. An important conclusion is that even model drilling fluid dispersions prepared with geotechnical data from a drill site may have significantly different viscometric characteristics than those relevant during a drilling operation.