Rheological analysis of drilling fluid using Marsh Funnel

•Consistency plot from Marsh Funnel readings.•Yield point, apparent viscosity and plastic viscosity from Marsh Funnel.•Rheology of polyethylene glycol based drilling fluid.•Comparison of Marsh Funnel and Fann 35 viscometer rheology.

In this study, Marsh Funnel is used to determine the rheological properties, namely, yield point, apparent viscosity and plastic viscosity of drilling fluid. Funnel drainage volume and corresponding drainage time are two measured variables for this analysis. Drainage volume is used to predict funnel wall shear stress whereas drainage rate is used to estimate funnel wall shear rate. The predicted shear rate is independent of rheological models. Yield point is calculated from remaining volume of fluid in the funnel at the end of the experiment under no flow condition whereas apparent viscosity and plastic viscosity are determined from the funnel consistency plot. Synthetic crude oil and the suspension of several drilling fluid additives (e.g., bentonite, polyethylene glycol–sodium chloride and polyethylene glycol–sodium chloride–bentonite) with practical importance have also been used to determine yield point, apparent viscosity and plastic viscosity using the Marsh Funnel readings. Finally, the Marsh Funnel rheological results are also compared with the Fann 35 viscometer results.