High Accuracy Determination of Rheological Properties of Drilling Fluids Using the Marsh Funnel

Abstract

Efficient and safe drilling operations require precise determination of rheological properties in drilling fluids, encompassing dynamic viscosity for Newtonian fluids, and apparent viscosity, plastic viscosity, and yield point for non-Newtonian fluids. Conventional viscometers like vibrating wire, ZNN-D6, and Fann-35 offer high accuracy but are limited by cost and complexity in small-scale industries and labs. To address this, our research presents a novel mathematical model based on the Herschel-Bulkley model, aiming to accurately characterise drilling fluids' rheological properties using the Marsh funnel as an alternative device -- an economical, operator-friendly, and power-independent equipment. Drawing inspiration from seminal works by Li et al. (2020), Sedaghat (2017), and Guria et al. (2013), this innovative framework establishes a universal inverse linear relationship between a fluid's flow factor and final discharge time. For any fluid, it utilises its density and flow factor (or final discharge time) to determine all its rheological properties. Specifically, it evaluates dynamic viscosity for Newtonian fluids, apparent viscosity, plastic viscosity, and yield point for weighted non-Newtonian fluids, and apparent viscosity for non-weighted non-Newtonian fluids, with average systematic errors (against Fann-35 measurements) of 0.39%, 3.52%, 2.17%, 18.38%, and 5.84%, respectively, surpassing the precision of alternative mathematical models found in the aforementioned literature. Furthermore, while our framework's precision in plastic viscosity and yield point assessment of non-weighted non-Newtonian fluids slightly lags behind the framework of Li et al. (2020), it outperforms the model of Sedaghat (2017). In conclusion, despite minor limitations, our proposed mathematical model holds huge promise for drilling fluid rheology in petroleum, drilling, and related industries.