TITLE:
Estimating Water-Based Mud Rheology from Marsh-Funnel Drainage Using Capillary-Flow Analysis
AUTHORS:
Mohamed Omer Mohamed Elnaeem
KEYWORDS:
Marsh Funnel, Water-Based Mud, Capillary-Flow Analysis, Rheology, Power-Law Model, Gel-Strength Indicator
JOURNAL NAME:
World Journal of Engineering and Technology,
Vol.14 No.3,
June
22,
2026
ABSTRACT: The Marsh funnel is widely used at the rig site as a rapid drilling-fluid quality-control tool, but its conventional output—a single drainage time—does not provide full rheological characterization. This study evaluates whether Marsh-funnel drainage data can be converted into rheological information for water-based drilling muds using capillary-flow analysis, funnel-geometry variation, and statistical modeling. Nine water-based mud samples, including gel mud, KCl-polymer mud, and KCl-silicate mud, were tested with a 6-speed rotational viscometer and six funnel geometries. Drain-volume/time data were collected for immediate drainage and after 1-, 5-, and 10-minute waiting periods. Wall shear stress and corrected wall shear rate were calculated using pressure-driven-flow concepts and Weissenberg-Rabinowitsch correction, and funnel-derived rheograms were compared with 6-speed viscometer behavior. Power-law behavior described the mud samples more consistently than the Bingham plastic model, with an average R2 of 0.956 compared with 0.773 for Bingham fitting. Funnel geometry affected the reliability of funnel-derived rheograms; larger orifices reduced orifice resistance and improved fluid-behavior expression, whereas the smallest orifice produced poor or invalid responses for viscous samples. Multivariable regression linked the consistency index primarily to solid content and funnel drainage-time ratios, whereas the flow-behavior index required consistency-index information for reliable prediction. A gel-strength indicator based on the area change between apparent-viscosity/shear-rate curves after static waiting detected gel response in 94 of 145 valid attempts, or 64.8%. The results support Marsh-funnel use as a supplementary field rheometry tool when calibrated against conventional viscometer data, although standalone deployment requires further validation across temperature, oil-based muds, and broader field mud systems.