Rheological and yield stress measurements of non-Newtonian fluids using a Marsh Funnel

Accurate and simple techniques for measurement of fluid rheological properties are important for field operations in the oil industry, but existing methods are relatively expensive and the results can be subjective. This is particularly true for measurements of fluid yield stress, which are notoriously difficult to obtain. Marsh Funnels are popular quality-control tools used in the field for drilling fluids and they offer a simple, practical alternative to viscosity measurement. In the normal measurements, a single point (drainage time) is used to determine an average viscosity; little additional information is extracted regarding the non-Newtonian behavior of the fluid.Here, a new model is developed and used to determine the rheological properties of drilling muds and other non-Newtonian fluids using data of fluid volume collected from a Marsh Funnel as a function of time. The funnel results for viscosity and shear-thinning index compare favorably to the values obtained from a commonly-used Fann 35 viscometer. More importantly, an objective, static method for determining yield stress is introduced, which has several advantages over dynamic, extrapolation techniques used for rheometer data.

Research Highlights
► A method for obtaining rheological properties using a Marsh Funnel is presented.
► Excellent fits between the model and data of height versus time are found.
► Data suggest that parameters could be determined explicitly from two initial heights.
► More complicated rheological models may be needed for fluids that do not fit model.
► Ultimate static height in the funnel is a method to objectively estimate yield stress.