Viscosity describes a substance’s resistance to flow. High-viscosity drilling mud is typically described as “thick,” while low-viscosity mud is characterized as “thin”. In the oilfield, the following terms are used to describe drilling fluid viscosity and rheological properties. Two viscosities that will be described in this section are Funnel Viscosity and Plastic Viscosity.
The funnel viscosity is timed in seconds of drilling mud flowing through the Marsh Funnel Viscosity. The Marsh funnel is easy-to-use equipment that is used to quickly check viscosity of the mud. The Marsh funnel is dimensioned so that the outflow of time of one quart of freshwater (946 cc) at a temperature of 70 F ± 5 F (21 C ± 3 C) in 26 ± 0.5 seconds.
Figure 1 – Marsh Funnel Continue reading