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rheology

Marsh Funnel Viscosity

Purpose

Provide a quick, field-level indication of drilling-fluid viscosity on a routine basis using the Marsh funnel. Results are expressed in seconds per quart.

Equipment

  • Marsh funnel (standard API geometry)
  • Graduated measuring cup, 1000 mL
  • Stopwatch or timer

Procedure

  1. With a finger over the outlet tube, pour a freshly collected and stirred mud sample through the screen into the clean, dry funnel until the fluid level reaches the bottom of the screen (the 1500 mL mark).
  2. Immediately remove the finger from the outlet tube and simultaneously start the stopwatch.
  3. Measure the time required for 1 quart (946 mL) of mud to flow into the measuring cup.
  4. Stop the timer when the fluid level in the measuring cup reaches the 946 mL mark.

Notes

  • Report funnel viscosity to the nearest second. Example: “Marsh Funnel Viscosity = 42 sec/qt”.
  • The fresh-water baseline at 70 °F (21 °C) is 26 ± 0.5 seconds.
  • Keep the funnel screen clear of large cuttings or debris that may obstruct flow.
  • Test should be performed immediately on a freshly collected sample to minimise temperature and settling effects.