Mud Weight (Density)

Purpose

Determine the density (weight) of the drilling fluid — the primary control on hydrostatic pressure — using a mud balance. Applicable to water-based mud, oil-based mud, and completion or work-over fluids.

Equipment

• Mud balance with cup, lid, and knife-edge beam
• Base stand or carrying case
• 1-qt (946 mL) graduated measuring cup
• Thermometer: 32 to 220 °F (0 to 104 °C)

Procedure

1. Place the base stand or carrying case on a flat, level surface.
2. Collect a freshly agitated fluid sample.
3. Measure and record the temperature of the sample.
4. Transfer the sample to the clean, dry mud balance cup.
5. Tap the side of the cup gently with the lid to break out any trapped air or gas.
6. Wipe all excess mud from the outside of the cup; apply and seat the lid.
7. Wipe all mud from the knife edge and rider area of the beam.
8. Place the beam in the base stand with the knife edge resting on the fulcrum.
9. Move the rider along the beam until the level bubble is centred when viewed through the levelling glass.
10. Read mud weight directly from the scale at the rider’s inner edge.

Notes

• If trapped air or gas is suspected, use a pressurised fluid-density balance for a more accurate reading.
• Calibrate the instrument with fresh water (8.33 lb/gal / 1.00 sg / 1000 kg/m³) before use.
• Report mud weight to the nearest 0.1 lb/gal (0.01 g/cm³ or 5 kg/m³).
• Record both temperature and mud weight on the mud report.