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filtration

API Filtration

Purpose

Determine the fluid-loss characteristics of water-based drilling fluids under standard API conditions (ambient temperature, 100 psi differential pressure, 30-minute test). The filtrate volume and filter-cake thickness indicate the mud’s ability to control formation invasion.

Equipment

  • API filter press (standard cell)
  • Filter paper (API Spec 13B-1 grade)
  • Nitrogen or CO₂ pressure source regulated to 100 psi (690 kPa)
  • Graduated cylinder, 10 mL or 25 mL
  • Timer

Procedure

  1. Assemble the clean, dry filter press cell. Place a filter paper on the screen at the base.
  2. Pour the well-mixed mud sample into the cell, leaving a small air gap at the top.
  3. Close the cell and place it in the filter press stand.
  4. Apply 100 ± 5 psi pressure and simultaneously start the timer.
  5. Collect filtrate in the graduated cylinder for exactly 30 minutes.
  6. Record the total filtrate volume in mL.
  7. After 30 minutes, release pressure carefully, disassemble the cell, and remove the filter cake.
  8. Rinse the filter cake gently with water and measure its thickness with a ruler.

Notes

  • Report API fluid loss as mL/30 min and filter-cake thickness in mm (or 1/32 in).
  • If significant filtrate is collected in the first minute, report the 7.5-minute value doubled as an approximation of the 30-minute value.
  • Ensure the cell, screen, and O-rings are clean and undamaged before each test to avoid leaks.