HPHT Filtration

Purpose

Measure the filtration characteristics of drilling fluids under high-pressure, high-temperature conditions that simulate downhole environments. The test is critical for evaluating OBM and high-temperature WBM performance where API conditions are insufficient.

Equipment

• HPHT filter press (rated for test temperature and pressure)
• Filter paper (HPHT grade, 3-inch diameter) or ceramic disc, as specified
• Heating jacket and temperature controller
• Nitrogen or CO₂ supply: inlet pressure 1000 psi (6900 kPa), back pressure 500 psi (3450 kPa)
• Graduated cylinder, 10 mL or 25 mL
• Thermometer or thermocouple

Procedure

1. Assemble the clean cell. Place filter paper on the lower screen; seat O-rings and end cap.
2. Fill the cell with well-mixed mud sample, leaving an air gap for expansion.
3. Install the top cap and place the cell in the heating jacket.
4. Apply 100 psi (690 kPa) back pressure to the filtrate side; then heat the cell to the specified test temperature.
5. When temperature stabilises, apply full inlet pressure (500 psi differential) and start the timer.
6. Collect filtrate for 30 minutes, recording volume at the 7.5-minute mark as well.
7. After 30 minutes, safely release pressure from the inlet side first, then the back-pressure side.
8. Allow the cell to cool before disassembling. Recover the filter cake and measure its thickness.

Notes

• The reported HPHT fluid loss equals 2× the 30-minute filtrate volume (because the cell area is half the API cell area).
• Always release inlet pressure before back pressure to avoid forcing fluid back through the cake.
• Follow the equipment manufacturer’s safety procedures — cell contents are at elevated temperature and pressure.
• Record test temperature, differential pressure, and filtrate volume at 7.5 min and 30 min.