Permeability Plugging (PPT)

Purpose

Assess the ability of a drilling fluid or treatment to seal a porous or permeable medium (ceramic disc) under differential pressure conditions. The test is used to evaluate bridging agents, lost-circulation materials, and filtration control additives for reservoir-section drilling.

Equipment

• PPT cell (stainless steel pressure cell)
• Ceramic or synthetic permeable disc (specified permeability, e.g. 1 Darcy)
• Nitrogen pressure source
• Back-pressure regulator
• Graduated collector tube, 10 mL or 25 mL
• Timer
• Heating jacket (if elevated temperature test is required)

Procedure

1. Select and inspect the permeable disc; record its specified permeability.
2. Assemble the cell: place the disc on the lower support screen, seat O-rings, and close the end caps.
3. Fill the cell with well-mixed mud sample from the top inlet.
4. Apply the specified differential pressure across the disc.
5. Start the timer simultaneously with pressure application.
6. Collect filtrate in the graduated cylinder; record volume at 1, 2, 5, 10, 15, and 30 minutes.
7. After the test, disassemble the cell and measure the thickness of any plug formed on the disc face.

Notes

• Report filtrate volume at each time interval and total filtrate at 30 minutes (mL).
• Note whether a competent plug formed and its approximate thickness.
• A rapid initial spurt followed by minimal further filtrate indicates effective bridging.
• Compare results with and without treatment additives to quantify the improvement.