Well Intervention Pressure Control
Well Intervention Pressure Control
This domain tests pressure containment and barrier management during interventions in live wells, including wireline, slickline, coiled tubing, snubbing, stripping, and pumping. Level 2 questions focus on pressure-control equipment, equipment ratings and length, and the forces that well pressure creates on a toolstring or pipe.
Core rules and concepts
- Use at least two independent barriers. The fluid column and a downhole or mechanical barrier may provide primary containment; the pressure-control stack provides secondary containment.
- A typical wireline stack includes a master valve, wireline BOP, lubricator, and stuffing box or grease injection head. Test and verify the stack before breaking containment.
- The lubricator must be long enough to house the toolstring with the BOP closed, and its pressure rating must exceed the maximum anticipated shut-in wellhead pressure.
- Wireline BOP rams may be blind, shear, or pipe/slip types. Coiled-tubing stacks use a stripper plus slip, pipe, blind, and shear rams.
- Snubbing is used when well pressure would push pipe or tubing out of the well; stripping is moving pipe through closed rams while maintaining a seal.
- Track displacement and bleed-off volumes with a trip sheet so that excessive bleed-off does not remove the hydrostatic overbalance.
Worked example
A 1.875-in OD slickline toolstring is held in a lubricator with 2,000 psi shut-in wellhead pressure. Tool OD area = π/4 × 1.875² = 2.76 in². Upward force from pressure = 2,000 × 2.76 = 5,520 lbf. If the toolstring weighs only 900 lbf, the pressure force exceeds its weight, so the string is light and would be pushed upward unless restrained. The winch, rope socket, and hold-down method must control this load; do not open the well until the stack and procedure are rated for it.
Traps that cost marks
Using lubricator ID instead of tool OD; ignoring pressure-induced upward force; choosing a lubricator that is too short for the toolstring; relying on one barrier; and opening the well before the stack has been tested.