Snubbing Operations
Snubbing Operations tests running and pulling pipe while the well is under pressure. It covers BOP stack arrangement, snubbing versus stripping, force calculation, and pipe limits.
Core rules
- Snubbing runs pipe into a live well; stripping moves pipe through a closed annular or BOP without rotation. Both require a rated stack and a planned sequence.
- A typical snubbing stack includes annular preventers, slip rams, pipe rams, and blind/shear rams. Confirm the sequence before starting.
- Calculate the upward force from well pressure on the pipe cross-section, then compare with pipe weight and buoyancy. The difference determines whether the pipe must be snubbed or can be run.
- Do not exceed pipe buckling, tension, or collapse limits. Use a guide and controlled snubbing speed.
- Barriers are the BOP rams and annular; the pipe is not a barrier.
Worked example
2.875 in OD pipe is exposed to 3,000 psi. Cross-sectional area = π/4 × 2.875² ≈ 6.49 in². Upward force = 3,000 × 6.49 ≈ 19,500 lbf. If 1,000 ft of 6.5 lb/ft pipe weighs 6,500 lbf, the net upward force is about 13,000 lbf. The pipe must be snubbed, not simply run, and the snubbing unit must be rated above that force with a margin.
Traps
- Ignoring buoyancy or using nominal weight without buoyancy.
- Using the wrong BOP sequence.
- Forgetting that tool joints and collars change the seal diameter.
- Snubbing damaged or bent pipe.
- Treating the pipe as a barrier.