Annular and Ram-to-Ram Stripping

Purpose and prerequisites

Stripping moves pipe through closed well control equipment while retaining pressure containment. It can be used to return a string toward bottom after an influx is detected off bottom, so that the influx can be circulated out through the approved route. It is a supervised pressure-and-volume operation, not ordinary tripping with a BOP accidentally left closed. The string must be suitable for movement through the selected elements and the pressure, force, displacement and gas-migration limits must be known.

Before stripping, secure the well, record pressures and influx information, establish the required internal string barrier and prepare the trip tank, choke and approved monitoring route. Confirm annular or ram stripping capability, closing-pressure instructions, tool-joint positions, pressure ratings and the pipe's tendency to move upward or downward under pressure. A lightweight string under high pressure can experience an upward force requiring qualified handling equipment. Do not assume pipe weight alone will control movement.

Volume balance preserves bottomhole pressure

Pipe entering the closed well displaces fluid. If that displaced volume has no controlled outlet, pressure can rise and load the weak formation. If too much is released, bottomhole pressure can fall and admit more influx. Gas migration can change the required pressure independently of pipe movement. Keep records of pipe displacement and migration-related bleed volumes separately, with the approved reference pressure and margins.

For a training case with closed-end displacement of 0.0240 bbl/ft, stripping 90 ft into the well displaces 2.16 bbl. That is the pipe-entry volume to account for under the stated geometry. If 3.00 bbl is actually collected, the unexplained 0.84 bbl requires investigation; it cannot automatically be labelled gas migration. The correct displacement may change at a BHA or when an internal valve configuration changes. Use the agreed displacement factor for each item and the actual tank readings.

Annular stripping

A qualified annular element may permit tool joints to pass while maintaining a seal. The closing pressure should be selected from the manufacturer's data for the well pressure, tubular size and stripping duty. Excessive closing pressure accelerates element wear and can damage the tubular; insufficient pressure permits leakage. Adjust at the specified times and monitor seal performance. The presence of an annular BOP alone does not prove every tool joint, cable or BHA can pass under pressure.

Move at the instructed slow rate and coordinate with the choke operator to account for displacement while preserving the required bottomhole pressure. Watch the pressure trend, tank volume, pipe load and leakage. Pause at planned positions for checks. A controlled leak past an element is acceptable only if explicitly part of the approved stripping arrangement and safely routed; unplanned gas at the drill floor is a failure requiring the contingency response. Never treat packing wear as a reason to continue at higher speed.

Ram-to-ram stripping

Ram-to-ram stripping uses appropriately spaced, qualified ram sets to move a tool joint through the stack while retaining at least the required containment. The sequence depends on the actual stack drawing and pipe spacing. Tool joints must clear the ram that is about to close, and the chamber between rams must have a controlled equalising and bleed route. Before opening a barrier exposed to differential pressure, equalise as instructed; before transferring containment, verify the receiving ram is closed and sealing.

In a conceptual cycle, one suitable ram contains the well while the other is open to allow the joint to move into the chamber. Stop at the documented space-out point, close and verify the receiving ram, then equalise the isolated chamber for the next transfer before opening the first ram. Continue the prescribed cycle as the joint passes. This explanation shows the barrier-transfer principle; the exact valve positions and order come from the installed system's procedure. Opening both rams together would defeat that principle.

Limits and complications

Stripping can be limited by annular wear, non-sealable diameters, inadequate ram spacing, tool joints, insufficient closing pressure, pressure-induced pipe force, internal influx, hydrates, restrictions and weak-point pressure. A non-shearable BHA may remove an emergency closure option while crossing the stack. Identify it before movement and use the approved risk controls. Pipe loads and hang-off ratings must be qualified for the actual ram and joint.

Gas in a horizontal section may migrate little until swept into a vertical interval. Moving the string and displacing fluid can change its location and pressure effect. Do not assume the original shut-in pressure remains an adequate reference throughout an uncontrolled sequence. The supervisor directs the combined stripping and volumetric plan and the eventual circulation method.

First actions when the plan departs

If pressure, leakage, displacement or load deviates from the plan, stop pipe movement and communicate. Secure the well with the available approved barrier and retain the record of cumulative movement and collected fluid. Do not reset tank totals to conceal a mismatch. A safe stopping point is part of the plan, as is the alternative if an annular or ram fails. Reaching bottom is useful only if the operation preserves containment and the formation pressure window on the way there.

Stripping controls