4.2 Kick Detection While Tripping, Flow Checks & Trip Sheet Interpretation

Tripping is a significant well-control risk because pipe movement and inadequate hole fill can reduce bottomhole pressure. While rotary drilling maintains active mud circulation and continuous annular monitoring, tripping changes wellbore fluid displacement and can introduce surge/swab pressure transients. Under IWCF Level 4 standards, drilling supervisors and engineers must maintain rigorous oversight of trip tank volumetrics, displacement tracking, and flow check procedures.

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1. Trip Tank Architecture and Continuous Monitoring

The trip tank is a small, calibrated vessel used to measure fill and displacement accurately. Know its usable capacity, sensor resolution and line alignment. A narrow tank gives better level-change resolution than a large active pit, but the actual measurement accuracy must be checked rather than assumed.

Continuous and Batch Filling

1. Continuous circulating system: A dedicated pump supplies the top of the annulus and excess returns to the trip tank. The net volume change tracks displacement and possible losses or influx.
2. Batch filling: Fill at the approved interval and record the measured volume. The interval must limit fluid-level loss within the available pressure margin. Do not adopt a fixed stand count without assessing the well.

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2. Metal Displacement vs. Internal Capacity (Dry vs. Wet Tripping)

When a tubular is pulled from the wellbore, the volume of drilling fluid required to keep the hole completely full depends entirely on whether the pipe is pulled dry or wet.

Pulling Pipe Dry

The drillpipe interior drains freely back into the well through the bit nozzles or a functioning float valve. Only the volume of the metallic steel wall is removed from the wellbore. The required hole fill volume equals the metal displacement ($V_{\text{disp}}$): $V_{\text{fill, dry}} = L_{\text{pulled}} \times V_{\text{disp}}$

Pulling Pipe Wet

Wet pipe retains its internal fluid, for example because downward drainage is obstructed or the available differential cannot open a valve. An unported float does not by itself establish wet removal. Verify the actual drainage condition: fluid retained in each stand is removed from the well with that stand. The required hole fill volume equals the sum of the metal displacement plus the internal capacity ($V_{\text{cap}}$): $V_{\text{fill, wet}} = L_{\text{pulled}} \times \left(V_{\text{disp}} + V_{\text{cap}}\right)$

Uniform-Body Displacement Examples

These geometric examples exclude tool joints, upsets and other assembly features. Calculate capacity as ID squared/1029.4 and metal displacement as(OD squared-ID squared)/1029.4 in bbl/ft. For an actual trip, use the applicable manufacturer/string data, including connection volumes where required.

For the 5 in body with 4.276 in ID, pulling wet instead of dry removes an additional 0.01776 bbl/ft of internal fluid, or 17.76 bbl per 1,000 ft. Failing to replace that fluid reduces the pressure barrier.

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3. Trip Sheet Compilation and Real-Time Interpretation

A calibrated trip sheet must be calculated prior to initiating any trip out of the hole (POOH) and updated continuously stand-by-stand as tubulars are pulled.

Mathematical Formulation of Trip Sheet Tracking

For each approved recording interval, use displacement per foot D equal to metal displacement for dry pipe or closed-end displacement for wet pipe:

1. Theoretical Fill ($V_{\text{theo}}$): $V_{\text{theo}} = \sum \left(L_{\text{stand}} \times D\right)$
2. Measured Fill ($V_{\text{meas}}$): Recorded directly from the calibrated trip tank level gauge.
3. Stand Discrepancy ($\Delta V$): $\Delta V = V_{\text{theo}} - V_{\text{meas}}$
4. Cumulative Discrepancy ($\Delta V_{\text{cum}}$): $\Delta V_{\text{cum}} = \sum \Delta V$

Representative Trip Sheet: Swabbing Detection Example

Well Parameters: Pulling 5-inch drillpipe dry ($V_{\text{disp}} = 0.0075\text{ bbl/ft}$, $0.675\text{ bbl/stand}$ at $90\text{ ft/stand}$). Baseline overbalance = $180\text{ psi}$.

4. Flow Check Protocols and Best Practices

A flow check observes whether the well flows with pumps stopped and pipe stationary. It assesses current behaviour; a negative check does not prove that no swabbed influx is present.

Operational Checkpoints

Follow the approved programme for checks before pulling, during the early trip, at the casing shoe and before the BHA enters the BOP. Stop and check following a drilling break or unexplained displacement change. Verify that the tubular across each relevant preventer is suitable for the planned containment action.

Flow-Check Execution

1. Pick up and space out: Place tool joints clear of the designated ram sealing/shearing positions, with the required connection accessible for a safety valve.
2. Stop the pumps and pipe movement: Use the approved monitoring line-up, normally the calibrated trip tank where available.
3. Observe and interpret: Compare flow/volume with the normal flow-back fingerprint for the prescribed check period. Unexpected sustained flow requires prompt containment; do not wait for a universal 10-15 minute minimum.
4. Assess a negative check: Investigate the original warning or fill discrepancy before resuming. If swabbed fluid may remain, assess a controlled return to bottom and circulation with the required precautions.

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5. Tripping With Partial Lost Circulation

When pulling pipe through a formation experiencing partial lost circulation (e.g., losing $15\text{ bbl/hr}$ to micro-fractures), distinguishing between normal seepage losses and a swabbing kick presents a sophisticated well control challenge.

Tripping Management Protocol

1. Assess the loss trend and barrier: Establish the measured loss rate over a known interval and determine whether tripping can safely proceed. For example,15 bbl/hr is 0.25 bbl/min; the rate may change with pressure or movement.
2. Account for volumes: Expected fill equals the dry/wet pipe-displacement volume plus measured losses during the interval, with other transfers and slug effects accounted for separately. A deviation requires investigation and the approved check/containment response.
3. Slug only under the approved plan: A denser slug can lower the fluid level inside the upper pipe through the U-tube effect so those stands pull dry. It does not eliminate annular swabbing. Verify slug density/volume, losses and resulting fluid levels before relying on dry-pipe displacement.
4. Maintain and monitor the hole: Use accurate measured filling and suitable trip speeds. Losses can conceal influx, so do not interpret a lower apparent loss rate or a static surface level as proof of safety.