Swab kick due to limited trip margin in an appraisal well with geological uncertainties
IOGP Well Control Incident Lesson Sharing #24-1
After drilling 8-1/2" section to coring point, well was circulated clean and flow checked stable. Pumped Out Of the Hole to 100m inside 9 7/8" casing shoe and flow checked stable. Pulling Out Of the Hole at controlled speed another 250m with proper displacement. Pumped slug and continued to POOH dry at controlled speed to 2100m - observed incorrect displacement on the last stands (80lts gain). Flow checked on trip tank with 0.8 m3 gain observed. Shut in well: SICP 175 psi - SIDPP 65 psi. Cumulative gain 1.8 m3. Stripped back to bottom (3500m). Controlled well with drillers method, evacuated influx - 16% max gas (downstream MGS) - observed well stable. Displaced well to heavier mud 1.38sg for trip margin.
The IOGP Wells Expert Committee/Well Control Incident Subcommittee believes that this incident description contains sufficient lessons to be shared with the industry. We further encourage the recipients of this lesson sharing to share it further within their organization.
What happened?:
After drilling 8-1/2" section to coring point, well was circulated clean (MW 1.36sg; max gas 0.7%) - Flow Check stable. Pumped OOH to 100m inside 9 7/8" casing shoe - Flow check stable. POOH at controlled speed another 250m - proper displacement. Pumped slug and continued to POOH dry at controlled speed to 2100m - observed incorrect displacement on the last stands (80lts gain). Flow checked on trip tank with 800 lts gain observed. Shut in on LAP - CL 150psi / KL 175 psi / SPP 65 psi. Observed pressures behaviour, confirmed kick diagnosis (CL 225psi / Kill Line 250psi / SIDPP 75 psi - Cumul gain 1.8m3). Stripped back BHA to bottom (3500m down). Controlled well with drillers method, evacuated influx - 16% max gas (downstream MGS) - observed well stable. Displaced well to heavier mud 1.38sg for trip margin.
What Went Wrong?:
- Swab kick.
- Geological uncertainties in appraisal well.
- Narrow mud weight window, lack of trip margin.
Corrective Actions and Recommendations:
- Displace heavier mud for trip margin.
- Extended flow check before POOH.
- Pay attention to mud parameters.
- Transfer and capture experience to new wells in surrounding area.
- Increase trip margin for next coring ops.
safety alert number: 362
IOGP Well Control Incident Lesson Sharing http://safetyzone.iogp.org/
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