Monitoring a Well Prior to Removing the BOP Stack
Monitoring a well prior to removing the BOP (blowout preventer) stack is a critical operation that requires isolation, certainty prior to barrier removal. In the event that flow is observed before stack removal, kill methods will be limited.
The following incident from IOGP* describes a familiar method of handling an influx behind casing where standard circulation techniques are not available. The Lubricate and Bleed method is one approach to managing an influx while waiting on cement (WOC), swapping out gas at surface for overbalanced fluid while managing pressure on the well. [The lubricate and bleed procedure is the way to remove the gas when the circulation is impossible to conduct. The basic theory is the same as Volumetric Well Control Method but a reverse process.]
The incident description helps highlight the importance of understanding fundamental well control techniques beyond standard circulation techniques and demonstrates the relevance of alternative kill methods.
Lubricate and bleed influx behind cemented casing
The well section was successfully drilled through drawn-down sand formations, the casing was run to setting depth and the subsequent cement job was pumped without issue.
After WOC to reach 50 psi compressive strength, the well, which was being monitored with the trip tank, showed a quick 6.8 bbl gain. The well was secured by closing the BOP. The well was monitored while cement continued setting to >500 psi compressive strength; initial SICP was 230 psi and increased to a stable value of 310 psi.
The well was killed using the lubricate and bleed method of well control, reducing SICP from 310 psi to 0 psi with 18 L&B cycles using 10.1 ppg NAF mud: 2 bbls/cycle lubricated (45 minutes wait time after each lubrication), 20 psi gas bled/cycle (30 minutes of monitoring after each bleed), total 34.75 bbls lubricated.
What went wrong?
Charged formation and potentially insufficient lead cement slurry quality.
Corrective actions and recommendations
Continued focus on well control during and after cementing operations with special attention to WOC and flow checking prior to the removal of BOP for wellhead installations.
The incident represents an example of why it should always be assumed that a well is capable of flow.
Certain regions have historically seen inconsistency in cement material quality; the incident highlights the importance of the quality of cement materials.
This blog post content is taken from the Safety Zone, IOGP* (International Association of Oil & Gas Producers) Well Control Incident Lesson Sharing report 20-8.
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