What happened:
During a cementing operation, the flow line (used to direct returns from the wellbore to the shaker or pit system) became packed off—essentially blocked or restricted. As a result, returns had nowhere to go, and the cement being pumped had to find an alternate path. With no outlet, it flowed up through the BOP stack and into the cellar, which is the pit around the wellhead.
Possible Causes:
- Flow line restriction or blockage:
Cement or drilling solids buildup.
Mechanical obstruction (valve closed, line collapsed, etc.). - Poor monitoring or miscommunication:
Mud returns not being closely monitored.
Late response to pressure build-up. - Improper displacement volumes:
If too much spacer or cement was pumped, it could overload the system. - BOP not sealed or misrouted flow:
If valves weren’t lined up properly, it might have forced flow back through the BOP stack.
Consequesces:
Cement contamination of BOP stack:
Could lead to functionality issues (sticking rams, failed seals).
Requires thorough cleaning or possible BOP teardown.
Operational delay:
Time lost cleaning cement from cellar and inspecting BOP.
Environmental hazard:
Cement in the cellar may require special cleanup.
Increased cost:
Rig NPT (Non-Productive Time), cleaning, inspection, and possible replacement of damaged equipment.
How to Prevent This in the Future:
Flow checks and proper monitoring of returns during cementing.
Clear communication between cementers and rig crew.
Pressure monitoring systems in place and watched closely.
Regular maintenance and inspection of flow lines and valves.
Verify flow paths before starting displacement.
Have contingency procedures ready for pack-off scenarios (e.g., divert lines or kill line alignment).