Planning and preparation – Key elements for prevention of MPD well control incidents
During drilling the 6" reservoir section in an unconventional well, a kick-loss situation occurred. After opening the circulation port in a drillstring sub-assembly, LCM was pumped to combat losses. When LCM subsequently returned to surface it plugged the choke. Circulation was stopped, the upper auto-Internal BOP (IBOP) was activated, and the choke manifold was lined up for flushing using a mud pump. During the course of this operation mud backflow was observed at the Shaker Box. The Stand Pipe Manifold and mud pumps were isolated to investigate. After a period of monitoring the stand pipe pressure, the upper IBOP, located at the top of the drillpipe, was opened to attempt to bullhead mud into the drillstring. Upon opening, a pressure, above 6500psi and exceeding the surface system safe working pressure, was observed. The upper IBOP was closed immediately and the surface system bled down. An attempt to close the lower manual IBOP as a second barrier was not successful. Due to the presence of high pressure, the Stand Pipe Manifold could not be used as the second barrier, nor could it be used for circulation. Well control experts were mobilised to perform hot tapping and freeze operations which were successfully executed and allowed a high-pressure drillpipe tree to be installed in order to re-instate 2 barriers on the drillpipe.
What Went Wrong?:
- With the down-hole circulation sub-assembly open in the drillstring, the upper IBOP was either leaking or remained open due to activation malfunction (this could not be substantiated), and a flow path developed up the drillpipe.
- The line up for flushing the Choke Manifold with the mud pumps did not allow for adequate well monitoring. The set up as used resulted in unexpected flow up the drillstring to go undetected.
- It was incorrectly assumed that monitored volume gains were due only to mud transfer.
- Assessment of flow, volume and pressure risks did not consider in sufficient detail the concurrent operations involving pumping mud off line and a pressurized drillstring.
- Operational focus was on choke manifold flushing whereas supervision should have maintained oversight of the broader situation including well monitoring.
Corrective Actions and Recommendations:
- Develop a barrier plan for all operational steps; always update the plan as a result of operational changes prior to continuing (ie. ensure a robust Management of Change process).
- Take the time required to verify that intended barriers are in place as per the Barrier Plan and, when activated, have operated properly (eg. IBOP’s).
- Install a landing nipple above the down hole circulation sub-assembly to allow a sealing drop dart to be run if required.
- Always close-in, or line-up, in such a way that allows for monitoring of all the closed-in pressures at all times.
- “Walk the lines” prior to commencing (concurrent) operations involving pressure and flow.
- Develop procedures in advance for flushing of the Well Control system, especially for recognisable potential cases of concurrent operations.
- Develop clear procedures covering all aspects of unconventional operations, including reasonably expected scenarios, and ensure effective communication of these to all relevant staff.
safety alert number: 260
IOGP Well Control Incident Lesson Sharing http://safetyzone.iogp.org/
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