Routine workover to change electrical submersible pump led to a well control incident and platform fire with fatality
IOGP Well Control Incident Lesson Sharing #24-8
During a routine workover consisting of changing out an electrical submersible pump, a well kicked causing a flow of oil and gas coming out of the tubing string. The well was secured, but the clean-out after the incident was performed without using dedicated equipment to safely handle the hydrocarbons. During the clean-out, a fire developed that rapidly spread to other platform areas and tragically caused a fatality.
This incident is one of many which seem to be affected by risk normalization during operations in depleted/not naturally flowing reservoirs. Well control standards are frequently lowered in these situations, with the consequence that equipment and competence are insufficient to prevent escalation of an incident.
The 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 mail to share it further within their organization.
What happened?:
- During the POOH of the completion for the replacement of the electrical submersible pump, the well kicked and a flow of oil & gas was observed coming out of the tubing string.
- Well was shut in with a kelly cock installed on tubing and with the annular preventer: no pressure build up observed. Well was filled up with water and the flow check confirmed that the well was static.
- BOP was re-opened and direct circulation was established at current depth to remove traces of hydrocarbons and ensure clean sea water (kill fluid) was present in the wellbore.
- While circulating, a deflagration occurred below rotary table and fire developed from the rig substructure to mud tanks and production platform main deck.
What Went Wrong?:
- Routine workover to change out the ESP pump on a mature depleted reservoir.
- The continuous hole fill up with sea water was not implemented while POOH the completion to reduce reservoir flooding and to not compromise future oil recovery.
- Due to the severe losses, the hole was regularly filled up with a controlled volume of water and the fluid level in wellbore was not maintained controlled at surface.
- The workover rig set up at the time of the incident provided limited options for circulation with a closed BOP. A dedicated poorboy degasser was not installed and the only available alternative to safely manage the gas would have been circulation through the platform separator. This option was more complex to manage and it was not chosen.
- No dedicated fixed gas detection system installed on workover Rig.
- Gas detection relied upon production platform sensors only. WO Rig areas were not entirely covered by platform gas detection system.
- The cleaning of crude oil traces around the workover Rig Area (from previous well release event) was not completed yet when the fire occurred causing a rapid escalation of the event.
Corrective Actions and Recommendations:
- Design of specific no damaging LCM pill to allow fluid return and conventional well monitoring, during ESP change in depleted reservoir.
- Dedicated fixed gas detection system mandatory for WO Rigs.
- The hazard posed by a limited quantity of crude oil previously spilled on the WO rig floor area was not properly evaluated. The oil removal and the rig cleaning should have been completed before resuming operation of the well.
safety alert number: 370
IOGP Well Control Incident Lesson Sharing http://safetyzone.iogp.org/
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