• Published: 4 Feb 2014
  • Incident ID: 3493

Gas Release from Hydraulic Oil Annulus Returns Tank

Cause & Consequence

  • Uncontrolled release of a flammable gas or liquid
Incident Consequence
Hydrocarbon release

Incident Location

Fixed Installation

Incident Activity

Production operations

Specific Incident Equipment

Hydraulic Annulus Oil Returns Tank and the hydraulic well annulus controlling the SSSV

Lessons Identified

  • Historic managements of change processes had not taken into account the possibility of gas returns to the hydraulic oil annulus returns tank through seal leakage or gas entrained into the hydraulic fluid.
  • The level of independent checks on well operations team procedures and processes (by the production team) were found to be inadequate

Incident Recommendations

A number of actions resulted from this incident including engineering controls to physically isolate production (including the annulus returns tank) during well operations. The wells team going forward will handle any hydraulic oil and gas returns post SSSV removal through separate PCE (Pressure Control Equipment) equipment isolated from the installations return lines and annulus returns tank. Other actions include:

• Well operations manual to be updated to define the method required for bleeding the SSSV control line and/or hydraulic control annulus to ensure the following:

a) Sufficient barriers are defined, available and maintained throughout the operation.

b) The barriers are independently checked and approved prior to pulling the SSSV by someone delegated with sufficient seniority and knowledge of the asset.

• Future Well Operation work packs are to be developed and include:

a) Detailed method statement and drawings specific to the well and hydraulic controls arrangements present, and a full risk assessment that ensures well control barrier philosophy is met.

b) Risk assessment to be undertaken with cross functional review and approval

c) Draft Work Control Certificates to be developed and included with sufficient detail to enable more effective tool box talk

d) All future well operations will be managed using a dedicated Well Intervention Permit

•Undertake suitable modelling to ensure that all annulus controlled wells do not have the ability to overpressure their respective return tanks

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