The incident occurred on Draugen in connection with a wireline operation in a well. The well was completed and started producing in 1994. Since January 2010, the well has been shut-in. Planning for the wireline operation started in the 4th quarter of 2009. During a planned test, it was discovered that the hydraulically operated main valve in the Xmas tree was not tight, which would entail repair or replacement. The wireline operation was therefore postponed until the main valve had been fixed. At the end of November 2010, the main valve had been repaired, and the implementation of the planned wireline operation could start again.
The primary objective of the wireline operation was to replace the existing gas lift valve. To gain access to the gas lift valve, the subsurface safety valve must be extracted. When pulling the SSV, it became stuck in the valve head and blocked operation of the upper and lower main valves. The wireline toolstring was disconnected from the safety valve, completely pulled out of the well, and placed in the tool-catcher in the lubricator. The swab valve on the Xmas tree was closed.
The released toolstring blocked the W/L BOP valves, due to insufficient length of the lubricator. There was only one remaining barrier during further modification and re-building of the toolstring for subsequent run sequences.
One nonconformity was identified during this phase, and this led to preparing risk analyses for replacement and modification of the toolstring with only one barrier. The new toolstring was connected to the subsurface safety valve and put back in the subsurface safety valve’s nipple profile. Subsequently, two mechanical bridge plugs were inserted in the well above the subsurface safety valve. Other valves in the Xmas tree were closed, pressure-tested and accepted.
The plan was for the wireline operation to use toolstrings that were longer than the available length between the lubricator’s tool-catcher and shear ram on the wireline operation’s BOP control. This use of a long toolstring involves increased risk due to obstructing the use of relevant barriers in an emergency situation. In this situation the opportunities to cut the wireline were impeded, and in addition, valves in the Xmas tree were blocked. The risk contribution for the actual incident was not identified in the operator’s original wireline operation programme. It was also not identified in the revised plan after the incident involving loss of well barriers had occurred.
The incident did not result in injury to personnel, but limited material damage was registered, and major accident potential was present with one remaining barrier against hydrocarbon outflow from the well.
The direct cause of the incident was the subsurface safety valve becoming stuck in the Xmas tree. It is not uncommon for damage to valve inserts to occur when extracting equipment from the well. When equipment becomes stuck, there can be increased strain on the equipment due to tugging and pulling to free the toolstring.
It is not possible to establish fail-safe methods for preventing things from becoming stuck in the Xmas tree during wireline operations, but robust solutions, analyses and a correct understanding of the risk that may be expected, can contribute to prevent the loss of well barriers if something gets stuck.
The investigation of the incident identified the following non conformities:
1. Inadequate management. It was identified that the following items constituted deficiencies in the planning and management of the operation:
- risk factors were not sufficiently highlighted in the company’s well intervention programme
- the plan was to use a toolstring which was longer than the available lubricator length, which led to the toolstring blocking the BOP
- the toolstring obstructed access to relevant barriers during this emergency situation and the possibility of cutting the wireline in an emergency situation
- there was only one barrier available when modifying the toolstring between each run sequence after the subsurface safety valve (SSV) became stuck
- as the toolstring blocked the BOP and swab-valve in the operation phases by freeing the SSV from the Xmas tree, the only remaining barrier was the upper lubricator gasket
- in the event of an escalation of the incident with further loss of well control, a separate action plan for this well intervention had not been prepared
- the company’s assessment of the situation entailed that other wells on the facility during this emergency situation with loss of barriers were not shut down
- the company’s assessment of the situation entailed that there was no need for an internal investigation
2. Inadequate risk assessment. It was identified that:
- the need for sufficient height when rigging the lubricator in the area was not emphasised
- the outcome with this type of SSV becoming stuck in the Xmas tree was not identified in the risk review before the activity
- consequence-reducing measures were not implemented on the facility when the SSV became stuck in the Xmas tree
- loss of barriers was not sufficiently emphasised in the risk reviews that were carried out in connection with the well interventions
3. Inadequate well barriers. It was identified that the well barriers in three out of nine different phases of the operation were not sufficiently qualified.
- when the SSV was stuck in the Xmas tree and connected to the toolstring, the barrier situation was deficient
- when down rigging the wireline operation equipment with the toolstring after disconnecting the stuck SSV, the barrier situation was deficient
- When carrying out wireline operations to free the SSV form the Xmas tree, the barrier situation was deficient
4. Inadequate well barrier drawings. During review of documents relating to the wireline operations it was identified that:
- well barrier drawings in the work description had not been prepared for the different phases of the wireline operations
- the well barrier drawing that was used, only described a production well under normal conditions
5. Inadequate well control. It was identified that:
- the well was a discharge source with a shut-in pressure of 22 bar
- in the event of loss of well control the facility does not have a derrick for re-establishing well barriers
- in the event of an escalation of this incident, the facility lacks other immediate intervention opportunities
- the drilling fluid system on the facility was not used for well control at the time of the incident
- the cement pump unit on the facility was not staffed at the time of the incident
- the maintenance status of the cement pump unit was not known to the executing personnel
6. Inadequate daily reporting of drilling and well activities. During review of DDRS it was verified that:
- data has not been reported from this well in connection with well intervention
The investigation report also included a series of observations related to the incident which can be summarized below:
- There is a need to improve the personnel safety when rigging and executing wireline operations.
- Internal requirement for conducting regulations courses for personnel were not complied with.
- The company’s system for making governing documents available on the facility could be improved.
- The company’s acceptance criteria for putting the subsurface safety valve back in the valve profile in the well in this emergency situation can be improved.
- There was a need to improve the company’s assessment regarding use of the cutting function of the main valve and use of temporary shear ram.
- There was a need to improve the company’s use of the safety device when hanging the toolstring.
Source: Norwegian PSA