Centrica - Chestnut scale squeeze journey

By collaborating with the service community and adopting a ‘One Team’ approach novel solutions to challenges were identified and successful projects delivered at a significantly reduced cost.

Overall a cost saving of 79% was realised. These savings were subsequently used to fund other projects across different areas of the business. Production from one of the well assets increased by 25% helping to extend the life of that asset offsetting the low commodity price.

Had an industry standard approach been adopted, projected costs would have resulted in the activities being sub-economic in the low commodity environment.

As well as allowing us to source new ways of working the ‘One Team’ approach has helped to break down recent barriers along the supply chain and created a spirit of greater collaboration with and between our vendors emphasising that if we all work together we can all benefit.

Description of Best Practice

As a result of irregular sampling and delayed sample analysis on a CNNS oil asset, Barium Sulphate scale started to form in one of the subsea wells tied back to an FPSO.

Flow monitoring in the comingled flow system eventually identified a problem with the wells flow performance. Discrete flow testing and sampling confirmed 90% loss in a single wells production as a result of scale formation in the wellbore.

Initial opinion was that a drilling unit or intervention vessel would be required to re-enter the subsea well and mechanically remove scale returning the well to production. This was the industry standard method of addressing the problem.

Focused on delivering value in a low commodity price environment, Centrica presented the scale removal challenge to a team of internal engineers and external experts from the service community. A series of open forums were held to identify all potential solutions. After a peer review of options identified, chemical removal via the FPSO was sanctioned as the preferred option for execution.

A number of challenges had been identified with the preferred solution:

Deck space on the FPSO
Volume of chemical required
Placement of chemical in the wellbore
Materials compatibility
Effectiveness of the chemical treatment
Conflicting priorities on the FPSO
Weather limitations in the time period identified for execution

A ‘One Team’ approach was adopted and key accountable people from the Centrica project team, FPSO owner, field Operator, chemical vendor, pumping vendor and marine vendor were identified. The team was tasked with ensuring the project received the priority required for returning the well to production without impacting existing safety critical activities planned during the same period.

On schedule a PSV (production support vessel) modified as a chemical heating and pumping vessel sailed to the FPSO location and deployed heated scale dissolving chemical to the wellbore via the FPSO through the existing subsea flow system. After a period of back production and well clean-up, managed by the field Operator, the PSV pumped scale protection chemicals to the wellbore returning the well to production. Subsequent flow testing confirmed not only a return to pre scale production rates but an increase in the PI (productivity index) of the well and a production increase of approximately 24% over original rates.

The lessons taken from the successful PSV scale dissolver and treatment operation were further applied when a second well was identified as requiring a scale protection chemical treatment. Unlike previous treatments where chemical was injected with support from a DSV, the same ‘One Team’ approach identified a different method of chemical deployment to the wellbore via the FPSO through existing subsea pipework.

The new method was planned mobilized and executed in a shorter timeframe to the DSV method and delivered at a 79% cost reduction over the previous solution.

Contact: Alan Quirke, Centrica E&P