Case Study: Shell Nelson

The coalescer on the Nelson platform was suffering from instrumentation issues making the level determination within the vessel extremely inaccurate thus severely limiting performance. This was attributed to a build up of sludge and sand within the vessel.

After numerous failed attempts with other companies and chemical compositions, Shell took the decision to ask Denholm MacNamee to carry out a boil out decontamination of the vessel with the objective of restoring the vessel instrumentation to its proper operating levels. The vessel was not due to be opened after treatment and success was to be judged on improved telemetry.


A boil out decontamination procedure was implemented using an aqueous ZymeFlow® UN657 solution. ZymeFlow® UN657 is an aqueous formulation, a very low hazard product, and has all necessary CEFAS certification for use offshore in the North Sea.

The boil out was completed over an 18 hour processing duration including the heating of 70m³ of water. On completion, the vessel contents were drained into holding skips for settlement and disposal of residual solids.


Based on previous attempts to de-sludge the vessel, operations personnel anticipated that approximately 4–5 tons of debris would be removed. In reality, approximately 17 tons of debris was removed from the coalescer.

Client personnel were astounded by this performance. They had provisionally planned to implement a second boil out procedure to try and ensure the required result but it was evident that this would not be required and on reinstatement of the coalescer to service the telemetry performance was fully restored.


The client was very impressed by the success of the project and is now looking closely at other vessels and processes where this technology may be applied.