The underside of a flushing operation

In February 2016, the AHTS Bourbon Liberty 235 conducted a flushing operation at the Odudu oil & gas field, operated by Total Nigeria. At the helm, Captain Oleksandr Kralesnikov. He tells us the story.

It was February 22, 2016. Thanks to her large deck area, the Bourbon Liberty 235, traditionally dedicated to anchor handling and towing missions, can accommodate all the equipment needed for a flushing operation. And on that day, she proved it. "From the port of Onne, where we were positioned, the vessel was loaded with 9 pieces of drain pipe, each measuring 10 m long and 30.48 cm in diameter as well as a tank of acid," says her captain.

But what is flushing? "It's an operation to clean the inner walls of pipelines, which helps to increase the oil pumping rates. In fact, over the life of a platform, elements can be deposited on the walls of the pipes, gradually reducing their effective diameter. Maintenance, by injecting acids, helps to prevent an obstruction and a gradual decline in production”.

a delicate operation

Later in the day, the vessel headed for the Odudu field, off the Nigerian coast, where personnel from Halliburtion and EMAS, which chartered the vessel, were transferred aboard from the floating storage & offloading unit (FSO). Hand in hand with the BOURBON crew, they connected the 9 pieces of pipe together one by one.
"The drain pipe was then connected to the Fi-Fi system – the Fire Fighting water pumps – to the port side jets located on the main deck in the vessel's winch zone. Lastly, one of the pipe's flanges was connected to the vessel's Fi-Fi system, and the other to the ODP-1 platform," says Oleksandr Kralesnikov.

The goal? To conduct the flushing operation using the pipeline, from the well to the FSO. "After a few hours of work, the pumping flow was still not sufficient. That's when I invited the Total engineers on board, and with them we decided to activate the second Fi-Fi pump. And that worked!"

85 hours in dp mode

Throughout the operation, the Bourbon Liberty 235 was placed in Dynamic Positioning (DP) mode, connected to the platform by the drain pipe. "Two officers were on the bridge at all times, one at the forward station to operate the DP mode, and the other at the rear helm station to handle emergencies and monitor the condition of the pipe, of the sea, and weather conditions." In all, 85 hours were spent in DP mode.

Naturally, safety procedures, drastic for any offshore operation, were scrupulously respected: "All the parties were involved in preliminary risk analysis and a safety meeting was held to explain the measures to be taken in the event of a weather incident: Fi-Fi pump shutdown, switch to rear DP mode, even the total shutdown of operations under our stop work policy."

It was an operation controlled from start to finish and which earned the captain and his crew the praise of EMAS and Total.