Well stimulation: AHTS where you don't expect them

AHTS vessels are of course generally known for their role involving towing and anchor handling operations for oil platforms. The abilities of these vessels are also very useful for wellhead maintenance operations and well stimulation operations that are carried out from the surface only.

Gabon – ANE platform, Anguille site off the coast of Port-Gentil, February 2015

ANE is a shallow-water platform located 15 km off the coast of Gabon, positioned directly on the seabed at a depth of 30 m. This platform has 6 wellheads in service, and 10 technicians work there. Maintenance operations are necessary to optimize platform productivity. This is why the crew of the Bourbon Liberty 223 was called on by Total E&P Gabon to carry out flushing operations. The Client also assigned a Schlumberger team specialized in this type of operation, in order to ensure a successful mission: carrying out injection tests on the platform’s wellheads.

During the lifespan of a platform, substances are deposited on the inner surface of the lines leading up from the reservoirs, gradually reducing the diameter of the lines, which causes the flow rate to decrease. Maintenance operations on these lines, also known as pipes, involve injecting acid mixtures in order to prevent obstruction and the progressive deterioration of production. In addition, the pressure of the injection can sometimes give a boost to the flow rate from the reservoirs; this process is known as well stimulation.

This operation was another addition to the growing list of achievements for this Bourbon Liberty 200 AHTS that has gone above and beyond its traditional roles involving anchor handling, towing and package transportation. "This type of operation demonstrates the versatility of our crews as well as our AHTS vessels. BOURBON is a genuine 'solutions provider' thanks to the skills of our employees and the reliability of our fleet." explains Captain Adrien Richaud.

Using dynamic positioning, the vessel was connected to the platform by an umbilical cable through which products can be passed at very high pressures (up to 200 bars). The pumping station and all necessary equipment to ensure the success of each step of the mission was located on the AHTS Bourbon Liberty 223:

• Verification of system tightness and pressure test for each wellhead
• Cleaning pipes and well stimulation by injecting acid
• Verification of injection flow rate variations for each well

The operation lasted 10 days, during which the teams took turns night and day, without any dead time, in order to test the 6 wellheads. The Captain and First Mate, responsible for safety on board, coordinated the operations with the crews located on the platform. The vessel crew, consisting of 14 members, provided the necessary support to the Schlumberger teams, in close contact with the bridge.

Our goal: to not waste any of the client’s time during anchor handling operations. The versatility of the Bourbon Liberty 200 made it possible to easily adapt to the stimulation operations so that the client was not obliged to use a specialized vessel on a systematic basis.

Client Satisfaction

Pierre Allain, Reservoir engineer for Total Gabon, explains:

"Thanks to dynamic positioning and the available space on the deck, we were able to carry out injectivity and acidification test operations on 6 wellheads without any weather standbys and without needing to return to the base to refill the vessel with acid."