Courtesy of akofsoffshore.com

At the end of last year, Petrobras deployed its first wet Christmas tree using cables in the pre-salt area.

The main change involved was the use of a subsea equipment support vessel (SESV) to install the equipment rather than a traditional drillship. This resulted in a time saving of approximately 10 days, generating a gain of more than $5 million.

The well on which the Christmas tree was installed using this technique, called 7-SPH-2D-SP, is located in Sapinhoá field, in the pre-salt layer of the Santos basin, at a depth of 2,130 m.

The operation, which involved lowering the Christmas tree into position and installing it on the wellhead using a suspended cable, was carried out from an SESV using a subsea equipment guidance system.

This installation technique replaces the use of drillships, which are much more expensive to charter. SESVs have some other major advantages in relation to drillships. For example, using a drillship it takes around 10 hours to lower a riser 1,000 m in the open sea. Consequently, the time taken to lower a Christmas tree for installation on a well at a water depth of 2,300 m is 40 hours on average. SESVs, on the other hand, can perform the same maneuver in less than four hours, due to the cable launch and return speed.

Petrobras had already used this technology at depths of up to 2,000 m. Following engineering studies, some adaptations were made to the SESV Skandi Santos, enabling the vessel to install equipment at depths of up to 2,300 m.

After the success of this first experience, the use of SESVs has now been proven as a viable option for the pre-salt layer, and this will help reduce operating costs and times. Petrobras has now chartered a second SESV, which is being adapted for depths of up to 2,500 m and which should start operating in the second half of 2016.

Source: worldoil.com