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Esso Petroleum (ExxonMobil)

ExxonMobil Blackback Phase 1 Development Project: Placement of Subsea Flowline Jumpers, Bass Strait Australia

ICON Engineering was awarded the contract by ExxonMobil to place the flowline jumpers on the seabed in designated locations such that they could be tied in later by ROV.

The project was unique in that the flowline placement was undertaken from a semisub drilling rig. Traditionally, this work has been carried out from a DP Diving Support Vessel. The method was cost effective since the rig was on site to drill the wells.

Rig and support vessel for the Blackback project

The Sedco 702 drill rig and support vessel on station during the Blackback installation

The Blackback project consists of three subsea wells interconnected with flexible flowlines in a daisy chain configuration and tied back by subsea pipeline to an existing offshore platform. The water depth at Blackback is approximately 420 metres.

The project was unique in that the flowline placement was undertaken from the semi-submersible drilling rig Sedco 702. Traditionally, this work has been carried out from a dynamically positioned Diving Support Vessel. The method is cost effective since the rig is on site to drill the wells.

The flowline jumpers were loaded into ICON designed deployment frames for transport offshore. Prior to departure, the deployment methods were fully tested onshore and the flowlines hydrotested.

deploying the blackback frame.jpg
Deploying the Blackback subsea frames

 

Offshore, each frame was lifted from the supply boat by the rig crane and lowered into the water. The frames were then passed over to the work wire of a second anchor handling vessel and lowered to the seabed.

frame lifted off vessel.JPG

The frame being lifted off the vessel

 

After placement of the frames on the seabed, they were then lifted and oriented into the final position by the drilling rig using a stab in tool on the drill string. The jumpers were released by ROV and frames removed.

The work was completed without a hitch. The frames were deployed to the seabed in less than 12 hours while the rig was drilling. Final positioning and orientation using the ICON designed stabbing and orienting string was also completed with no problems using less than 12 hours rig time.

Support for Diverless Flowline Connection System (DFCS) ROV Activities

An additional part of the work scope included the design and installation of significant modifications to the Sedco 702 to handle the large Diverless Flowline Connection System ROV that was used for the final flowline tie-in.

A large cantilevered ROV launch platform was installed on the port side of the rig. This allowed the ROV to be launched clear of the rigs pontoons.

In addition, a subsea deployment system was devised using a winch and the rig's crane to lower umbilicals and tie-in equipment weighing up to 15 tonnes to the seabed. This required further deck extensions and considerable procedural engineering to allow the operation to be carried out safely.

The preparatory work was carried out under difficult conditions at the end of another operator's drilling program and during the tow to site. All work activities were completed on schedule and without incurring downtime, allowing the rig to commence the project activities immediately on arrival.

Lowering the ROV during the Blackback installation

Lowering the ROV during the Blackback flowline installation
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