Chevron needed to survey 14 sites in the Gulf of Mexico, most of which were slated for decommissioning, so it hired Lockheed Martin to deploy its new Marlin AUV to assist. Chevron subsea survey engineer Olugbena Esan and Lou Dennis, Lockheed Martin business development manager, talked about the project at the Subsea Survey IRM 2012 conference.
During two weeks last July and August, Marlin surveyed 11 platforms and surrounding seafloor to a radius of 400ft. It also surveyed three partially decommissioned or operational sites, producing 3D geo-referenced models.
The first survey for Chevron was conducted 22 July and the last on 7 August. Marlin and its docking cradle and launch-and-recovery crane were loaded onto 150ft-long utility boat Lauren LaCoste in Port Fourchon, Louisiana, and hauled to the sites.
The crane lowered Marlin below the surface of the water for launch. Controllers on the vessel used acoustic communications to start Marlin on its pre-programmed mission. The link enabled real-time monitoring and a stop command if needed.
Marlin followed a predetermined survey route and used a sensor array to gather point-cloud data as it circled the targeted platforms, spiraling deeper and deeper for complete coverage. It ran 62 hours, and traveled 76 miles in waters 26ft to 125ft deep.
Marlin is rated to operate in waters as deep as 1000ft.
At the end of each survey, the AUV returned to a rendezvous point. There it used a nose-mounted, V-shaped tool to capture the recovery cable autonomously while underwater. The crane then lifted the vessel and placed it in the Marlin cradle system on the utility vessel’s deck.
In the cradle, a hard-wired connection downloaded data Marlin had gathered. Within 24 hours, Marlin software created rough, 3D pictures of what Marlin had seen. On two occasions, Chevron used the early pictures for revisits.
The data also was transmitted ashore, where teams created high-resolution, geo-referenced 3D images that were delivered to Chevron five days later. All final reports were submitted within two weeks.OE