By Andrew Hobbs

NECESSITY is the mother of invention, and the cliché is true for staffers of the survey division of Total Marine Technology (TMT), which has designed a new device for tracking a drill string at subsea depths.

The company’s client was drilling from a semisubmersible platform in 1,200 metres of water offshore Australia, and was looking for a way to ensure the drill bit hit the exact location it wanted in order to spud its well.

TMT Survey had not originally been invited to tender for the rig positioning services project, company survey manager Adam Hamilton told Oil & Gas Australia, with the company originally contracted to provide remotely operated vehicles (ROVs) to the client.

“Typically one would have a subsea acoustic tracking transceiver on the rig, which is used to track and interrogate a beacon on the ROV,” he said.

“This rig didn’t have one, so the client needed a method to track the subsea beacon on the ROV … to localise the drill string prior to spudding.”

The solution, Mr Hamilton said, was a dynamic acoustic tracking transceiver known as the FATT Buoy – the Floating Acoustic Telemetry Transceiver.

Containing an inertial aided ultra-short baseline (USBL) system and a high precision differential global navigation satellite system (DGNSS), the FATT Buoy allows tracking of compatible beacons to depths of up to 4000 metres.

The resulting accuracy of the system combining surface positioning and subsea tracking is 0.2 per cent of the operating slant range (water depth), TMT Survey said.

The device can be used on operations needing a USBL even when a through hull moon pool is not available, or if an over the side USBL fixture is not feasible.

Once deployed, the TMT FATT Buoy can be held in place by crane wire, winch or simply tethered to a vessel or platform.

Using this method would mean the use of stereotypical survey technology such as a seabed array with long base line compatts– likely to be a costly and time consuming exercise – could be avoided, Mr Hamilton said.

“It is efficient, portable and deployable by crane or winch on the rig – and there is no need for another support vessel,” he said.

“It means this deployment method is taken off the critical path.”

The device is one of the first to be put together by TMT Survey, which was spun out of the Australian operations of SapuraKencana GeoSurvey earlier this year.

The group had previously worked mostly in Malaysia and Indonesia through SapuraKencana Australia, Mr Hamilton said, though he added that the group was currently working on another Australian project.