Woods Hole Group has a long history of designing, installing and operating environmental measurement systems on a range of platforms from fixed production platforms and FPSOs on the continental shelf to semi-submersibles and drillships in deep water.  That tradition continued this year with the award of contracts for ADCP systems on four new-build drillships in the Gulf of Mexico.

The first award was from Chevron for design, fabrication, installation and commissioning of ADCP deployment systems on the Transocean Discoverer Clear Leader (DCL) and the Discoverer Inspiration (DIN).  Chevron has a long term charter of these drillships and intends to operate them in the deep waters of the Gulf of Mexico.  

These deployment systems are improved versions of the unique moonpool deployment system developed by Woods Hole Group in 2000 for the Transocean Discoverer Spirit, which is still in operation today.   The system is based on a two rail (I-beams) track attached to the side of the moonpool.  The ADCP is mounted in a carriage, which rides a sled along the rails to its deployed position at the base of the moonpool.  The advantages of the system over the more conventional ‘over the side’ deployment system include more accurate data and less frequent service visits.  Also, the moonpool deployment system allows the ADCP to remain in place and collect high-quality data during severe storms, when an over-the-side system would have to be removed from the water to avoid damage. 

The DCL system was installed and commissioned in July 2009 and the DIN system is scheduled for installation in early 2010.

The second award was from BP America for design, fabrication, installation, commissioning, monitoring and servicing ADCP systems on the first two of Pride International’s sixth generation, ultra deepwater drillships under construction in South Korea - the Deep Ocean Ascension and the Deep Ocean Clarion.  The Deep Ocean Ascension is due into the Gulf of Mexico in June 2010 and will be joined by the Deep Ocean Clarion in December 2010.

The identical measurement systems involve a downward-profiling TRDI 38kHz Ocean Observer ADCP and a TRDI upward-looking 300kHz Workhorse ADCP.   Together these sensors will obtain current data from the near surface to about 1000m below the sea surface.  The ADCPs will be mounted on a spreader bar suspended over the side using a dual-cable gantry mechanism mounted on a platform projecting outward from an upper deck on the drillship.  The current profile data will be transmitted in near real time to the National Data Buoy Center in accordance with the requirements of MMS NTL No. 2009-G02 as well as to WHG for system performance monitoring.

These systems will be among the first in the Gulf of Mexico to utilize Teledyne-RDI’s underwater electronics housing for the 38kHz Ocean Observer.  This will permit the use of electromechanical support cables, rather than separate suspension and electrical cables, providing increased reliability and ease of deployment.

The current profiles collected with all of these ADCP systems will be used for operational purposes and to fulfill the Minerals Management Service requirement to report in real time current profiles from drilling and production platforms operating in water depths greater than 1000m.  For offshore energy exploration and production, real-time deep water current data guides effective and safe drilling operations.  Beneath the surface of the ocean, discrete masses of water move at different speeds at different depths. These strong currents can present hazards to drilling operations, especially as drilling moves into increasingly deeper water. The forces on risers can increase dramatically due to currents associated with the Loop Current and its eddies in the Gulf of Mexico.

Current data can also be used to develop defensible engineering parameters for the design of offshore facilities.  Both real-time and historical oceanographic and meteorological data are critical components of daily drilling operations and long-term planning.

David Szabo, M.S.
Houston Office Manager

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