Offshore staff
HOUSTON – Helix Energy Solutions and SBS Energy (SBS) have set an offshore snubbing unit/hydraulic workover world record onboard the Q4000 after completing the Ozona flowline cleanout to a length of 28,789 ft (8,775 m) on Garden Banks block 515 in the US Gulf of Mexico.
In 2014, the Ozona well and flowline, located in 3,276 ft (999 m) water depth, were shut-in after becoming plugged with asphaltenes. In 2016, the well was plugged, the subsea tree was recovered, and an attempt to clean out the flowline was made using coiled tubing with tractor tooling. The coiled tubing reached a length of 23,059 ft (7,028 m) but failed to reach the full length of the flowline (28,789 ft), which was connected at both ends (A&B) with a pipeline end termination (PLET).
In August 2020, Helix recovered PLET A to the DP-3 intervention vessel Q4000 via a drillstring and rigging attached to the PLET hook and lifted through the water column. The flowline and PLET were secured on the vessel floor, and the pressure was bled off from the flowline, which was then cut away from the PLET.
Helix installed a slip-on wellhead on the flowline and rigged up surface pressure control equipment along with a 340k snubbing unit from SBS Energy. The company ran drill pipe into the flowline with the snubbing unit, the treatment fluid was heated with special equipment to +130°F (54°C) on surface and pumped down the drill pipe to dissolve asphaltenes along the flowline. It ran the drill pipe to a final measured depth of 28,789 ft while washing and reaming the flowline clean.
The flowline was then flushed and displaced to seawater for the final circulation. The drill pipe was recovered from the flowline with the snubbing unit. The surface equipment was rigged down and the flowline was capped with a blind flange.
According to Helix, the highlight of the operation was to clean out the Ozona flowline from the Q4000 rather than cutting the flowline up into sections. This reduces the number of subsea lifts, the EHS exposure, and overall timeline for the flowline abandonment.
The flowline was lowered subsea with the deployment rigging and drillstring where it was laid back in the original trench on the seafloor. This is another benefit of being able to perform the full cleanout in a single lift and requires the least amount of onshore disposal of flowline components.
To date, this is said to be the longest subsea flowline cleanout conducted via this method. The previous snubbing record depth of 23,800 ft (7,254 m) was set in 2006 by Helix (then Cal Dive) on the Q4000 during the Mariner Energy Pluto pipeline clean out.
12/09/2020
