Apache has semi-submersible Ensco 8503 on site at Atwater Valley Block 426 doing “routine P&A work” in about 6617 feet of water, a spokeswoman confirmed.

Initial decommissioning operations were due to commence on 24 February and take 15 days to complete, according to a regulatory filing.

The Bureau of Safety & Environmental Enforcement has estimated P&A liabilities for the lease to be in the range of $5.5 million.

The Bass Lite field connects to the Eni-operated, Williams-owned Devil’s Tower spar via a two-well subsea tie-back and a 56-mile flowline.

The field was first discovered by BHP Billiton in 2001, but was deemed non-commercial. Mariner Energy later acquired the lease and proved up the discovery. It came online in 2008 and produced its last cubic foot of gas in mid-2014, US records show.

Apache acquired Bass Lite as part of its $2.7 billion merger with Mariner in 2010. That deal marked Apache’s entry into the deep-water US Gulf, but the company has since shifted its operations away from the offshore region, despite retaining considerable acreage.

Ensco 8503 is officially under a long-term contract with Stone Energy, which has been aggressively trying to farm out drilling slots for the rig.

A glutted global rig market has made that process difficult for Stone; even the secondary sublet market is oversupplied and seen as increasingly competitive with primary rig contractors.

The rig is scheduled to work for Apache from March to May of this year at a dayrate of roughly $250,000. It will then go back to Stone, which may drill either its Lamprey or Derbio prospect, assuming a partner can be found.