Devils Tower Gas Field, Gulf of Mexico, USA

Devils Tower field is located about 140 miles south east of New Orleans, at the Mississippi Canyon (MC) Block 773 in 5,610ft of water in the Gulf of Mexico. The field was originally operated by Dominion, which held a 75% working interest.

Pioneer holds the remaining 25% interest. In 2007, Dominion sold its interests in the Gulf of Mexico to Eni for $4.75bn. Eni now holds a 75% interest in Devils Tower and is the operater.

The development of the Devils Tower field was formally sanctioned in June 2001. The field began its production in May 2004 at the MC 773 A-1 well. It was the first of the eight wells that began production in 2005.

Drilling of Devils Tower

The discovery of the Devils Tower field was announced in February 2000, with the drilling of the MC 773 no 2 well.

In June 2000, well no 3 was drilled using the semisubmersible Homer Ferrington in 5,610ft of water. The well encountered hydrocarbons in three zones in a separate fault block north east of the discovery well.

Two development wells were then completed with the MC 773 no 4 well, penetrating approximately 350ft of net pay in five sands within a previously untested fault block.

The MC 773 no 5 and no 5 sidetrack extended the hydrocarbon column in six previously penetrated sands and contained over 400ft of net pay. Both wells were temporarily abandoned and completed as producers.

The field reserves are in the range of 80-150 million barrels of oil equivalent.

Spar facility

The Devils Tower field was developed using a spar with slots for eight dry-tree wells and the flexibility to accommodate future subsea tie-backs. In 5,610ft of water, this spar is the world's deepest dry-tree platform. It also uses a 94ft-diameter truss configuration and has the flexibility to accommodate future subsea tiebacks. The spar facility is owned by Williams.

The hydrocarbons produced from Devils Tower wells flow through the spar. It can handle 60,000 barrels of oil and 110 million cubic feet of gas a day. Three subsea wells in the adjacent Triton and Goldfinger platforms in blocks 771, 772 and 778 are tied back to the Devils Tower floating production. The three subsea wells, located six miles away from the spar, were connected via flowlines of 6x10in.

Though the tie back was completed in less than four days, production from the subsea wells was delayed due to Hurricane Katrina in August 2005, which damaged the infrastructure. Production began in December that year.

Contractors

The J Ray McDermott affiliate SparTEC was the general contractor and overall project manager for the design engineering, procurement, fabrication, installation and commissioning of the facility. Detailed engineering of the hull-mooring and topsides was completed in Houston, Texas.

The hull was fabricated at the company's Batam Island facility in Indonesia, while the topsides were prefabricated in Mexico at the company's TNG shipyard, then assembled and outfitted at McDermott's Harbor Island fabrication yard, based near Corpus Christi, Texas. Work at Harbor Island was completed under a strategic alliance with Bay Limited.

McDermott's Mentor Subsea Technology Services subsidiary designed and procured risers, while the company's marine division has been mandated responsibility for offshore installation, hook-up and commissioning. The contract work was concluded in the fourth quarter of 2003.

Eni's interests in the Gulf of Mexico

Eni's acquisition of Dominion's interests in the Gulf of Mexico increased the latter's reserves by 222mboe. In addition to Devils Tower, Eni has acquired Rigel / 17 Hands, Independence Hub, Thunder Hawk, Front Runner and Neptune.