The Horn Mountain development is located in 5,400ft of water, approximately 100 miles southeast of New Orleans, in the Gulf of Mexico. The deep water field lies in Mississippi canyon blocks 126 and 127. Horn Mountain is operated by BP (through its takeover of Vastar) with a 67% share. Occidental has the remaining 33% equity. The leases for the Horn Mountain field were acquired in 1997 and 1998. Exploration drilling began in July 1999 and the discovery was announced in August of the same year, when the semi-submersible drilling rig Ocean Victory drilled to 14,600ft and encountered nearly 300ft of pay from four Miocene intervals. A side-track revealed a column of around 550ft.
Delineation drilling began immediately, taking advantage of rig availability and advanced field planning. The decision to immediately appraise the field cut months, if not years, off the total development time. Eight production wells and two injection wells were drilled in 2001 using the Ocean Victory. The wells averaged 16 days per every 10,000ft drilled. The project went from discovery to production in just under 40 months.
At the point of the field coming into production, it flowed at an average rate of 15,000 barrels of oil and 12 million cubic feet of gas per day. This eventually peaked at a rate in excess of 65,000 barrels of oil and 68 million cubic feet of gas per day in 2003. The production facility can accommodate additional incremental production if new discoveries are made in the region.
Horn Mountain has been developed using a truss spar, making this the deepest free-floating dry tree system in the world. It is the second BP-operated floating production facility in the Gulf. The truss spar design that the field uses is only the third of its type in the industry.
The hull structure measures 585ft in length and 106ft in diameter. It features heave plates to dampen the movement. The hull was designed by CSO Aker and built at the Mantyluoto Works yard. Meanwhile the topsides began construction at Ingleside, Texas by Gulf Marine Fabricators. The topsides design was carried out by Alliance Engineering. The design was strongly influenced by the ability of Heerema’s Balder installation vessel, which has a maximum lifting capability of 4,700t.
Intec Engineering was contracted for the pipeline infrastructure. The lines were laid by Allseas’ vessel Solitaire. To carry out drilling operations, the rig facilities on the vessel were supplied by Helmerich and Payne.
The spar is capable of supporting 14 dry trees. The wells connect to the spar by means of a dual barrier riser system. This consists of a 9 5/8 internal riser set into a 12¾ outer riser. This was designed by ABB Vetco Gray. The large tensions from the deep waters are supported by 240ft-long by 12ft-diameter air cans.
The completed spar hull sailed from Finland in April 2002 and arrived in the Gulf in late May. The topsides production facility and quarters packages sailed from Ingleside in early June. The spar hull and topsides facilities were mated in June.
Oil is exported through Shell’s Odyssey pipeline system. Gas is transported throughout the 10in line to the Destin system operated by BP. The $600 million project is expected to result in ultimate recovery of an estimated 150 million barrels of oil and gas equivalent.
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