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Oil flows from Caesar Tonga

06th August 2012

Life is returning to the oil fields of the Gulf of Mexico as witnessed by the recent first oil from Caesar Tonga

The Caesar Tonga field is estimated to hold a resource base of 200 to 400 million barrels of oil equivalent (BOE).

Located in the Gulf of Mexico approximately 300km from New Orleans in Louisiana, lies the Caesar Tonga oil field. It is situated at a water depth of about 1,500m in blocks 683, 726, 727 and 770 of the Green Canyon area of the US Gulf of Mexico (GoM).

Anadarko Petroleum is the operator of the Caesar Tonga joint development and has a working interest of 33.75 per cent in the development. Statoil, Shell Offshore and Chevron USA are the co-owners of the project with working interests of 23.55 per cent, 22.45 per cent and 20.25 per cent respectively.

High quality oil production from the field began in March 2012. The first oil was originally scheduled for mid-2011, but was delayed due to a mechanical fault in the production riser system.

The field is estimated to hold a resource base of 200 to 400 million barrels of oil equivalent (BOE). Production from the first three production wells is expected to ramp up to about 45,000 BOE a day. The field will be developed as a sub-sea tieback to the Anadarko-operated floating production platform, Constitution. The development works began in early 2007 under a combined single development that comprises Tonga, Tonga West and Caesar fields.

The first phase of development of Caesar Tonga is estimated to cost USD1.3bn and includes construction of four wells. The first three wells were put into operation in March 2012. The fourth development well is anticipated to be completed before the end of 2012.

Flow and reservoir tests on the first three development wells were undertaken during the second quarter of 2011. The wells tested flow rates of about 15,000 barrels of oil each day (BOPD) of high quality oil.

“Caesar-Tonga came on production in early March, 2012 and is currently producing at very strong rates of about 50,000 barrels of oil and 50 million cubic feet of natural gas per day from three wells,” Byron McDonald, general manager, Gulf of Mexico Development, Andarko, says. “The primary challenge for the Caesar-Tonga development was to design a subsea system that could operate at the producing pressures expected from the reservoir.

Flowlines, risers, manifolds, trees and multi-phase flowmeters were specified for this purpose. The riser system required an innovative solution, not previously used in the Gulf of Mexico – a steel lazy wave riser design – only the second application of this technology in the world.”

The topside facilities of the Constitution spar platform were commissioned in the first quarter of 2012. The offshore pipeline from Caesar Tonga was attached to the spar using lazy-wave steel catenary riser (SCR) technology, which is first of its kind to be used in the Gulf of Mexico.

“The steel lazy wave riser is not a true SCR; it’s an adaptation of the SCR theme,” McDonald says. “There is an arch built into the riser configuration that improves the fatigue performance. Our partnership installed 160 discrete buoyancy modules on the riser to create this arch. The riser departs the spar at a slight angle from the vertical and gradually curves across and up to form the arch. The riser shape then takes a downward bend until the touchdown on the seafloor.

“The Caesar-Tonga fields are of Miocene age, located below the salt. Caesar-Tonga wells drill through as much as 15,000 feet of salt before reaching the productive reservoir.”

Manufactured by Technip at its Pori yard in Finland, the spar now facilitates oil production from the Caesar Tonga field in addition to the Ticonderoga and Constitution fields.

In March Anadarko announced first production at the Caesar/Tonga development in the Green Canyon area of the deepwater Gulf of Mexico. A fourth development well is expected to be drilled and completed later this year, as part of the planned Phase I development.

McDonald is convinced that the now well-established tie-back strategy will prove beneficial for many marginal fields in the future. “Tying back subsea wells to existing platforms is reflective of our operating philosophy in the Gulf of Mexico and in other deepwater basins,” McDonald adds. “By utilising this hub-and-spoke approach, we’re able to significantly reduce the cost of developing new deepwater discoveries. In the case of Caesar-Tonga, we saved almost USD 1 billion and reduced the time it would’ve taken to achieve first production by almost two years. Anadarko utilised its 100 per cent owned Constitution spar, which had been producing since 2006, and extended its life by tying it to Caesar-Tonga.

“Our company has utilised a deepwater hub-and-spoke strategy for more than a decade, and it is a cornerstone of our Gulf of Mexico operations. We make an initial investment in a host facility and produce those discovered resources as the base project. Future discoveries can then be tied back to the existing infrastructure and significantly improving the economic threshold for subsea developments by eliminating the need for a new host facility.”

As for the future of the field, McDonald sees a bright and long future for the region. “Our current estimated resource potential is 200 – 400 million BOE.

As we gather data from Caesar-Tonga’s existing wells, there will be infill opportunities and opportunities for additional wells to keep a production plateau for a longer period of time,” he says. “This year we’re focused on achieving and even exceeding our 45,000 BOE/d goal from the first three wells and preparing to drill and complete a fourth well as a part of our Phase 1 development.”

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