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Total installs first subsea gas/liquid separation in 800 meters of water in Angolan deep offshore for heavy oil

Begun in December 2007, development of the Pazflor oil field 150 kilometers (93 miles) offshore Angola is one of the biggest projects currently operated by Total. A number of technological challenges—including subsea gas/liquid separation, a first—are being met to bring the field on stream.

Ssu
Pazflor SSU. Click to enlarge.

On 30 January 2011, the Acergy Polaris finished installing three subsea separation units (SSU) for the Pazflor project, in 800 meters (2,625 feet) of water in Block 17 offshore Angola. The flagship innovation of the project, these units constitute a world first in terms of technology, according to Total.

Pazflor is the first project to deploy a development plan based on gas/liquid separation at the mudline spanning several reservoirs. Total says that this technological innovation will make it possible to meet the challenge of producing the heavy, viscous oil contained in three of the four reservoirs in this gigantic development in the Angolan deep offshore.

The Pazflor oil field comprises four reservoirs. One of them, Acacia, was formed around 25 million years ago in the Oligocene and contains light oil. The other three—Perpetua, Zinia and Hortensia—are younger, dating from the Miocene, just five to seven million years ago. They contain more problematic oil that is heavier and much more viscous. Subsea gas/liquid separation is the key to the economics of producing these challenging reservoirs.

The subsea production system for Pazflor’s three Miocene reservoirs includes three subsea separation units. Each one consists of four retrievable packages: a gas-liquid separator; two hybrid pumps to boost the liquids; and a manifold to distribute the effluents to the separator and pumps. Purpose-designed for Pazflor, the hybrid pumps are another first. They combine multiphase stages, compatible with the presence of gas in the liquid, and a centrifugal stage, to improve efficiency.

Fabrication of the SSUs, completed in 2010, entailed nearly 350,000 man-hours of work.

Both systems—the standard production loop for light oil and the new subsea separation technology—will be connected to a single Floating Production, Storage and Offloading (FPSO) vessel.

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