Belanak betokens gas breakthrough
  from: Offshore Engineer
  by: John Mueller
  Saturday, November 01, 2003

The development of South China Sea gas resources to supply the burgeoning international markets of Southeast Asia took a significant step forward with the completion of the Belanak FPSO hull. John Mueller reports.

The Belanak FPSO will be equipped with one of the most complex processing systems ever installed offshore. The vessel will process gas, oil, and condensate produced from multiple fields in the eastern portion of the ConocoPhillipsoperated South Natuna Sea Block B production sharing contract (PSC).

Also incorporating a plant to extract liquefied petroleum gas (LPG), propane and butane from the produced gas, the Belanak FPSO will be the first offshore LPG facility on a floating vessel in the Asia Pacific region. The FPSO is expected to have an output of 7800 standard barrels per day of butane (C4) and 14,700 standard barrels per day of propane (C3), for transfer to an LPG floating storage and offloading vessel, and will also be the central processing hub in Block B.

ConocoPhillips contracted PT Brown & Root Indonesia and Dresser Kellogg Energy Services (DKES) to design, engineer, procure, construct and install the FPSO, moorings and flexible risers. All project management services and engineering are executed from Singapore and Indonesia. Initial hull design and engineering were performed in Leatherhead, UK, and topsides engineering and procurement from Singapore. Fabrication of the topsides was subcontracted to PT McDermott Indonesia.

DKES, a Halliburton subsidiary, subcontracted construction of the hull and related electrical systems, module housing and living quarters to Dalian New Shipbuilding Heavy Industry. The shipyard, located in Dalian on the north coast of Bohai Bay, the Peoples Republic of China, started hull construction in March 2002 and completed it in 18 months.

The Belanak FPSO hull is the first of such size and complexity to be fabricated in China. The project is also the first of its type undertaken by either ConocoPhillips or Halliburton in that country.

Challenges faced by the marine design and engineering teams primarily related to the 30-year service life, heavy topsides loads with regard to stability and the need for stringent motion restriction to ensure the efficient operation of onboard LPG processing facilities.

To meet the supply obligations of gas sales agreements with SembCorp Gas (SembGas), of Singapore, and Petronas and to develop and produce extensive oil reserves in South Natuna Sea Block B, ConocoPhillips, operator, and its partners, Inpex Natuna of Japan, and Texaco South Natuna Sea Inc are developing several South Natuna Sea fields.

The cornerstone of this effort is the Belanak Field Development Project, which consists of the FPSO, two wellhead platforms, an LPG FSO vessel, gas export pipeline, oil offloading buoy and various intra field pipelines. Development cost is put at $1.6 billion.

Natuna Sea gas
In 1999 Pertamina, on behalf of the Indonesian government, signed a gas sales agreement (GSA) with SembGas for the delivery of 2.5tcf of gas over 22 years at a rate of 325 million scf/d, with first deliveries beginning in 2001. This gas is supplied from three PSCs in the West Natuna Sea, including the South Natuna Sea Block B PSC, the Kakap PSC, operated by ConocoPhillips Kakap, and the Block A PSC, operated by Premier Oil Natuna Sea.

These gas reserves are connected to the Singapore market via the ConocoPhillips operated West Natuna Transportation System (WNTS), a 656km 28in pipeline and gathering grid in the West Natuna Sea.

To further expand the supply of gas to international markets, Pertamina signed a second GSA in 2001 for the delivery of 1.5tcf of gas over 20 years at 250mmcfd from the South Natuna Sea Block B fields, starting in 2002.

This gas is transported to Malaysia via a 96km, 18in pipeline from Block B to the Duyong Complex, offshore Malaysia, for onward transport to Peninsular Malaysia.

Assembly
The Belanak FPSO hull was constructed ultilising block assembly. The aft section, representing about 40% of the hull, was built on a slipway and then launched into the sea for tow to a 375m x 80m drydock, where the fore section blocks were assembled and the hull joined.

In parallel with hull assembly, the 470t marine electrical module building was constructed on the quayside along with the 1220t, 120-person living quarters.

The hull was designed and built as a double side, single bottom configuration with no self propulsion and to the following specifications: 58m beam, 285m length, 26m depth, 255,000t maximum displacement and 18m loadline and 13.9m to 16.7m operating drafts.

The hull has a 30-year design life without the need for dry-docking, and all mechanical equipment is specified to last over this period with only routine maintenance offshore.

The entire hull is coated with high-grade paint systems, including cargo and slop tanks, over 600,000m2 of paint having been applied. Splash zones, decks and areas where mechanical damage may be expected are all coated with glass flake epoxies.

The large deck space of the Belanak FPSO can accommodate more than 13 topside modules.

The size and complexity of the topsides and the inherent difficulties involved in installing an LPG plant on a floating structure challenged both the topsides and marine designers.

The topsides, whose operating weight is nearly 31,000t, will perform a variety of processing tasks and fulfill exacting operational requirements.

Mooring, motions & risers
As the weather conditions in the Natuna Sea are favourable to a spread moored system, no turret is required.

The Belanak FPSO will be positioned with the aft end facing the prevailing northeasterly winds, secured by 14 mooring lines requiring over 11,000m of 127mm thick steel chain, each line anchored to the seabed by suction piles. The system has been shown to have a fatigue life of over 300 years and withstand a 100-year storm.

The mooring setup ensures the motion of the vessel is sufficiently stable for reliable LPG production. The allowable movement at the top of the LPG fractionation columns, some of which will be over 60m high, is about 2° from vertical, roll or pitch, including static tilt. According to DKES, the design has demonstrated less than 1.75° of deviation more than 99% of the time.

There are two riser porches located forward and midships on the starboard side, supporting nine flexible risers, comprising two production, two oil offloading, two LPG export, two well head platform gas injection and one gas export. Additionally, three 13.8kV subsea power cables exit from the riser porches.

At Batam Island, Indonesia, after a three week tow, the hull has been berthed at a new quayside, specifically built by PT McDermott Indonesia. The berth was designed to accommodate the Belanak hull during the integration of 25,000t of process topsides (OE June 2003).

The completed FPSO is expected to be towed to its installation site in the Belanak field, approximately 200km northeast of Singapore, in September 2004, with first production anticipated before the end of 2004. OE