A ‘float over and ballast down’ technique has been used to install a new offshore production platform at the Yakin oil and gas field, eight kilometers off the coast of Balikpapan in Indonesia’s East Kalimantan.
According to leading consulting firm, Sinclair Knight Merz, the use of the technique has resulted in substantial savings on the deck installation costs for the platform’s owner, UNOCAL Indonesia.
Sinclair Knight Merz proposed the technique, with its cost effectiveness playing a key role in the Indonesian construction company, H&H Utama, winning the platform construction tender.
H&H Utama had commissioned Sinclair Knight Merz to carry out the process, mechanical, electrical, instrumentation and structural design of the platform’s double-deck topside.
It had also engaged the firm to engineer the loadout, seafastening and installation of the topside during its movement from the onshore fabrication facility to its installation on the offshore jacket – a cross-braced support tower through which piles are driven to anchor it to the seabed.
Sinclair Knight Merz Project Director, Wayne Gyde, said the conventional method for installing a platform offshore is to use a barge-mounted crane to initially lift the jacket, then the topside decks, off the transportation barge.
Mr Gyde said the ‘floatover’ method was a much more cost-effective way of installing the topside.
With this method, the transportation barge is fitted with two skid beams running lengthways along its deck and cantilevered over its stern.
The prefabricated deck is skidded directly onto the barge from the land and transported out to the jacket, where it is moved out over the cantilever beams while the barge is trimmed with water ballast.
The deck is then floated over the jacket and lowered into place using the falling tide and ballasting down of the barge.
'We successfully installed the new CPP2 platform at Yakin using this approach,' Mr Gyde said.
The new four-legged-jacket, double-deck topside platform measures 19 x 13 x 20 metres in height and is linked by a 20-metre bridge to the existing Yakin CPP1 platform.
The new platform will separate 10,000 barrels per day of wellstream oil and water, and 10 MMSCFD (million cubic feet per day) of associated natural gas.
It supports two 1200-kW gas engine powered generators to drive the downhole pumps, and a three-stage gas engine driven compressor with a capacity of eight MMSCFD delivered at 750 psi to export gas ashore and provide downhole gas lift.
Also on board are an electrical control room, shipping pumps, meters and water treatment and safety equipment, with space allowed for future equipment requirements.
The entire topside structure, excluding the bridge, generators, compressor and some minor equipment items, was prefabricated onshore and transported offshore in one piece.
'We used AutoPlant 3D modelling software to coordinate and integrate all the disciplines involved in designing the topside decks,' Mr Gyde said.
'This allowed all members of the design team to see where structural elements and plant were located, and to check and resolve potential clashes where there were two or more competitors for the same space,' he said.
'We also made extensive use of a project-wide Extranet that we created and hosted, to coordinate communications and operations between design offices in Auckland, Wellington and Melbourne, with our Indonesian offices in Jakarta and Balikpapan, our clients H&H Utama and Unocal, and with equipment suppliers.
'Effectively, the Extranet was the project-wide filing system for design related files and correspondence.
'I believe that, overall, the Yakin Project amply demonstrated our ability to successfully integrate a multi-disciplinary team and deliver world class skills to the local Indonesian oil and gas industry, while saving money for our clients,' Mr Gyde said.