Troll under pressure

As gas is produced on the giant Troll field, pressure in the reservoir drops. Pressure on the platform is lowered to help the gas move up and compressors are used to keep it moving.

Vast volumes

Troll already has two compressors, which will now be joined by compressor numbers three and four. These two compressors will boost recovery from the giant field by 83 billion standard cubic metres of gas - 522 million barrels of oil equivalent. That’s more than Aasta Hansteen and Valemon put together.

The compressor module was built at Aibel's yard in Thailand, and following a short stop in Haugesund, it is now in place on Troll A.

“The new module was lifted into place in a safe and sound manner. This has been planned for a long time, and it is therefore positive that we have reached this milestone, which is important for Troll A's gas deliveries over the next 50 years. Installing new modules weighing a total of more than 6,000 tonnes on an existing platform in operation is a huge task,” says Knut Solemslie, production manager on Troll A.

The project will ensure a daily export capacity of 120 million standard cubic metres of gas and annual production of 30 billion standard cubic metres.

“This is equivalent to the consumption of more than 10 million European households. The project is therefore an important contributor to the European gas market. It will also be possible to extract the gas more quickly, while also increasing the technical lifetime of Troll A,” says Tone Kristin Børslid, asset owner representative for the project.

Statoil currently has high pressure on low pressure. In all, the new compressors on Troll, Kvitebjørn, Åsgard, Kristin, Gullfaks and Heidrun will contribute more than 1.2 billion barrels of additional oil equivalent. A giant field in itself, just from enhanced recovery.

Global project

The project consists of three different modules. Aibel, the main supplier for the Troll compressor project, built one module in Thailand and two in Haugesund.

Last summer, the EIT module (electrical, instrument and telecom) from Haugesund was lifted on board Troll. The two next modules will be installed this summer.

Yet another module will be lifted on board a few weeks later. The IUM module (integrated utility module) was prefabricated in Poland and assembled in Haugesund, where the equipment was also installed. It weighs 1,800 tonnes.

Powerful power measures

The two new compressors on Troll A will be supplied with power from shore, more specifically from Kollsnes in Hordaland county, Norway. The two compressors can deliver an output of 50 megawatts each when in maximum operation mode.

Statoil has been granted a licence for this and the power grid has been reinforced in order to deliver the power needed by the compressors.

While the compressor module was en route from Thailand, power cables were laid from Troll A to shore. Five cables, each totalling about 70 kilometres, were laid between Kollsnes and the platform. Four of these cables are direct current (DC) and were installed in pairs.

“A transformer station has been constructed at Kollsnes which converts alternating current into direct current to reduce energy loss when the electricity is transported over long distances. On Troll A, the direct current is converted back into alternating current,” says marine installation manager Tom R. Guttormsen.

The final cable is an alternating current cable with fibre optics which will back up existing power deliveries to the platform, and will also provide the possibility of additional signal transmission between Kollsnes and Troll A.

The first cable was connected to the Troll A platform on 21 April. The installation of cables toward shore began afterwards. The work is carried out under an ABB contract with the Lewek Connector vessel, which is operated by EMAS. Lewek Connector is one of the largest and most modern cable installation vessels in the world.