How large is a troll?

Troll is by far the biggest petroleum field on the NCS, well over twice the size of the next largest measured by resources. It contains both gas and oil, with the former accounting for 80 per cent of the quantity. But it is important to remember that the oil reserves are also considerable – enough on their own for Troll to rank as the 10th largest oil field on the NCS.

Area, depth and wells

The reservoir in Troll lies about 1 300 metres beneath sea level and comprises sediments known as shallow marine sandstones. These have been deposited in relatively shallow water and well sorted by currents and waves.

Extending across four North Sea blocks, the whole field covers just over 700 square kilometres.[REMOVE]Fotnote: Troll Field: Norway’s Giant Offshore Gas Field, 1992, Giant Oil and Gas Fields of the Decade 1978-1988. That corresponds to about 100 000 football pitches, three times the 241 square kilometres covered by the enlarged City of Stavanger and 1.5 times the size of Oslo.

Its porosity – in other words, the pore spaces between the sand grains – is about 30 per cent and the column from the top of the reservoir to the beginning of the underlying aquifer measures more than 200 metres. At 31 December 2021, almost 300 production wells have been drilled. These contained 600 sidetracks – additional wells drilled out from a main borehole. More than two million metres of well paths penetrate the reservoir – about the distance from Stavanger to Barcelona.[REMOVE]Fotnote: https://www.norskpetroleum.no/en/facts/field/troll/.

NOK 215 billion had been invested in the field by 2019. It is being produced from three platforms, well over 50 subsea templates and a total of 85 permanent installations.

World’s tallest moveable structure

The Troll platforms vary in design. While the A structure is a fixed concrete Condeep type, Troll B and C are floaters with hulls in concrete and steel respectively. Of these, Troll A is the unit most often associated with the field. It has been described as the “eighth wonder of the world”, and spectacular scenes were witnessed when it was towed out to the North Sea in 1995. It still holds the record as the tallest structure ever moved.

Troll A was the last concrete gravity base structure (GBS) – which sits on the seabed through its own weight – and extends 472 metres from bottom to top. That includes the 369-metre GBS.

The latter was built over more than four years at Hinnavågen in Stavanger and Vats further north, and contains 250 000 cubic metres of concrete. It also holds 100 000 tonnes of reinforcement steel, enough to built roughly 13 Eiffel Towers. Tow-out to the field took seven days and the platform was finally positioned in 302 metres of water on 17 May 1995.

Energy

The quantity of gas in the Troll field is put at 1 437 Mscm oe. But  what does that mean? Let us break down numbers and text so that they become something easier to understand.[REMOVE]Fotnote: https://www.norskpetroleum.no/en/facts/field/troll/, accessed 21 February 2022. The Norwegian Petroleum Directorate’s energy calculator has been used for the conversions, https://www.norskpetroleum.no/en/calculator/about-energy-calculator/.

• M stands for million (10⁶)
• scm stands for standard cubic metre, a common way of specifying gas and oil volumes standardised at 15°C and normal atmospheric pressure (1 013.25 hectopascals (hPa))
• oe stands for oil equivalent – in other words, the quantity of oil which will give the equivalent amount of energy as the gas.

To convert 1 437 Mscm oe to the physical amount of gas in Troll, multiply by 1 000. In other words, one unit of oil by volume has the same amount of energy as 1 000 units of gas by volume.

This means that Troll contains 1 437 billion scm of gas, or 1 437 giga scm (Gsm).

Since gas volume may not be that easy for an ordinary consumer to relate to, we can continue with the conversion. Expressing the amount of gas in Troll in kilowatt-hours (kWh) gives us:

• 1 596 650 7000 000 kWh
• 15 967 TWh (terawatt-hours)
• 16 PWh (petawatt-hours).

This is a purely theoretical exercise. A power station converting gas into electricity, for example, will not have an energy efficiency of 100 per cent.

But how much are all these kilowatt-hours? Let us look at some reference sizes.[REMOVE]Fotnote: These figures have been acquired on 22 February 2022) from Norway’s forbrukerguiden.no, https://energifaktanorge.no/en/norsk-energibruk/; ssb.no, https://www.ssb.no/energi-og-industri/artikler-og-publikasjoner/vi-bruker-mindre-strom-hjemme;  https://www.eea.europa.eu/ims/primary-and-final-energy-consumption-1; https://www.nve.no/energi/energisystem/kraftproduksjon/; https://ccaf.io/cbeci/index, checked 21 February 2022.

In other words, the theoretical amount of energy in the Troll gas corresponds to almost 100 years of Norwegian electricity generation and almost a billion years of consumption by an average household in Norway.

Another way of looking at this is to assume you had turned on a 350-watt electric panel heater when the Earth first formed 4.56 billion years ago. By today, it would only have just have used the same amount of energy found in Troll (although the warranty on the heater is unlikely to have lasted that long).

Alternatively, generating the energy content of Troll with solar panels over the 70 years which the field is expected to remain on stream would require the panels to cover an area of 320 square kilometres – assuming an output of 150 watts per square kilometre and sunshine for 12 hours every day.

Licensees and decimals

All fields on the NCS have more than one licensee. Equinor is operator for Troll, but not the biggest licensee. At 31 December 2021, holdings in the field were distributed as follows.

It is easy to assume that so many places after the decimal point are unnecessary. But a difference of 0.00001 percentage points on Troll corresponds to gas with an energy content which equals the electricity consumption of an average Norwegian household for a century.

However, Troll is by no means the world’s largest petroleum deposit. That honour goes to the Ghawar field in Saudi Arabia, which is said to contain 22 Gscm oe or 15 times more than Troll’s gas content.