Getting to the bottom of it

28.06.2017
“Integrating all available data to detect possible degrees of freedom for formulating new hypotheses was the key to success,” says Hans Christen Rønnevik. This approach allowed him to spot the geological potential of the Utsira High in the North Sea.

| Alice Ølberg Bore

Noted. The Utsira High discoveries are very significant for the further development of specialist expertise in Norway’s oil sector, believes Hans Christen Rønnevik. He says they will “occupy a key place in efforts to reduce the crisis in the industry and to secure jobs for the future.” (Archive photo: Emile Ashley)

Noted.
The Utsira High discoveries are very significant for the further development of specialist expertise in Norway’s oil sector, believes Hans Christen Rønnevik. He says they will “occupy a key place in efforts to reduce the crisis in the industry and to secure jobs for the future.”
(Archive photo: Emile Ashley)

 

The southern part of this area had been sporadically investigated by most of the big companies since 1967,” explains Rønnevik, former exploration manager at Lundin Norway.

“This meant large amounts of geological information were available, which we were able to utilise as the basis for a new interpretation.”

He adds that the subsequent discoveries on the Utsira High introduced broadband geophysics to the NCS, and this methodology has since become standard there.

The first big find in the area was made in the Luno prospect during 2007, renamed Edvard Grieg when the plan for development and operation (PDO) received approval in 2012.

With estimated recoverable oil reserves exceeding 200 million barrels (32 million standard cubic metres), this discovery converted the nearby Avaldsnes structure to a low-risk prospect.

Lundin’s 16/2-6 (“Avaldsnes”) well in 2010 discovered the giant field now called Johan Sverdrup. Holding some 2.8 billion barrels of oil, its peak daily output could reach 660 000 barrels.

 

Concept

Rønnevik explains that the exploration concept for Utsira High South was a big accumulation with a oil zone 40-50 metres thick under a gas cap less than 1 950 metres beneath sea level.

The Edvard Grieg and Johan Sverdrup discoveries have shown oil/water contacts down towards this level. They have no gas cap and are thereby undersaturated.

However, the level of undersaturation in the Johan Sverdrup crude is considerably greater than for the genetically similar oil in the Edvard Grieg formation.

Predrilling analysis indicated that the Johan Sverdrup structure was formed 1.5 million years ago. The discovery shows that oil-filling has been very rapid and is still under way.

Edvard Grieg comprises landdeposited Jurassic/Triassic sandstones and conglomerates with relatively good properties. Such reservoir rocks have not been encountered before on the NCS.

Wells drilled in Johan Sverdrup have found very good reservoir properties in the Upper, Middle and Lower Jurassic sandstone sequences deposited in shallow seawater and along the shoreline.

 

Extensive

“This discovery covers a very big area and called for extensive appraisal drilling,” says Rønnevik. “We took cores, analysed and tested.

“That was essential for acquiring a quick grasp of the local geology and to provide a solid factual basis for the models on which the development plans were to be built.”

He emphasises that each well has been very significant for amending and adjusting the models. A crucial factor is that the people who formulated the hypotheses were also involved in updating during the operational work.

“Putting together technically diverse teams of people with the ability and commitment to reach a collective result is important,” Rønnevik emphasises.

“Operational activity must rest on fact-based learning and steady improvements in practice. Relationships between the people involved are crucial.”

He says that the Utsira High discoveries are very significant for the further development of specialist expertise in Norway’s oil sector. They will “occupy a key place in efforts to reduce the crisis in the industry and to secure jobs for the future.”

 

Facts about Johan Sverdrup

  • Oil field on the Utsira High in the Norwegian North Sea, 40 kilometres south of Grane and 65 kilometres north-east of Sleipner.
  • Scheduled to come on stream on 1 December 2019.
  • 70 per cent of the contracts awarded to companies with a Norwegian address.
  • Profitable at an oil price as low as USD 20 per barrel.
  • Will yield NOK 1 350 billion in revenues over a 50-year producing life.
  • Tax revenues will total USD 670 billion.
  • Peak daily production will be 440 000 barrels (70 000 scm) of oil and six million scm of gas for phase one, and 660 000 barrels (105 000 scm) plus 10 million scm for the full field.
  • Water depth on the field is about 110 metres.
  • Reservoir depth is about 1 900 metres.
  • Covers about 200 square kilometres.
  • Chosen solution for the first development stage is a field centre with four dedicated platforms for quarters, processing, drilling and risers, all linked by bridges.
  • Drilling platform with 48 well slots is designed for simultaneous drilling, well intervention and production.
  • Power from shore will be used throughout the field’s producing life. Phase two, due on stream in 2022, includes power from shore for other developments in the Utsira High area.
  • Oil resources being developed in phase one lie in continuous Upper Triassic and Lower Cretaceous sandstone reservoirs. However, the bulk of the crude is found in Upper Jurassic intra-Draupne sandstones originating from the basement high in Utsira High South. The remainder lies in the Statfjord and Vestland Group as well as in Viking Group spiculites. Oil has also been proven in Zechstein carbonates.
  • Water injection will be utilised as pressure support and gas lift in the production wells, along with other measures for improving oil recovery. Producers will be placed high in the thickest parts of the reservoirs, with injection wells close to the oil/water contact. Producers and injectors are four-five kilometres apart.
  • Stabilised oil travels from the riser platform to the Mongstad terminal near Bergen through a new pipeline tied into rock caverns. Gas goes from the same platform to the Kårstø terminal north of Stavanger via a new pipeline tied into the rich-gas arm of the Statpipe system west of Karmøy island.

Topics: Geology