Figure 1.17: The two structural highs, Avaldsnes and Aldous Major South, on Block 16/2 in a water depth of 115m, about 140 km west of Stavanger, Norway, were explored as two separate prospects with two different wells, 16/2-6 and 16/2- 8, respectively. Well 16/2-8 met a 65m oil column, whereas well 16/2-6 proved a 17m oil column. The wells proved to belong to the same accumulation with the same oil-water contact, pressure regime, oil type and reservoir and the field was renamed Johan Sverdrup. The reservoir depth is about 1,900m. Aldous Major North is separated from the southern part by a major fault and does not contain a commercial discovery. (Well number 16/2-6 means that the well was drilled in Norwegian quadrant 16. Each quadrant is divided into 12 blocks, and this particular well was drilled in block 2 as the 6th well on that block.)
1.3.1.2 Unveiling the Secrets of Mysterious Johan Sverdrup
Late in 2007 Lundin Petroleum made an oil discovery in the Luno prospect, today known as the Edvard Grieg field, located in the Utsira High in the central North Sea. Te Utsira High is a large crystalline basement horst, flanked by the South Viking Graben to the west and the Stord Basin to the east. Te present structural configuration has been inherited from extensional tectonism which occurred in the late Palaeozoic, 250–200 million years ago. It is believed that deep weathering of the granitic landscape during the late Triassic, around 200 Ma, was followed by a marine transgression and deposition of sedimentary strata. A detailed and comprehensive exploration study was
initiated in the area around this discovery, as a result of which, in September 2010, Lundin drilled an exciting new well, 16/2-6, testing the Avaldsnes prospect, which also proved a great success.
In the summer of 2011 Statoil announced that their Aldous Major South 16/2-8 well had found oil on a nearby structural high and proved that the Lundin and Statoil wells had drilled into the same oil accumulation, with a saddle between the two highs. Since these discoveries constituted one single field, it was renamed Johan Sverdrup after the father of Norwegian parliamentarism. By 2015 more than 30 wells had been drilled to appraise
the size and reservoir quality of the field. In August 2015, the plan for development and production was approved by the Norwegian government. Statoil is the operator and the partners are Lundin Norway, Petoro, Det Norske and Maersk Oil. Te Johan Sverdrup field is ranked as one of the top five discoveries ever made in Norway, with estimated recoverable reserves of between 1.7 and 3 Bbo. But how could such a giant field in the mature part of
Figure 1.18: Johan Sverdrup geosection between selected wells, with different geological formations. The oil resources are located in a reservoir that consists of interconnected Late Triassic to Early Cretaceous sandstones. The majority of the resources occur in the intra-Draupne sandstones of the Viking Group, deposited in the Late Jurassic. In the eastern part of the field, the Viking Group contains Draupne shale, with the remaining oil resources found in sandstones in the Statford and Vestland Groups. In Norse mythology, Draupne is a gold ring owned by the Viking God Odin, which has the ability to multiply itself; every ninth night, eight new rings ‘drip’ from Draupne, each one of the same size and weight as the original. In this way, Draupne is an endless source of richness. The name is considered particularly appropriate in view of the Draupne Formation’s role as a prolific hydrocarbon source in the northern North Sea. In both age and depositional environment the Draupne Formation is equivalent to the UK Kimmeridge Clay Formation. To the south-east, the location of well 16/3-2, drilled in 1976 by Norsk Hydro some hundred metres off the oil column, is shown. Observe the scale of the geosections. The upper one has no vertical exaggeration, while the lower one has vertical exaggeration 33 times. Sequences of sedimentary rocks are subdivided on the basis of their lithology. Going from smaller to larger in scale, the main units recognised are bed, member, formation and group. For instance, the Viking Group is subdivided into five formations: the Heather, Draupne, Krossford, Fensford and the Sogneford Formations. The Draupne sandstone consists of unconsolidated very coarse to medium grained sands, with very few sedimentary structures. (Courtesy Statoil and licence partners Lundin Petroleum, Maersk Oil, Petoro, and Det Norske Oljeselskap.)
Geitungen 0.2 km Espevær High Røvær Basin Avaldsnes High 5 km (no vertical exaggeration) 16/2-19 Geitungen metres
1850 1900 1950 2000
NW 16/2-19 16/2-12 16/2-19A Espevær High 16/2-10 16/2-16 AT2 16/2-16 Røvær Basin 16/2-13A 16/2-13S 16/3-6 Avaldsnes High 16/3-4A 16/3-4 16/3-2 Group 5 km (vertical exaggeration: 33 x)
Hegre Group Statford Group Vestland Group Viking Group
SE N 0 2.5 5 km 16/3-2 NW-SE correlation section
14
0.2 km
Statoil
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