Aker BP has started drilling an interesting well (25/2-23A) in PL873, where Equinor (40%) and Lotos (20%) are partners. The first hole will be drilled in the Eocene Frigg sandstone in an attempt to find mobile oil in the depleted gas reservoir of the Øst Frigg field, followed by deepening of the well to test the Middle Jurassic Tarbert Fm of the Grefselkollen prospect.
The Øst Frigg field produced 58 MMboe of gas from 1988 to 1997.
Frigg oil
It is well known that the Frigg field and its satellites were characterised by an oil rim, even though the oil was never produced. In 2019, Equinor drilled a well in the Frigg field (UK 10/01b-6) to investigate remaining gas and oil reserves and presumably found that although the gas water contact had moved upwards significantly during production, the oil zone was still in the same depth range where it was prior to onset of production. The Frigg oil rim is about 10 m.
The oil could be trapped below cemented sands – is there a similarity with the Liatårnet accumulation? – or beneath finer-grained deposits that form part of the submarine fan system.
It is likely that Aker BP is after the Øst Frigg oil rim, with probably the main question being how laterally extensive the oil rim is, as well as how mobile. Is it pockets of oil trapped below local fine-grained layers or cemented sands, or is it still a fairly continuous interval? In case of positive results obtained in the pilot hole, the company aims to drill a horizontal well to further test the oil rim.
Tarbert
Once the Frigg sandstone has been tested, the company aims to deepen the well and targets the Grefselkollen prospect that has been identified in a Tarbert Fm reservoir of the Middle Jurassic Brent Group. It will not be the first time the Brent is being drilled in the area.
The Lille Frigg gas and oil field just north of Øst Frigg produced 22 MMboe from Brent sandstones until it was shut in in 1999, and the Fulla discovery contains 66 MMboe (mainly gas) in Ness Fm sandstones. Both Lille Frigg and Fulla are considered to be (re)developed as part of the greater North of Alvheim project, of which the Grefselkollen prospect and the oil in Øst Frigg will no doubt form part of too if successful.
HENK KOMBRINK
