«We’ve drilled a volcano»Steve Thomas, Lundin, winner best talk Exploration Revived (Photo NPF)

«We’ve drilled a volcano»

Steve Thomas from Lundin was chosen as the winner for best talk of the NPF’s Exploration Revived conference with his presentation about the Silfari well results.

Well 6307/1-1S was drilled by Lundin Norway and finished in December 2018 (Read also “No reservoir no oil”). The target of the exploration well was the Silfari dome in the Froan Basin in the Norwegian Sea.

The location of the Silfari dome in the Froan Basin © Lundin Norway

Play test

The Silfari well was a play test in several ways. In order to charge the Silfari structure with hydrocarbons, a local mature Paleozoic source rock had to be present in the Froan Basin.

On seismic the Silfari dome is a faulty irregular feature and pre-drill Lundin thought it was a Permian carbonate buildup or a hydrothermal complex or a combination of those namely a hydrothermally altered carbonate buildup. Analogues of hydrothermally dolomitized buildups are well known from the Wegener Halvø Formation in Greenland (Scholle et al., 1991; Stemmerik et al.,1993 ).

Massive Wegener Halvø carbonate buildups passing laterally into well-bedded flank deposits, Devondal Wegener Halvø, Greenland (Sørensen et al., 2008)

The Permian play is underexplored in Mid Norway but well 6407/10-3 had oil shows in the Permian. Further south Permian carbonate reservoirs buildup reservoirs are present as seen in several penetrations in the Utsira High and from the Lille Prinsen discovery. The Utsira High area was situated on the margin of the Permian Zechtstein Basin (Sorento et al., 2018).

The additional targets of the well were a Jurassic closure at different reservoir levels and the lower Tertiary Egga fan. If there was any oil generated in the Froan Basin it was most likely trapped at one of these levels.

No carbonate buildup but…

In the Jurassic section, good stacked reservoirs were encountered from the Not Formation and down but there were no signs of hydrocarbons.

In the main target no carbonates or hydrocarbons were found but tight, very hard, crystalline igneous rocks with very high Gamma Ray. At one interval the GR dropped, and a core was taken. This core consisted mainly of syenite, barite and calcite so there must have been some carbonate in the system.

At the bottom of the well, they drilled into clastics again.

Lundin is now working the data and does not want to write off the Froan Basin yet although Steve Thomas admitted that the petroleum system story is not looking very good.