In 1971, NAM drilled a dry exploration well (F03-02) just 500 m away from where Dana is currently drilling F03-09 in licence F03C.
It seems unlikely that the target of the well drilled 50 years ago is different from the well currently being drilled though. The main geological feature in the area is a Zechstein salt dome, with the Upper Cretaceous Chalk overlying the salt dome being the main candidate as a prospective reservoir.
F03-02 was drilled to 2,150 m, terminating in the Zechstein after drilling through almost 250 m of Chalk. No hydrocarbons were found except from a comment on the composite log saying that oil bleeding was observed at the very top of the Chalk section.
When looking at the cross-section shown below, it is clear that the F03-02 well was drilled slightly off the crest of the salt dome. The same can be seen on the map above. We also tested this compiling multiple cross-sections using this useful tool provided by TNO – Geological Survey of the Netherlands, with which cross-sections can be drawn along any random profile in the Dutch on- and offshore and using a variety of subsurface datasets.
Was the F03-02 well drilled off crest deliberately? Let’s at the moment assume it was, as it could reflect the minimum volume required for a find to be commercial in those days. This is seen in other places in the North Sea too. For instance, the Ilder well drilled by Harbour last year tested the very crest of a salt-pinned dome where two previous wells had already drilled the flanks.
As there is much more infrastructure in place and oil prices at the moment are buoyant, it is probably attractive to Dana to now explore the very crest of the structure, even though F03-02 already provides a clear cut-off in terms of the P10 volume.
Besides the Chalk prospect, which is probably the one named Bokje, the second prospect mentioned is Anteater. Although it is not entirely clear which interval this prospect has been defined in, it may be a shallow gas prospect in the overburden of Bokje. This TNO document mentions that a “good” gas show was observed in the F03-02 well, which is also associated with a bright spot.
HENK KOMBRINK
