In what was supposed to be the biggest contributor to the overall volumes found in the Iving discovery in 2019, two appraisal wells now suggest that the Triassic reservoir may not have lived up to its expectations.
A total volume for the Iving discovery was never released, but following the completion of exploration well 25/8-19S in 2019 the operator announced a volume range for the Triassic Skagerrak reservoir as being between 13 and 70 MMboe recoverable, adding that this interval offered the biggest in-place volumes.
The NPD press release now states that the results will lead to a downward adjustment, but it also says that it is too early to present an updated estimated volume for the discovery.
What did the wells find?
The purpose of drilling the 25/8-21S well was to drill the oil-water contact in the Skagerrak Formation. However, although the well did prove mostly oil in poor to good quality Skagerrak sandstones at two levels (a 30 m and 6 m column), a contact was not found. This may already indicate that the Skagerrak Fm is more challenging in terms of reservoir characteristics, or potentially thinner than expected.
Apart from oil the Triassic, a separate oil column of 50 m was found in poor reservoir quality basement rocks in which a contact wasn’t found either.
The 25/8-22S well drilled a 20 m gas overlying a 29 m oil column in moderate to good Skagerrak reservoirs, with pressure data suggesting that communication exists between all Skagerrak penetrations in the discovery.
Thin oil columns were also found by 25/8-22S in the Lower Jurassic Statfjord (two times 2 m) and the Heimdal sandstone (3 m).
Based on the reported findings, it seems that the main reason why the appraisal campaign disappointed is that the hydrocarbon columns are more fragmented than initially foreseen. As Henrik Jakobsen alluded to in his talk on the Iving discovery during the NCS Recent Discoveries talk in 2020, there was some hope that the combined Triassic and basement oil finds constituted one overall column.
From what has now been found, the Skagerrak is characterised by at least two separate columns, with the lowermost part not having sufficient reservoir quality to confirm mobile petroleum. This may also be the reason why the basement oil column was reported as being separate from the Skagerrak in well 22/8-21S.
These findings were probably the reason not to drill the planned 1000 m side-tracks from both appraisal wells. There is surely some work to do for Mol and partners in terms of defining a follow-up plan now that many thin columns seem to be the overall picture rather than just a nice tank of oil.
HENK KOMBRINK
