The "heat map" for the Williston Basin can be found at this link.
It's really too small to say for sure, but I've never felt the Oliver oil field, north-northeast of Williston, or maybe east-northeast of Williston was all that good a field. But, wow, Kraken is proving me wrong.
I would put Oliver field into the Tier 2 basket but it looks like the Oliver field may be closer to a Tier 1. You know, having said that, all this stuff is relative. The Tier 1 fields will "get better" going forward with better technology, more experience, etc., so maybe Tier 1 fields remain the same and Tier 2 fields remain the same. It's just that Tier 2 fields will now look as good as Tier 1 fields in the early days of the boom. Idle rambling, but I don't think one can put the Oliver oil field in the same tier as the Parshall, or the Grail.
Having said that, the Kraken wells in Oliver oil field are very nice wells.
See these recently released Kraken wells and note Kraken has seven more permits for the same location.