25% certainly does seem high, but I'm not an experienced mud logger so I couldn't say for sure what it means.
It pretty clearly represents a fairly sizeable influx of oil into the wellbore, though. It's a long way from reservoir to surface, it could take up to an hour for mud to make the round trip, getting swished about all the way, so for there still to be 25% oil concentration by the time it reaches the surface, there must have been a lot of it to start with.
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