Well brought up but lacking refinement (5,3)

I believe the answer is:

crude oil

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But I can't explain it at all! Could you help me understand?

(Other definitions for crude oil that I've seen before include "output from rig" , "Source of fuel" , "From which petrol is made" , "that has boring producers?" , "Unrefined petroleum" .)

I've seen this clue in The Globe and Mail.

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