Oilfield found in London borough (5)
I believe the answer is:
brent
'london borough' is the definition.
(I've seen this before)
I don't understand the rest of the clue.
Can you help me to learn more?
(Other definitions for brent that I've seen before include "West London area" , "kind of 10 [GEESE]" , "Type of goose - London borough" , "West London borough" , "Small migratory goose" .)