The most common and most likely answer to this crossword clue is the 8 letter word BOREHOLE
I've seen this crossword clue in The Guardian
B
O
R
E
H
O
L
E
Buddy explains!

The straight part
We know that "Well" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case well = borehole.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does BOREHOLE mean?
BOREHOLE noun- A hole bored into the ground to collect samples for analysis or to extract oil or water.
- To bore a hole of this kind (in).