This is not what an oil well looks like, and the article doesn't help with phrasing like "depleted cavern". An oil well is not a big cave filled with black, bub

This is not what an oil well looks like, and the article doesn't help with phrasing like "depleted cavern". An oil well is not a big cave filled with black, bubbling oil and a big "straw" poked into it. The hydrocarbons are held in the porosity of the rock, and pressures (both natural and introduced) force them to the wellbore. A very poor sponge is a better visible analogy, but even that over-represents the voids.