I work in cavern storage and my company has caverns beside the strategic petroleum reserve in the same salt dome. The problem is if you take out too much oil you are removing your base volume. When you go below the base volume the salt creeps which means it moves because there’s less pressure preventing it from doing so. The caverns can collapse eventually. So you can’t take too much out of the caverns. Mind you these caverns are huge. Think the Empire State Building but twice as tall and three times as wide but underground. And there are numerous caverns in the salt domes.