*Who will clean up the 'billion-dollar mess' of abandoned US oil wells?*

Collapse, by Jared Diamond, explains how the same thing happens with mines: when the mine becomes unprofitable to operate, there is no money left in the company that owns it to clean it up.

Often the actual ownership of wells is left in small companies that can be allowed to go bankrupt, while the profits are in the megacorporations that buy from those small companies. Those will never go bankrupt.

A carbon tax could solve the problem. Part of the tax money could pay for closing wells. Of course, the tax should be a lot bigger than that, because its purpose is also to encourage switching to renewable energy.