Companies do have health and safety groups out there working on these things. Of course, the bigger the company the slower, more inefficient, and incompetent they tend to be. Prices can range - some things can be patched, but many times the reason for the leak is age and it requires a new piece of equipment. So, there you would have permitting to handle, expensing the equipment at either the field level or, most likely, well level, which would kill the "economic-ness" of said well/well pad which never sits well with a company and may make them rethink it and just plug the wells - equipment could be low to high hundreds of thousands - really depends on the piece and size. In terms of frequency, People are fixing these things daily, small projects to fieldwide initiatives. In terms of someplace like Turkmenistan, anything can be fixed with money. In that part of the world, your best bet is financial incentive. I mean, it is unethical, but just pay the "expediting fee" for the local warlord/mayor/president - usually a "donation" to an orphanage or fund that doesn't really exist. The cancer rates thing is interesting - the well in question is possibly a Marathon well. Their record isn't the greatest (Look into Paw Creek, NC and Marathon's "small leak" at their terminals there). No scientific data on this at hand, but as a person who works in oil and gas and chemicals with an oddly high number of friends who have had some type of severe cancers, I would say this would be hugely helpful to the general public.

> - If it's relatively cheap and easy, why hasn't it been done in the past already?

It provided no benefit that the shareholders cared about.

There's a long history of resource-exploitation companies doing horrible things to the environment, and conveniently going bankrupt when they are near the end of operations. The system does not prevent that behavior well enough, nor does it punish the people who do it.

Our economic system has no built in incentives to stop these leaks. Considering how massive these leaks are, the budget to plug them shouldn't be a consideration. We're ruining our planet's livability with leaks like this, but since it's not profitable for anyone to do anything about it, we won't do it until there's enough political will behind it.