I believe nuclear charges are not only used to stop spill but also to release natural resources. However I did not find a reputable source of information to confirm that.
You might be thinking of the natural gas stimulation experiments performed by the US in the 70s[1]. From that article, "it was found that the three blast cavities had not connected as hoped, and the resulting gas still contained unacceptable levels of radionuclides" so it never went past the experimentation phase.
[1] https://en.wikipedia.org/wiki/Operation_Plowshare#Natural_ga...