That study starts with the ridiculous assumption of a 3.6 -7.9% leak rate in fracked gas. By their own admission, the data they used was spotty for leak rates during drill completion, and transport. Study is also outdated (2011) with regards to technological improvements of frack wells.

A leak rate confirmed by NOAA and Lawrence Berkeley: https://cleantechnica.com/2013/12/01/natural-gas-production-...

There's also a defence of the original study https://link.springer.com/article/10.1007/s10584-012-0401-0#...