Along some particularly leaky production paths methane emissions are so great that the impact is greater than coal over 100 year timescale. For example, some parts of NM Permian have a 9% (!) leakage rate. When combusted methane releases about half the amount of CO2 that coal does. The eGHG potential of methane is 20x CO2 over 100 year timescale, so you have to add 180% to the total GHG potential, making it 40% worse than coal w/o even considering other leakage along the pipeline.
https://sustainability.stanford.edu/news/methane-leaks-are-f...