Data from: Using controlled subsurface releases to investigate the effect of leak variation on above-ground natural gas detection

Pipelines transport natural gas (NG) in all stages between production and
the end user. The NG composition, pipeline depth, and pressure vary
significantly between extraction and consumption. As methane (CH4­), the
primary component of NG is both explosive and a potent greenhouse gas, NG
leaks from underground pipelines pose both a safety and environmental
threat. Leaks are typically found when an observer detects a CH4
enhancement as they pass through the downwind above-ground NG plume. The
likelihood of detecting a plume depends, in part, on the size of the
plume, which is contingent on both environmental conditions and intrinsic
characteristics of the leak. To investigate the effects of leak
characteristics, this study uses controlled NG release experiments to
observe how the above-ground plume width changes with changes in the gas
composition of the NG, leak rate, and depth of the subsurface emission.
Results show that plume width generally decreases when heavier
hydrocarbons are present, the leak rate is reduced, and as leak depth
decreases from 0.9 to 0.6 m. The above surface CH4 plume is undetectable
when leaks are 1.8 m deep. As most survey methods typically prioritize
leaks based on the leak size, this study shows that the effect of NG
density on above-ground plume width is only 4%, equivalent to the effect
of leak rate. This suggests that reported leaks in areas with heavier
hydrocarbons could currently be missed or underestimated. Furthermore,
this study shows that leaks from pipelines laid in covers meeting minimum
depth requirements of 0.9 m could be easier to detect compared to those
buried shallower. Overall, this study illustrates that leak survey
protocols for flowlines and gathering lines should be different from
distribution pipelines and tailored to the compositions of the transported
NG to report emissions accurately.