Marginal methane emission estimation from the natural gas system

Abstract

A new cause-based approach was used to estimate the change in methane emissions from the natural gas system resulting from a change in throughput. The analysis builds upon prior work (Mac Kinnon et al., 2018) positing that a cause-based, marginal approach to estimating methane emission impacts of reducing or increasing natural gas use was more accurate than assuming that methane emission vary one-for-one with throughput. The goal of this work is to determine the relationship between methane emissions and changes in throughput both over short time horizons where the gas infrastructure is fixed and over time periods where system expansion (or retirement) and technological improvements via component replacement occur. The results show that methane emissions change with throughput but the relative change in emissions is less than the relative change in throughput. There are many components (emissions sources) in the natural gas system that emit the same amount of methane to the atmosphere regardless of their operational mode; meaning some emissions sources have no or only partial dependence on throughput. As a result, reducing natural gas consumption in the future will not yield a directly proportional reduction in the methane emissions. It is believed that the results of this study will help energy policymakers to understand better the effect of policies aimed at reducing natural gas use on greenhouse gas (GHG) emissions and where such policies should be applied (e.g. system operator or end user).