Abstract
Coal seam gas (CSG) accounts for about one-quarter of natural gas production in Australia and rapidly increasing amounts globally. This is the first study worldwide using airborne measurement techniques to quantify methane (CH4) emissions from a producing CSG field: the Surat Basin, Queensland, Australia. Spatially resolved CH4 emissions were quantified from all major sources based on top-down (TD) and bottom-up (BU) approaches, the latter using Australia's UNFCCC reporting workflow. Based on our TD-validated BU inventory, CSG sources emit about 0.4% of the produced gas, comparable to onshore dry gas fields in the USA and The Netherlands, but substantially smaller than in other onshore regions, especially those where oil is co-produced (wet gas). The CSG CH4 emission per unit of gas production determined in this study is two to three times higher than existing inventories for the region. Our results indicate that the BU emission factors for feedlots and grazing cattle need review, possibly requiring an increase for Queensland's conditions. In some subregions, the BU estimate for gathering and boosting stations is potentially too high. The results from our iterative BU inventory process, which feeds into TD data, illustrate how global characterization of CH4 emissions could be improved by incorporating empirical TD verification surveys into national reporting.This article is part of a discussion meeting issue ‘Rising methane: is warming feeding warming? (part 1)’.
Highlights
Methane (CH4) is the second most important anthropogenic greenhouse gas, contributing about 25% to the global warming experienced to date [1,2]
Governments around the world including Canada, Colombia, Mexico and the USA have already committed to substantial CH4 emission mitigation from the oil and gas (O&G) industry supply chain in parallel to CH4 intensity targets set by that industry [11]
In the subregions where the TD estimates exceed the BU (BU/TD 0–50%, electronic supplementary material, figure SF27), there are four subdomains where coal seam gas (CSG) gathering and boosting (G&B) contribute greater than 20% of the subregion emissions (16_09, 16_10, 19_03, and 19_04)
Summary
Methane (CH4) is the second most important anthropogenic greenhouse gas, contributing about 25% to the global warming experienced to date [1,2]. Global atmospheric CH4 mole fractions have increased from around 700 parts per billion (ppb) in the pre-industrial era [3] to around 1870 ppb in 2020 [4], increasing more than three times as fast as CO2 [5,6]. Substantial emission cuts along the oil and gas (O&G) industry supply chain can be achieved at no net monetary cost [9], especially when factoring in the social cost of CH4 [10]. Governments around the world including Canada, Colombia, Mexico and the USA have already committed to substantial CH4 emission mitigation from the O&G industry supply chain in parallel to CH4 intensity targets set by that industry [11]
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