中国におけるシェールガス生産からのメタン排出量の評価：二層式移動測定アプローチ

China, holding the world's largest shale gas reserves, lacks precise data on methane emissions from its rapidly expanding production. We introduce a two-tiered mobile measurement approach, using a mobile laboratory to measure methane concentrations across 125 well pads (approximately 750 wells) distributed among four major production blocks (Changning, Weiyuan, Fuling, and Luzhou). These blocks contributed 84% of China's total shale gas production in 2023, providing the first comprehensive ground-level measurements. Stationary downwind monitoring of well pads revealed emission rates from 0.002 to 98.86 kg/h, validated through mobile observations of methane concentrations across the region. Notably, emissions were highly concentrated, with 89% originating from just 10% of the well pads. For 2023, the extrapolated methane emissions from China's shale gas production were estimated at 16,842 t (6,444-29,991 t, 95% CI), corresponding to a methane leakage rate of 0.10% (0.04%-0.17%, 95% CI). This rate is lower than major U.S. fields and similar to that of U.S. dry gas fields. Our research identifies gas lift venting, incomplete combustion from compressors, and process venting as significant sources of super-emissions in China's shale gas upstream production chain. The methodology employed, based on comprehensive and targeted field measurements, demonstrates its effectiveness in providing a scientific basis for formulating precise and effective regulatory policies on methane emissions.