Methane emissions from shale gas production sites in southern Sichuan, China: A field trial of methods

Abstract

Shale gas is an important alternative natural gas source that can meet China's growing energy demand. However, methane emissions during shale gas production could largely determine whether it could be considered as a bridging clean energy source. In this study, we performed methane emission measurements using three methods (on-site optical gas imaging, on-site methane patrolling, and downwind measurement) at shale gas production sites in Sichuan province, China, covering 18 well sites with 81 wells. The results showed that flowback water tanks were the major methane sources, with valves, separators, chemical injection pumps, and pneumatic controllers as other sources. The methane concentrations inside the 18 sites ranged from 1.42 to 459 μmol mol−1, with over 59% of the sites having the highest concentration less than 50 μmol mol−1. The optical gas imaging method, with its low detection limit over 5000 μmol mol−1, could not capture the emission effectively. The three successful downwind measurements resulted in site level emission rates between 0.02 and 0.17 kg h−1. When divided by the number of wells at each site, the emission intensity was 4%–28% of the wellhead emission factor for natural gas production in China. More measurements are required to better quantify methane emissions from shale gas sites in China. For sites in mountainous regions or long-term low-wind regions, detection methods other than downwind measurements should be suitable for quantifying site-level emissions.