Methane and ethane emission quantifications from onshore oil and gas sites in Romania, using a tracer gas dispersion method

Site-specific methane (CH4) and ethane (C2H6) emission rates from the onshore oil and gas (O&G) sector in Romania were quantified, using the mobile tracer gas dispersion method. As part of the coordinated Romanian Methane Emission from Oil & Gas measurement campaign, this study supported the investigation of CH4 emissions from the O&G sector around Bucharest. CH4 emission rates measured at 200 O&G sites were highly skewed with a heavy tail and described by a CH4 emission factor (EF) with a 95% confidence interval (CI) equal to 0.53 [0.32; 0.79] kg h-1 site-1. Of the investigated sites, 53% showed CH4 emission rates below 1 kg h-1, whereas only 6% had emission rates higher than 80 kg h-1,with the highest being equal to 297 kg h-1. CH4 emission rates from oil wells were not correlated to CH4 production rates but were negatively correlated to the amount of wastewater produced. C2H6 emissions were investigated from 95 O&G sites, the emission rates of which were highly skewed with a heavy tail and described by a C2H6 EF with a 95% CI equal to 0.07 [0.04; 0.13] kg h-1 site-1. Almost 80% of the investigated sites showed C2H6 emission rates below 1 kg h-1, and 7% of them had emission rates higher than 9 kg h-1, with the highest being equal to 78 kg h-1. CH4 emission rates and EFs representing specific types of sites and geographical regions are provided in the manuscript. In terms of magnitude and distribution, these results are in line with published results from measurements at O&G sites in North America, and a natural gas field in the Netherlands. The CH4 EF calculated in this study is close to the lower range of the majority of values in the literature, whereas C2H6 EF is the lowest among the literature values. The study also provided site-specific C2H6-to-CH4 molar ratios in different regions around Bucharest.