Isotopic characterisation of methane emissions from oil and gas operation in Romania

Reducing methane emissions is an important goal of climate change mitigation policies. Recent studies focused on emissions from oil and gas industry, because fixing gas leaks presents a "no-regret" mitigation solution. Yet, uncertainties regarding the fossil fuel emission rates and locations, as well as temporal and spatial variability, are still large for individual source processes, in particular in regions without regular measurements. The Romanian Methane Emissions from Oil and gas (ROMEO) project brought 13 research teams to Romania in order to quantify emissions from this sector. Methane stable isotopes are widely used for source characterisation, but measurement data is lacking from many important geographical locations, such as Eastern Europe. 

A total of 380 air samples were collected in urban areas and around oil and gas extraction sites, from ground level vehicles and from an aircraft. There were measured for δ¹³C-CH₄ and δD-CH₄ using a continuous flow isotope ratio mass spectrometry (CF-IRMS) system. The results were analysed using the Keeling plot approach to derive source signatures at each sampled site. The source signatures obtained for 76 individual oil and gas operation sites range from -70.5 to -22.4 ‰ V-PDB, and from -252 to -144‰ V-SMOW, for δ¹³C and δD respectively. They show a large heterogeneity in δ¹³C, and more regularity in δD values. Variations are affected by the maturity of hydrocarbon deposits, and by different contributions from microbial and thermogenic gas. We will present how the signatures measured at the surface relate to the signatures found for larger plumes sampled from the aircraft. The results of the campaign in Bucharest city reveal a larger contribution from the waste system than fossil fuel fugitive emissions. 

The isotopic characterisation of methane emissions in this region will help to constrain the methane budget on a regional scale, and to improve national inventories.