Abnormal tank emissions in the Permian Basin identified using ethane to methane ratios

There has been increasing interest in quantifying methane (CH4) emissions from a view toward mitigation. Accordingly, ground-based sampling of oil and gas production sites in the Permian Basin was carried out in January and October 2020. Molar ethane to methane ratios (EMRs) were quantified, which may be used to distinguish emissions from particular sources, such as produced gas and oil tank flashing. The geometric mean EMR for 100 observations was 18 (±2)%, while source specific EMRs showed that sites where emissions were attributed to a tank produced much higher EMRs averaging 47%. Sites with other noticeable sources such as compressors, pneumatics, and separators had lower and less variable EMRs. Tanks displayed distinct behavior with EMRs between 10% and 21% producing CH4 emissions >30× higher than tanks with EMRs >21%. This observation supports the hypothesis that high emission rate tank sources are often caused by separator malfunctions that leak produced gas through liquids storage tanks.