Monitoring and investigating methane leakage in coal gas production

Abstract

The Qinshui Basin in Shanxi Province in northern China is currently the largest production area of coal bed methane (CBM) in China. For this study, methane (CH4) measurements were collected from 113 wellheads to determine primary gas leakage locations. The results indicate that the leakage is primarily from water outlets and tubing; three leakage points accounted for 95.79% of the total measured gas. With respect to measurement variability, the standard deviation for gas measurements of the tubing was the largest at 12.28. Wells with good geological conditions and scientific management exhibited very low leakage. In contrast, wells with unfavorable geological conditions and improper management had much higher leakage values. The standard deviation of leakage at the water outlets was the next lowest. The role of different processes and running states had the greatest role in CH4 leakage. The leakage from horizontal wellheads was the highest, with an average rate of 20.80 l/min, compared to the average of leakage from flowing wells at 0.88 l/min; this is far below that of the wells that used mechanical gas pumping. T he overall emission factor of the 113 examined wells was 176 kg CO2-e t-1, which was far greater than the previously reported Australian emission level (11.7 kg CO2-e t-1).