Estimating Natural Gas Emissions from Underground Pipelines using Surface Concentration Measurements

Abstract:

Natural gas from leaking underground pipelines result in environmental, health, and safety hazards. Early determination of leakage rates from underground leaks is necessary to identify potentially dangerous leaks early, and to reduce environmental impact over time. However, quantitative estimation of underground leakage rates remains challenging, considering the complex nature of the gas transport processes in the shallow subsurface. We present a novel method to estimate leak rates developed from controlled underground natural gas release experiments at field scale. Experiments provided data to evaluate the relationship between the underground leakage rate and surface methane concentration data in varying soil and pipeline conditions, allowing the development of a dimensionless concentration number which considers soil and fluid characteristics and is correlated to leakage rate. Peak surface methane concentrations increased with leakage rate, while surface concentrations decreased exponentially with distance from the source. Deviations between the estimated and actual leakage rates ranged from 9% to 33%. These findings show that the proposed leak rate estimation method may be useful for prioritizing leak repair, while warranting broader field-scale method validation studies. The method could be applied across a range of soil and surface covering conditions.