Testing Lagrangian atmospheric dispersion modelling to monitor CO_2 and CH_4 leakage from geosequestration

摘要

We assess the performance of an inverse Lagrangian dispersion technique for its suitability to quantify leakages from geological storage of CO_2. We find the technique is accurate ((Q_(bLS)/Q) = 0.99, σ = 0.29) when strict meteorological filtering is applied to ensure that Monin-Obukhov Similarity Theory is valid for the periods analysed and when downwind enrichments in tracer gas concentration are 1% or more above background concentration. Because of their respective baseline atmospheric concentrations, this enrichment criterion is less onerous for CH_4 than for CO_2. Therefore for geologically sequestered gas reservoirs with a significant CH_4 component, monitoring CH_4 as a surrogate for CO_2 leakage could be as much as 10 times more sensitive than monitoring CO_2 alone. Additional recommendations for designing a robust atmospheric monitoring strategy for geosequestration include: continuous concentration data; exact inter-calibration of up- and downwind concentration measurements; use of an array of point concentration sensors to maximise the use of spatial information about the leakage plume; and precise isotope ratio measurement to confirm the source of any concentration elevations detected.