Capillary Heterogeneity Linked to Methane Lateral Migration in Shallow Unconfined Aquifers
Reza Ershadnia, Corey D. Wallace, Seyyed A. Hosseini, Zhenxue Dai, Mohamad Reza Soltanian
Abstract
Abstract We investigate mechanisms that enhance lateral methane (CH 4 ) plume migration in shallow aquifers that exhibit complex and multiscale sedimentary architecture. We show how heterogeneity in capillary pressure characteristics related to the sedimentary architecture causes gaseous CH 4 to spread over larger areas by retarding, deviating, or blocking upward buoyancy‐driven CH 4 migration. Simplifying or ignoring capillary pressure heterogeneity thus leads to overestimation of leaked CH 4 to the atmosphere, and underestimation of mobile gaseous CH 4 in aquifer. We show, both qualitatively and quantitatively, that meter‐scale sedimentary stratification contributes more to CH 4 plume migration than the millimeter‐ and centimeter‐scale strata comprising them. Results indicate that the extent of gaseous CH 4 leakage, and its associated impacts on groundwater quality and global warming, cannot be accurately assessed unless the sedimentary architecture and resulting heterogeneity in capillary pressure are represented.