Heterogeneous Wettability Alters Methane Migration and Leakage in Shallow Aquifers

TL;DR

This study demonstrates how heterogeneity in wettability, influenced by mineralogy and salinity, impacts methane migration and leakage in aquifers, improving risk assessment models for subsurface gas storage and emissions.

Contribution

It introduces a cross-scale framework linking molecular wettability variations to continuum flow simulations, enhancing understanding of methane behavior in aquifers.

Findings

Methane trapping decreases by up to 10% due to wettability heterogeneity.

Methane leakage to the atmosphere can increase by up to 20%.

Wettability effects depend on permeability, salinity, and facies proportions.

Abstract

Capillary heterogeneity is increasingly recognized as a first-order control on gas plume migration and trapping in aquifers and storage formations. We show that spatial variability in the water-methane contact angle, determined by mineralogy and salinity, alters capillary entry pressures and migration pathways. Using molecular dynamics simulations, we estimate contact angles on quartz and kaolinite under fresh and saline conditions and incorporate these results into continuum-scale multiphase flow simulations via a contact-angle-informed Leverett J function, mapping wettability directly onto continuum-scale flow properties. Accounting for contact angle heterogeneity affects methane behavior: mobile and residually trapped methane in aquifers decrease by up to 10 percent, while leakage to the atmosphere increases by as much as 20 percent. The magnitude of this effect depends on permeability contrast, leakage rate, salinity, and facies proportions. By coupling molecular-scale wettability to continuum-scale flow and transport, this cross-scale framework provides a physically grounded basis for groundwater protection and risk assessment and yields more reliable emissions estimates. The approach can be generalized to other subsurface gas transport problems, including hydrogen and carbon dioxide storage, as well as natural releases such as methane from permafrost thaw.