Electro‐Thermal Subsurface Gas Generation and Transport: Model Validation and Implications

• Published in: Water resources research 2019-06, Vol.55 (6), p.4630-4647
• Main Authors: Molnar, Ian L., Mumford, Kevin G., Krol, Magdalena M.
• Format: Article
• Language: English
• Subjects: Algorithms; Boiling; Carbon dioxide; Carbon sequestration; Cold water; Collapse; Computer simulation; Condensation; Continuum modeling; Dissolved gases; Electrical resistance; Gas flow; Gases; Heat; Heating; invasion percolation; Latent heat; Marine sediments; Marine technology; Mass transport; Multiphase flow; Parameter sensitivity; Peat; Percolation; Plateaus; Resistance heating; Saturation; Sediments; Sensitivity analysis; Soil; Soil contamination; steam; Steam generation; Temperature distribution; thermal remediation; Transport; validation; Water temperature
• ISSN: 0043-1397; 1944-7973
• DOI: 10.1029/2018WR024095

Gas generation and flow in soil is relevant to applications such as the fate of leaking geologically sequestered carbon dioxide, natural releases of methane from peat and marine sediments, and numerous electro‐thermal remediation technologies for contaminated sites, such as electrical resistance heating. While traditional multiphase flow models generally perform poorly in describing unstable gas flow phenomena in soil, Macroscopic Invasion Percolation (MIP) models can reproduce key features of its behavior. When coupled with continuum heat and mass transport models, MIP has the potential to simulate complex subsurface scenarios. However, coupled MIP‐continuum models have not yet been validated against experimental data and lack key mechanisms required for electro‐thermal scenarios. Therefore, the purpose of this study was to (a) incorporate mechanisms required for steam generation and flow into an existing MIP‐continuum model (ET‐MIP), (b) validate ET‐MIP against an experimental lab‐scale electrical resistance heating study, and (c) investigate the sensitivity of water boiling and gas (steam) transport to key parameters. Water boiling plateaus (i.e., latent heat), heat recirculation within steam clusters, and steam collapse (i.e., condensation) mechanisms were added to ET‐MIP. ET‐MIP closely matched observed transient gas saturation distributions, measurements of electrical current, and temperature distributions. Heat recirculation and cluster collapse were identified as the key mechanisms required to describe gas flow dynamics using a MIP algorithm. Sensitivity analysis revealed that gas generation rates and transport distances, particularly through regions of cold water, are sensitive to the presence of dissolved gases. Key Points Coupled Macroscopic Invasion Percolation (MIP) model with continuum heat and mass models accurately reproduced lab‐scale gas production and migration Simulation of condensation mechanisms and heat recirculation within gas clusters were key to capturing gas flow dynamics with MIP Higher concentrations of dissolved oxygen and nitrogen increased gas mobilization and decreased steam condensation rates in cold water