Measuring changes in background dissolved gases to evaluate multi-component gas dissolution: Laboratory experiments and implications for stray gas monitoring

Abstract

Gas emitted from leaking wells is a concern for natural gas production as well as the underground storage of carbon dioxide and hydrogen. Stray gas migration through heterogeneous layers, and its subsequent dissolution, controls the fraction emitted to the atmosphere rather than dissolved in groundwater. Understanding the effects of multiple gas components on gas dissolution is important for risk prediction, and measuring changes in background dissolved gas concentrations may provide a complementary tool to support site investigation. A series of two-dimensional laboratory experiments were performed to measure transient gas saturations and background dissolved gas concentrations during and after gas injection into heterogeneous sand packs. Mass transfer was influenced by both source architecture and groundwater velocity, and steady-state modelling was used to estimate mass transfer coefficients at the scale of the flow cell. The results demonstrate the potential of using background dissolved gases as part of gas migration monitoring strategies.