Intermediate-Scale Laboratory Investigation of Stray Gas Migration Impacts: Transient Gas Flow and Surface Expression

Area of Science:

• Environmental Science
• Geosciences
• Petroleum Engineering

Background:

• Petroleum development is a major source of greenhouse gas emissions.
• Stray gas migration is a potential emission source, but its impact on overall emissions and groundwater is not well understood.
• Quantifying stray gas flow and dissolution is crucial for environmental assessment.

Purpose of the Study:

• To investigate the environmental expression of stray gas migration.
• To quantify gas flow, dissolution, and surface leakage in different geological conditions.
• To understand the relationship between subsurface characteristics and stray gas expression.

Main Methods:

• Utilized an intermediate-scale, two-dimensional flow cell (150 × 150 × 2 cm³).
• Experiment conducted in homogeneous and heterogeneous sand configurations.
• Enabled visualization of gas movement, aqueous sampling, and real-time measurement of surface gas fluxes.

Main Results:

• Gas transport to the surface occurs through discontinuous conduits influenced by geology.
• Surface gas expression does not directly correlate with the magnitude of subsurface leaks.
• 35-39% of methane dissolved into the aqueous phase, while 61-65% escaped to the atmosphere.

Conclusions:

• Subsurface characteristics and gas flow dynamics are primary drivers of stray gas expression in sandy aquifers.
• Geological heterogeneity significantly influences the pathways and rate of stray gas migration.
• Accurate assessment of stray gas requires considering both subsurface flow and surface leakage dynamics.