Dual Control of Permeability-Viscosity in Coalbed CO2 Flow: Carbon Safety Supervision Assessment for Optimized Sequestration

Geological sequestration of CO₂ in coal seams is one of the effective methods to reduce carbon emissions. However, the combined effects of evolving CO₂ viscosity and the inherently low permeability of coal reservoirs can significantly inhibit CO₂ flow capacity, thereby affecting the overall storage efficiency. The dynamic dual-control mechanisms governing CO₂ migration in coal seams remain insufficiently understood. The analysis of dynamic dual-control weights influencing CO₂ flow behavior is focused on in this study. On this basis, a mathematical model is developed and numerical simulations are conducted. The model captures the transient evolution of CO₂ viscosity and the permeability of coal seams during the sequestration process and investigates the coupling relationship between CO₂ properties and coal seam permeability. Two mathematical decomposition methods─the logarithmic decomposition method and the finite difference decomposition method─are employed to perform parameter decoupling analysis of CO₂ migration in coal seams. The dynamic coupling characteristics between permeability and viscosity are elucidated, and the dominant influence weights of their evolution on the CO₂ flow field are quantitatively evaluated. The study clarifies the stage-dependent control of fluid migration: permeability dominates initially, viscosity gains influence midstage, and both reach dynamic equilibrium over time. A dynamic dual-control weighting approach is proposed to optimize injection strategies, aiming to enhance CO₂ mobility and storage efficiency in an economically viable manner. The findings provide a theoretical basis for the accurate performance assessment of CO₂ sequestration in coal seams.