Migration of Dissolved Petroleum Components in Finite Frozen Porous Media: Coupling Effects of Geometry and Injection Volume

As global warming and oil and gas development in cold regions increase, oil spills pose a serious threat to fragile polar and high-latitude environments. Dissolved oil components can migrate over long periods through unfrozen water films and micro-pore networks in permafrost. This process presents persistent risks to pore water and hydraulically connected groundwater systems. However, most thermo-hydraulic-chemical (THC) coupled models assume infinite domains, limiting their ability to represent the geometric constraints imposed by frozen fractures and ice lenses in finite domains. In this study, a simplified THC model for frozen porous media was used to isolate and quantify the joint effects of lateral geometric constraints (H) and cumulative injection quantity (Q) on underground contaminant migration. A response surface method (RSM) was used to analyze the nonlinear coupling relationship between these two factors. The results show that lateral geometric constraints are the main factor controlling the contaminant plume morphology. It regulates the transition from confined quasi-two-dimensional vertical migration to three-dimensional lateral diffusion, while cumulative injection quantity mainly controls the overall extent of plume development. And, a significant negative coupling effect between H and Q was found: under strong geometric constraints, lateral dilution is suppressed, causing the plume to unexpectedly penetrate deeper even with relatively low injection amounts. These findings demonstrate the significance of limited-domain constraints within finite-domain soil–groundwater systems in controlling pollutant migration in permafrost environments. They indicate that risk assessments based solely on leakage amounts may underestimate the extent of groundwater pollution under structural constraints.