Experimental and numerical investigations on spilled oil migration and contamination characteristics in freezing soils

• The migration and contamination process of oil spill in cold regions was investigated. • A mathematical model was developed to describe the oil migration process by considering ice-water phase change. • Total oil mass infiltrating the soil increased by 142 % when cold end temperature boundary increased from −5 °C to −1 °C. • 33 % increase in spilled oil was observed when the initial water content reduced from 20 % to 12 %. Pipeline oil spills can lead to environmental pollution and alter the thermal state of soils in cold regions. This study investigatesd the characteristics of oil migration in freezing soils. A series of laboratory tests were conducted on soils with different temperature boundaries and initial water contents. Using porous media theory, a mathematical model was developed to describe the oil migration process, accounting for the ice-water phase change within soil pores and the influence of soil temperature. The model was validated by comparing simulation results with experimental data. The study revealed that, 1) the temperature of spilled oil significantly disrupts the soil’s thermal state, and the oil migration can be affected by several factors, e.g. the temperature gradient, gravity and concentration gradients within the soil. 2) soil temperature affects oil viscosity and the adsorption of soil particles, influencing the migration rate and diffusion range. The low permeability of frozen soil inhibits oil seepage. When the temperature boundary increases from −5 °C to −1 °C, the total oil infiltrating the soil increases by 142 %.3) Pore water content impedes oil migration due to the incompatibility between oil and water. A 32.5 % increase in spilled oil is observed when the initial water content reduces from 20% to 12%. This study provides a scientific basis for soil restoration following oil pipeline leak in cold regions.