Sensitivity Analysis of Crude Oil and Soil Properties on Diffusion Rate

Crude oil diffusion in soil is influenced by both the physical properties of the crude oil and the characteristics of the receiving soil. This study investigated the sensitivity of crude oil diffusion to API gravity and soil porosity using a numerical sensitivity-analysis approach. API gravity was varied from heavy to light crude-oil conditions, while soil porosity was varied from 0.25 to 0.55 to represent conditions ranging from relatively low- to high-porosity soils. The effect of each parameter on crude-oil concentration distribution was evaluated in the lateral and longitudinal directions after a simulation period of 35 days. The results showed that increasing API gravity resulted in a gradual reduction in localized crude-oil concentration. In the lateral direction, concentration decreased from approximately 3.54×10^4ppm at 10° API to 3.25×10^4ppm at 50° API, while the longitudinal concentration decreased from 4.28×10^4to 4.07×10^4ppm. In contrast, increasing soil porosity from 0.25 to 0.55 increased concentration from approximately 2.98×10^4to 3.34×10^4ppm in the lateral direction and from 3.91×10^4to 4.13×10^4ppm in the longitudinal direction. The response to porosity was more pronounced than the response to API gravity, indicating that soil pore structure exerts a stronger influence on simulated crude-oil diffusion under the investigated conditions. Concentrations were consistently higher in the longitudinal direction than in the lateral direction, indicating directional differences in diffusion behaviour. The findings demonstrate that both crude-oil characteristics and soil properties influence diffusion, with soil porosity exhibiting greater sensitivity within the investigated parameter ranges.