Objective Carbon Capture, Utilization, and Storage (CCUS) is a critical technical pathway for large-scale carbon emission reduction, yet pipeline leakage remains a key constraint on its operational safety. Unlike aboveground pipelines, buried pipelines exhibit more complex leakage diffusion dynamics due to interactions with surrounding soil. Additionally, the Joule–Thomson effect during supercritical CO₂ leakage causes rapid soil cooling, triggering secondary risks such as pipeline embrittlement and frost heave.

Methods This study aims to reveal how soil water content, leakage direction, and leakage orifice nominal diameter affect the leakage-diffusion behavior of buried CO2 pipelines and the evolution of the soil temperature field. To this end, eleven test runs were conducted on an industrial-scale test platform for buried CO2 pipeline leakage. The soil temperature field is dynamically monitored throughout the test, while the surface CO₂ jet morphology and frozen soil zone parameters are recorded simultaneously.

Results Soil water content correlates positively with the diffusion range of the low-temperature soil zone. The evolution curve of the maximum radial extension distance of the low-temperature zone over time generally follows an S-shaped growth pattern. Under high soil water content, the morphological asymmetry of the frozen soil zone around the pipeline increases significantly. Leakage direction determines the preferential diffusion path of low-temperature CO₂ jets in soil, and the peak temperature drop azimuth in the circumferential soil temperature field aligns with the initial jet direction. The nominal diameter of the leakage orifice correlates negatively with the magnitude of soil temperature drop.

Conclusion These findings clarify how soil water content, leakage direction, and leakage orifice nominal diameter influence soil temperature field evolution following supercritical CO₂ pipeline leaks. They provide experimental basis and theoretical support for optimizing leakage monitoring point placement, assessing low-temperature risks, and formulating emergency response strategies for long-distance CO₂ pipelines.