Research progress on characteristics of leakage and diffusion of buried CO₂ pipeline

Objective CO₂ pipeline transmission, a key link in the industrial chain of carbon capture, utilization, and storage (CCUS) technology, is exposed to risks of accidental leakage during operation. Compared with aboveground pipelines, buried high-pressure pipelines follow the leakage and diffusion mechanism subject to more intricate impacts from soil resistance. Unfortunately, existing researches center on reviewing the leakage and diffusion characteristics of aboveground CO₂ pipelines, neglecting the specific challenges faced by buried ones.

Methods This study focused on two common scenarios involving buried pipelines: small hole leakage and full-scale fracture. The experimental and simulation research progress on leakage and diffusion of buried pipelines was reviewed and evaluated through literature research. The influences of soil geological conditions, soil temperatures, ambient pressures, and wind velocities on the CO₂ seepage and diffusion processes in the soil were also examined. Furthermore, the study summarized the currently prevalent modeling methods and physical models utilized for exploring leakage and diffusion of buried CO₂ pipelines with full-scale fractures.

Results The soil temperature changes near leakage openings and the growth patterns of dry ice layers and frozen soil layers were studied mainly through mini experiments, to reveal the characteristics of near-field leakage sources in the small hole leakage scenario of buried CO₂ pipelines. The simulation study of far-field diffusion characteristics in the same scenario was mostly based on the assumption of constant soil porosity, neglecting the effects of phase transition of fluid and shock pressure on soil porosity. The gas jet diffusion of buried pipelines in the full-scale fracture scenario was studied mainly through simulations, and most models were directly derived from the physical prototype of formed pits, without considering the effects of pit formation on gas jet diffusion.

Conclusion There remains considerable room for advancement in conducting field tests for full-scale fractures of buried CO₂ pipelines and developing theoretical models for small hole leakage and diffusion scenarios. It is recommended to conduct specialized research on the diffusion mechanism of CO₂ in soil, emphasizing geological conditions and ambient environmental factors. Furthermore, efforts should be intensified in conducting leakage and diffusion experiments for buried CO₂ pipelines with large diameters or full-scale fractures, aiming to acquire more experimental data essential for constructing comprehensive and precise mathematical and physical models.