Objective As a crucial component of the global energy supply system, natural gas has seen increased utilization in the ongoing transition to clean energy. However, the increasing number of installed pipelines and their extended service durations have raised safety concerns regarding pipeline leaks. Accidents involving natural gas leaks can lead to severe fires and explosions, posing direct threats to the lives and property of nearby residents. Therefore, there is an urgent need for an effective method for scenario construction and concentration field prediction to enhance emergency response capabilities related to natural gas pipeline leaks.

Methods A real-scenario drill platform was developed for high-pressure and large-diameter natural gas pipeline leakage, based on the pipeline fracture control test field. This platform was designed to simulate complex leakage scenarios involving a burial depth of at least 1.5 meters, a pipe diameter larger than or equal to 1,219 mm, and a pressure-bearing capacity of no less than 14 MPa. It is equipped with a rupture disk device that enables dynamic regulation of leakage parameters, including size and direction. Utilizing real-scenario data obtained from the platform, a three-dimensional computational fluid dynamics (CFD) model for pipeline leaks was established in conjunction with the Brinkman equation to accurately reproduce the diffusion patterns of gas leaks from buried pipelines. Building on this model, a 3D concentration field decoupling method based on the algebraic iterative reconstruction technique was proposed. Mapping relations were established between two-dimensional monitoring data and three-dimensional spatial distribution to support field reconstruction, thereby enhancing the generalization ability that is often limited in traditional models.

Results Natural gas diffusion in typical leakage scenarios of buried pipelines was accurately reproduced, exhibiting an elliptical shape in the soil domain and a conical shape in the air domain. The Ground Danger Range (GDR) exceeded 2.5 meters in various leak scenarios, with vertically upward leaks shown to be the most significant factor in expanding the GDR. During the initial leakage phase (before 3,600 seconds), simulations indicated that gas primarily diffused horizontally (horizontal diffusion ＞ downward diffusion), driven by the momentum of the high-speed jet. After this initial period (beyond 3,600 seconds), as gravitational effects intensified, simulations revealed a gradual shift in the dominant diffusion to downward movement. These transitions demonstrate a nonlinear relationship between leak directions and diffusion time points. Because the gas jet direction aligns with the buoyancy direction in a steady-state diffusion scenario, a synergistic acceleration effect occurs. Consequently, it was deduced that the volume of natural gas diffusing from the vertically upward leak opening to the ground was 300 m³, significantly higher than that yielded in the other two directions. This finding further underscores the dominant influence of leak directions on diffusion behavior. The maximum diameter difference between gas clouds from simulations and the decoupling approach was 13.54％, while the height difference of these gas clouds was 11.83％. Additionally, the maximum concentration difference at monitoring points was 14.92％, with a minimum of 6.49％, both meeting the emergency response requirement of at most 20％. These results demonstrate significant improvements in the decoupling accuracy of three-dimensional concentration fields.

Conclusion The integration of the real-scenario platform and the decoupling algorithm offers a solution for scenario construction and 3D concentration field reconstruction with accuracy enhancement for high-pressure and large-diameter pipeline leakage. This combined approach provides key data support for planning machine routes and selecting excavation methods in emergency responses to leaks, significantly improving the reliability of leakage simulations and the rationality of emergency decision-making. The findings of this study offer crucial technical support for safe operations, risk prevention and control, as well as emergency responses within the long-distance natural gas pipeline sector in China.