Numerical Investigation of Methane Transport Within and Around Evolving Cracks

ABSTRACT

Urban natural gas is transported through buried pipelines that are exposed to water, chemical and electrochemical corrosion, making the pipe walls vulnerable to perforation and subsequent gas leakage. The deformation behavior of soil during leakage limits the accurate prediction of methane diffusion by numerical simulation, and is influenced by diffusion coefficient, leakage velocity, and soil characteristics. Therefore, a Darcy–Brinkman–Stokes–Diffusion model was developed using OpenFOAM and validated to describe the evolution of soil fracture morphology and gas diffusion behavior during gas leakage. Simulation and experimental results show that three main cracks with small cavities inside were formed when the injection velocity exceeded approximately 0.2 m/s. Under low injection conditions, soil deformation was negligible, but the velocity exhibited a significant non‐uniform distribution. As leakage velocity increases, soil fractures widen, although crack orientation remains largely unchanged. Meanwhile, methane transport shifts from uniform diffusion to crack‐guided directional flow. When the diffusion coefficient exceeds approximately 2 × 10 ⁻⁴ m ² /s, the gas transitions from diffusing primarily along the sides of the crack to diffusing uniformly throughout it. In soils containing natural cracks, gas leakage induces new fractures that intersect existing ones, reshaping the crack network and enhancing methane migration. These results provide a novel predictive numerical model and new insights into natural gas leakage in soil.