Xingyu Wang

Accurate prediction of natural gas dispersion from buried pipelines is critical for risk assessment and emergency response. However, conventional numerical simulations often simplify soil as a homogeneous isotropic porous medium, which deviates significantly from real-world conditions characterized by stratification, anisotropy, and spatial heterogeneity. This study systematically investigates the effects of these non-ideal soil characteristics on methane diffusion behavior using computational fluid dynamics (CFD). Four distinct soil models—a baseline homogeneous model, a layered model, an anisotropic model, and a spatially heterogeneous model—were constructed and compared under identical leakage scenarios. Key risk indicators, including First Danger Time (FDT), Farthest Danger Range (FDR), Ground Danger Range (GDR), and leakage mass flow rate, were quantitatively evaluated. Results indicate that soil layering enhances vertical migration and expands horizontal hazard ranges, reducing FDT by approximately 8%. Anisotropy introduces a pronounced directional dependence in gas migration, with horizontal-preferred permeability leading to severe underestimation of lateral risk by homogeneous assumptions. The spatially heterogeneous model exhibits reduced hazard ranges compared to the homogeneous case but accelerates early breakthrough. Comprehensive evaluation reveals that the homogeneous model systematically underestimates lateral diffusion distances and delays alarm times. This study provides a quantitative basis for selecting appropriate soil modeling strategies, emphasizing that incorporating soil heterogeneity is essential for reliable safety assessments of buried gas pipelines.

Buried natural gas pipeline leakage poses significant risks to public safety and environmental sustainability. A three-dimensional transient computational fluid dynamics model is established to investigate gas leakage and diffusion behavior, with a focus on quantifying the differences between standalone soil models and soil–atmosphere-coupled models. First danger time (FDT), farthest danger range (FDR), and ground danger range (GDR) are adopted as standardized safety metrics that translate complex concentration fields into actionable emergency response parameters. Simulation results indicate that the coupled model predicts an FDT 4.9% earlier and a GDR 39.7% smaller than the standalone soil model under no-wind conditions, highlighting the necessity of coupling. Increasing temperature reduces leakage mass flow rate by 8.4% but produces only marginal changes in FDT (6.01–6.47 s) and GDR (1.888–1.973 m) across the −10 °C to 40 °C envelope. Wind speed exhibits a non-monotonic, time-dependent effect: the shortest FDT occurs at 5 m/s (5.71 s), while the worst-case spatial hazard occurs at 2 m/s (FDR = 3.423 m at 60 s, 3.304 m at 100 s). A crosswind configuration reduces GDR by merely 1.6% when compared with an along-wind configuration, indicating weak directional sensitivity. Topography dominates hazard onset timing: a canyon shortens FDT to 0.33 s, while a hill delays it to 18.48 s—a 43-fold span. Offset obstacles with upwind configuration maximize FDT delay to 8.07 s (+30.6%) while enabling late-stage wake-driven GDR expansion. These findings provide quantitative guidance for risk assessment, emergency response, and monitoring layout of buried natural gas pipelines.

Understanding the law of gas diffusion in soil is essential for pipeline risk assessment. A 3D CFD model of natural gas leakage and diffusion from buried pipelines was developed in Ansys Fluent using the Detached Eddy Simulation turbulence model, with soil as an isotropic porous medium. Six parameters—burial depth, pipe diameter, transportation pressure, leak hole diameter, hole shape, and hole orientation—were systematically investigated under an identical numerical framework. First Danger Time (FDT), Farthest Danger Range (FDR), and Ground Danger Range (GDR) were used as unified hazard metrics for quantitative cross-factor comparison. As burial depth increases, FDT and FDR increase monotonically, whereas GDR peaks at 2.0 m. Increasing pipe diameter reduces FDT, FDR, and GDR. Higher pipeline pressure shortens FDT and expands FDR and GDR. Leak hole diameter dominates: increasing from 5 to 200 mm reduces FDT to nearly zero. For equal cross-sectional area, rectangular slits yield the highest mass flow rate and largest danger range, while triangular holes produce the shortest FDT owing to strong corner-induced turbulence. Upward leaks give the shortest FDT but smallest FDR; downward leaks produce the largest FDR; side leaks cause the longest FDT but largest GDR. Factor influence ranking by FDT and FDR change is: leak hole diameter, burial depth, pipeline pressure, hole orientation, pipe diameter, and hole shape. These results provide a quantitative framework for hazard assessment, sensor layout optimization, and emergency-response prioritization in buried natural gas pipelines.

This study investigates methane leakage and diffusion from a buried high-pressure natural gas pipeline (8 MPa, 1000 mm diameter) using CFD simulations with the DES turbulence model. Based on homogeneous and layered soil models, the influences of soil porosity (0.46 to 0.54), particle size (10 μm to 100 μm), and soil stratification on the spatial and temporal characteristics of methane diffusion are systematically explored. The simulation results show that (1) methane diffuses from the leak hole to the surrounding soil in an ellipsoidal pattern, with the fastest diffusion speed along the pipeline’s axial direction. (2) In homogeneous soil, within the range of soil parameter values considered in this study, the absolute changes in risk assessment indices (FDR, GDR) caused by soil particle size were more significant; whereas the relative percentage changes in risk assessment indicators caused by soil porosity were more pronounced. (3) In layered soil, the permeability contrast between adjacent layers creates the permeability discontinuity interface effect. When a fine-grained or low-porosity layer overlies a coarse-grained layer, the upper layer acts as a hydraulic barrier, prolonging FDT from 130 s to 354 s while promoting significant horizontal spread at the interface. Conversely, a coarse-grained or high-porosity upper layer accelerates vertical breakthrough. These findings provide a scientific basis for risk assessment, monitoring site optimization, and emergency response planning, particularly in regions with heterogeneous stratified soils.

During shale gas field production, wellhead throttle valves are prone to erosion caused by solid particles carried in the gas stream, posing significant safety risks. Existing studies on erosion primarily focus on simple structure like elbows and tees, while research on gas–solid two-phase flow erosion in needle throttle valves remains limited. This paper establishes a numerical model based on the CFD-DPM approach, integrating actual shale gas field production conditions to investigate the erosion behavior of needle throttle valves under varying openings, particle sizes, inlet velocities, and particle mass flow rates. The results show that the valve spool consistently exhibits the highest erosion rate among all components, with the most severe erosion localized at its front end. At a 1/4 opening, particles colliding with the spool exhibit significantly increased frequency and energy when re-entering the upstream pipeline, raising the risk of blockages. Furthermore, when the opening exceeds 2/4, the valve chamber experiences higher erosion rates than the upstream and downstream pipelines. This study provides critical insights for optimizing valve design and maintenance strategies, thereby enhancing service life and ensuring safe shale gas production.