Study on time series rule of buried pipe failure under high-intensity coal mining in a gas-coal overlapping area

Abstract

The high-intensity mining of coal face in the Ordos gas-coal overlapping area can easily lead to the failure of shallowly buried oil & gas pipelines. It is of great significance to clarify the time series of the pipeline failure during the advancing process of the panel in this area for the accurate maintenance and parameter optimization of the gathering and transmission pipelines. Firstly, the theoretical algorithm of volume strain (VS) is proposed through theoretical analysis. Then, a new method for failure damage discrimination in the tensile and compressive states locally is respectively constructed by the volume strain limit. Next, the deformation and volumetric strain of the pipeline in the axial and circumferential directions were analyzed by numerical simulation, and the time series law of buried pipeline damage was clarified. At the same time, the numerical results are compared and analyzed with the monitoring data and theoretical results to verify the reasonableness and accuracy of the experimental results. The results show that the volumetric strain limits in tension and compression are, for example, 0.42% and −0.31% for a 508 mm diameter gas transmission pipe. The deformation of the pipeline is smaller than that of the overburden during the process of panel advancing, and the deformation between them is non-synergistic. The closer the panel is to the pipeline, the greater the degree of non-synergistic. In the axial direction, the deformation curves of the tubes are funnel-shaped. The ellipticity of the tube decreases as the distance between the tube and the panel decreases, and the mathematical relationship between them can be expressed as an exponential function. The volume strain between the inflection points of the pipeline is always less than 0, and the VS from the inflection point to the end is always greater than 0. Furthermore, the volume strain of the pipe is symmetrical to the left and right about the position of the center of the subsidence. The volume strain distribution at the bottom and top of the pipe is not symmetrical, and the absolute value of the volume strain at the top is always greater than that at the bottom at the same axial position. The failure profiles at the top and bottom of the pipeline are shown as “∩” and “∪”, and at the same axial position show “S”. The location and pattern of axial damage of the pipeline: compression damage at the bottom center, and tensile damage at the bottom two ends. The panel is gradually approaching the pipeline process, the failure from the center to the inflection point and from the end to the inflection point of the pipeline is successively generated, and the center is earlier than that at both ends, and the top is earlier than the bottom. At the same time, the failure of the pipeline ring is the transfer from 270° to 180°, where 330°-150° is the most vulnerable to damage orientation, and the minimum deformation is the transfer from 120° to 0°. Finally, the reliability of the results was verified by the deformation, the ellipticity, the shear stress of the pipe, and the ground settlement. The research results further clarify the orientation and time series rule of pipeline failure, which is conducive to the precise maintenance and efficient construction of pipeline projects and provides a reference for promoting the coordinated mining of oil-gas-coal resources.

Keywords

• high-intensity coal mining
• gas-coal overlapping area
• shallow buried pipeline
• failure orientation
• volume strain limit
• time series rule