Evaluation of Drainage Performance of High-gas Tunnel in Chengdu Plain Shallow Natural Gas Area

Abstract:

Aiming at the difficulty of shield construction of high-gas tunnel in the shallow natural gas work area， with the help of engineering examples， the influencing factors of drainage performance of shallow natural gas in Chengdu Plain were analyzed by using theoretical analysis， numerical simulation and field test， and the effective radius and drainage time in the study area were determined. The results show that when the fracture permeability is 39 mD and the gas pressure is 0.31 MPa， the effective pumping radius of high-gas area of shallow natural gas in the study area is 5 m， and the pumping time is 60 min， which is greatly different from the coal seam gas. The negative pressure of pumping has a great effect on the discharge， but a little effect on the effective pumping radius. The discharge and effective pumping radius are positively correlated with the change of initial permeability of formation.

Key words:gas tunnel;gas drainage;numerical simulation;field test;sandstone stratum