Experimental study on the diagnosis of operation state of gas extraction pipeline based on pressure gradient method

The working state of the gas drainage pipe network is the key to the safe drainage of underground mine gas. In order to quickly and accurately determine whether the pipe network is working normally, the flow law of the gas in the pipeline is studied. A diagnosis method of gas extraction pipeline by pressure gradient method is established. A gas drainage pipe network experimental platform is constructed. And the blockage and leakage of single pipe are carried out. The influence of air leakage of main pipe on negative pressure of branch pipe is studied, as well as the influence of negative pressure change of temporary pumping station on parallel pipe is explored. The method of image photography is proposed to calculate the pipeline flow, and the error is 2.7% compared with the orifice flowmeter. The results show that when the abnormalities exist in the extraction pipeline, the slope of the pressure curve corresponding to the abnormalities increases rapidly, the slope of the downstream curve is slightly larger than the slope of the upstream curve when the pipeline is leaking, and the slope of the downstream curve returns to the same as the slope of the upstream curve when the pipeline is blocked. The closer the location of the vacuum pump is to the air leakage, the faster the negative pressure of the vacuum pump decreases, and the less it affects the negative pressure of the branch circuit. When the downhole temporary pumping station extraction system is connected in series with the permanent pumping station extraction system on the ground, the temporary pumping station’s negative pressure value needs to be set reasonably, seriously affecting the extraction effect of the adjacent extraction pipeline. Finally, monitoring the gas drainage pipeline in Yuwu mine by pressure gradient method, it is found that the pressure drop slope at measuring points 6–7 is abnormal (−3 × 104), and the pressure drop slope of measuring points 7–8 returned to normal (−7 × 105), so it is judged that the drainage pipeline is blocked at 1300–1500 m away from the pump station.