Liquid nitrogen freeze-thaw cracking method for improving permeability of low-permeability coal seams

Abstract

The liquid nitrogen freeze-thaw cracking anti-permeability method for low-permeability coal seams comprises the following steps: a) drilling a freeze-thaw borehole and a monitoring borehole; The nitrogen separation device is connected, and the nitrogen separation device is connected to the liquid nitrogen injection pump; c) Install a temperature monitoring device in the monitoring borehole, and after the temperature monitored by the temperature monitoring device is stable, confirm that it is the initial temperature T0 at this time; d) Start Inject liquid nitrogen pump, drive the nitrogen separation device to inject liquid nitrogen into the freeze-thaw borehole, and monitor the borehole temperature in real time; e) When the temperature T in the monitored borehole is 50%-80% lower than T0, stop injecting Liquid nitrogen, and continue to monitor the temperature in the borehole; f) when the temperature T in the monitored borehole rises to |T-T0| / T0<5%, repeat steps d) and e); g) repeat step f) 3 -5 times. The invention transforms the pore structure of the original coal body, effectively solves the problem of poor permeability enhancement effect of the low-permeability coal seam, and greatly improves the permeability of the low-permeability coal seam.

Description

technical field [0001] The invention relates to a coal seam permeability enhancement method, in particular to a low permeability coal seam liquid nitrogen freeze-thaw cracking enhancement method. Background technique [0002] Draining coalbed methane can not only develop and utilize coalbed methane resources, but more importantly, it can guarantee the production safety of coalbed mining. However, due to the insufficient development of coal seam cracks and bedding in low-permeability coal seams, the permeability of coal bed methane is extremely low, which is not only unfavorable to the development and utilization of coal bed methane, but also unfavorable to the production safety of coal seam mining. How to exploit low-permeability coal seam coalbed methane efficiently has become a technical topic of widespread concern to domestic and foreign researchers and engineers, and many scientific research results have been obtained. [0003] At present, the method to increase the rec...

AI Technical Summary

Problems solved by technology

Among them, the hydraulic anti-reflection technology has the advantages of simple process operation and low technical cost, but it usually requires the conditions to protect the coal and rock pillars on site, and it is easy to induce injection holes to cause the gas in the roadway to exceed the limit, which affects the safety of construction operations

Due to the complex technical process and high technical cost of high-energy gas permeability enhancement, it is difficult to feed and lower the tube during the construction of low-permeability broken soft coal seams, and due to the anisotropy of the coal body and the limitation of the amount of charge, the blasting range is small and cracks Expansion directionality is poor. At the same time, due to the existence of gas in the coal seam, the risk of gas explosion and outburst in the hole is increased during the blasting process. Therefore, the application of this anti-reflection technology is severely limited

Directional long-hole drilling technology has the advantages of large drilling length and directional drilling, but it is difficult to take advantage of the drainage effect in low-permeability broken soft coal seams

[0004] As coal enters deep mining, the characteristics of high stress, high gas and low permeability of coal seams become more and more significant, and the existing anti-reflection technology of coal seams is increasingly unable to meet the safety production requirements of mines

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