Old goaf coalbed methane extracting and mining system and method

Abstract

The invention discloses an old goaf coalbed methane extracting and mining system and method. The method includes the following steps that: an extracting and mining borehole is constructed in a coal pillar between adjacent old goaf cavities, and an extracting and mining pipe and a grouting pipe are arranged in the extracting and mining borehole sequentially; a valve III is opened, cement mortar is injected, so that the cement mortar and the coal pillar can form a closed space, and a valve I is opened, and N2 which is pressurized by a gas booster pump is injected into a gas injection pipe from a ground N2 storage tank, and the coal pillar is fractured; a valve II is opened, and coalbed methane is extracted and mined by a ground extracting and mining station and through an extracting and mining pipe, and initial gas flow rate is recorded as A; when coalbed methane flow rate is decreased to 30% of the initial gas flow rate A, coal-bed methane displacement with N2 is repeated until the coalbed methane flow rate is decreased to 16% of the initial gas flow rate A, and the valve II is closed, and coalbed methane extracting and mining is stopped. With the method adopted, the quantity of extracted and mined coalbed methane can be increased, and the service life of a singe surface borehole can be prolonged.

Description

technical field [0001] The invention relates to a system and method for extracting coalbed methane in an old goaf, and belongs to the technical field of extracting coalbed methane. Background technique [0002] At present, my country mainly adopts surface drilling to extract residual coalbed methane in the old empty area, and the extraction effect is not ideal. When the production of coalbed methane decreases, surface drilling is often abandoned directly. A large amount of underground coalbed methane is fully extracted and utilized, and a large amount of available coalbed methane is still adsorbed in a large amount of unmined coal in the underground. It will take a certain time for this part of coalbed methane to desorb from the adsorption state to the free state. At this time, if the ground drilling is abandoned, a large amount of coalbed methane will be abandoned. The utilization of ground still requires ground purification, which undoubtedly increases the cost. [0003] ...

AI Technical Summary

Problems solved by technology

At present, the gas in the old goaf is mainly drilled from the ground to the upper fissure zone of the goaf to extract the gas in the old goaf. This method is difficult to construct during the drilling construction process, with high accident rates, low porosity, and low output. Small size, high cost, and can only extract gas from a single old empty area

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