Method for improving methane recovery by self-improvement of coal seam induced by nitrogen injection

Abstract

The invention discloses a method for improving the methane recovery efficiency by self-transformation of a coal seam induced by nitrogen injection. When methane is extracted from the coal seam, a production casing is lowered to the middle of the coal seam, and a nitrogen injection pipeline connected to a nitrogen source is arranged beside the production casing; a packer is further arranged, and the packer separates the top of the coal seam from a casing annulus below; perforating is performed at the top of the coal seam and the bottom of the coal seam; and a nitrogen injection valve on the nitrogen injection pipeline is opened, nitrogen is injected into the space above the packer through the nitrogen injection pipeline, and formation water in a coal-rock reservoir flows through the coal seam under the displacement of the injected nitrogen and then enters the bottom of a well through perforations at the bottom of the casing to drain water and reduce pressure. The nitrogen injected intothe coal-rock reservoir accelerates the drainage of the formation water, also reduces the partial pressure of the methane in the coal seam at the same time, and accelerates desorption of the methane which exists in the coal seam in an adsorptive state, coal matrix shrinkage is caused after the desorption of the methane, and the coal matrix shrinkage and release of the coal seam stress create new cracks so that the permeability of the coal seam is improved.

Description

technical field [0001] The invention belongs to the technical field of coal bed methane exploitation, and relates to a method for improving the recovery rate of coal bed methane by inducing the self-improvement of the coal bed by injecting nitrogen. Background technique [0002] In recent years, with the adjustment of the global energy structure, the exploitation of unconventional resources has gradually increased. As an important unconventional energy source, coalbed methane is of strategic significance for its economical and efficient exploitation. 90% of coalbed methane exists in the form of adsorbed gas. Therefore, the basis for the successful development of coalbed methane is the exploitation of adsorbed gas in coal seams. [0003] At present, there are mainly two methods of mining coalbed methane: ① Drainage and depressurization method. Drainage reduces the pressure of the coal seam and promotes the desorption of methane in the coal seam. This method is simple and pr...

AI Technical Summary

Problems solved by technology

This injection method not only requires a large amount of non-hydrocarbon gas, but also contains a large amount of water in the coal reservoir, which makes gas injection difficult, and it is difficult to ensure a sufficient volume of gas injected into the coal seam, and the ultimate effect of enhancing the recovery rate is limited.

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