Mixed gas displacement method for coalbed methane in horizontal well

Abstract

The invention discloses a method for displacing coal bed gas with mixed gas in a horizontal well, and relates to a coal bed gas mining method. The present invention comprises the following steps: 1. form some horizontal wells (10) in the coal seam (30) by horizontal well technology, and some horizontal wells (10) are arranged alternately and at intervals with the same structure injection wells (11) and recovery wells (12 ) composition; ② using high-pressure injection equipment to inject the mixed gas through the injection well (11) into the coal seam (30) containing coalbed methane; ③ obtaining the mixed gas containing coalbed methane in the recovery well (12) until the obtained methane concentration It is lower than the economic mining concentration and the safe concentration. The present invention takes into account the advantages of strong displacement gas competitive adsorption and the effect of increasing permeability of weak displacement gas and reducing the partial pressure of methane gas; improves the recovery rate and unit output of coalbed methane, reduces the cost of coalbed methane mining, and can carry out waste gas geology at the same time Sequestration, large-scale emission reduction and sequestration of waste gases.

Description

technical field [0001] The invention relates to a method for mining coal bed gas, in particular to a method for displacing coal bed gas with mixed gas in a horizontal well. Background technique [0002] Most coal seams in my country have relatively high gas content, with an average gas content of 10m 3 Mining areas above / t account for 41%; but the permeability of coal seams is low, generally 0.002-16.17mD (milli-Darcy). Among them, those with permeability less than 1.0mD account for 72%, which is very unfavorable to the exploitation and utilization of coalbed methane. my country's coal seams generally have low permeability and slow desorption speed, which lead to low production and fast attenuation of most coal seam test wells, and it is difficult to form a stable industrial gas flow. [0003] The current CBM mining methods with relatively mature technology include: surface vertical wells, ground mining area wells (Gobwell), underground horizontal holes (that is, undergro...

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Problems solved by technology

like figure 1 , when the recovery well (22) is arranged at four points in the traditional vertical well displacement method, there is a displacement dead zone (40), and this part of the coalbed methane cannot be recovered or fully recovered, which reduces the recovery rate of the coalbed methane; and A large part of the vertical well is in other rock formations (non-coal seams), and a very small part is in the coal seam, which takes up a lot of money

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