The invention discloses a
system and a method for increasing drainage quantity of
coal bed gas of a ground
well drainage goaf and belongs to the technical field of
coal bed gas drainage. The method includes: constructing a drainage well between adjacent goaf holes, sequentially sending a drainage
pipe and a flow injection
pipe in, and arranging sealing sections I and II; opening a valve I and a valve III, injecting 30-60 MPa of supercritical CO2 into the flow injection
pipe until pressure indicating number declines suddenly; opening a valve II to enable a ground drainage
station to drain the
coal bed gas, recording initial gas flow, repeating replacement of coal bed gas with CO2 when coal bed gas flow declines 30% of the initial gas flow again, and stopping coal bed gas drainage until the coal bed gas flow declines to 16% of the initial gas flow finally. By the
system and the method, concentration of drained coal bed gas is increased effectively, and cost for separation and purification is lowered; supercritical CO2
jet flow is adopted to break coal columns, so that threshold pressure is low, breaking speed is high, no
pollution is caused to a coal bed gas reservoir, and
rock breaking efficiency can be improved substantially.