Gas composition (%)
100 80 60 CO2 content, simulation N2 content, simulation
40
N2 content, experiment
CO2 content, experiment
20 0
0
5000
10000
15000
20000
25000
30000
Time (minute) Figure 4 Comparison of Gas compositions between experiment and simulation: 0.06mD permeability conditions Figure 6 N2 flushing field test in Metro coal mine
15
10
5
0
0
5000
10000
15000
20000
25000
30000
Time (minute) Figure 5 CO2 residual content comparisons between experiment and simulation: 0.06mD permeability conditions
FIELD TRIALS Four stages of N2 injection were carried out from 27 Oct to 21 Nov, 2016 in Metropolitan Colliery. Two boreholes with spacing of 10m were drilled on the rib in the gateroad. The length of the boreholes was 36m. One borehole was used for the injection of N2 and the other was used as the production borehole. Gas flow rate and gas composition were monitored and recorded.
SUMMARY Two N2 flushing tests were conducted and the flushing effect and efficiency was evaluated from different aspects. The tests demonstrated that N2 injection can significantly improve CO2 drainage efficiency. This technology can be considered for use in underground coal mines especially in the low permeability coal seams to improve gas drainage efficiency. The binary gas migration model can be used to illustrate the gas migration during the N2 enhanced gas drainage process. Compared the gas composition and the CO2 residual content with the laboratory tests, it can be observed that the simulation results match the laboratory results well. From field trials, we found that Nitrogen flushing can accelerate the gas flow between the injection and production boreholes.
REFERENCE Black, D., Aziz, N., Jurak, M., & Florentin, R. (2009). Outburst threshold limits-are they appropriate? Busch, A., & Gensterblum, Y. (2011). CBM and CO2-ECBM related sorption processes in coal: A review. International Journal of Coal Geology, 87(2), 49-71.
a) 27 Oct: stage one, 2 packs (around 300m3) of nitrogen were injected, gas samples from production borehole were collected during and after injection; b) 07 Nov: stage two, one and half packs (around 225m3) of nitrogen were injected, gas samples from production borehole were collected during and after injection; c) 15 Nov: stage three, water inflation packer was used to seal the borehole, five and half packs (around 825m3) of nitrogen were injected, gas flow from production borehole was measured and gas samples were collected during and after injection; d) 21 Nov: stage four, water inflation packer was used to seal the borehole, 1 pack (around 150m3) of nitrogen was injected, gas flow from production borehole was measured and gas samples were collected during and after injection.
Civil, Mining and Environmental Engineering 2015-2017 School Report
87
RESEARCH
Experimental Simulation
20
REPORTS: MINING
CO2 residual content (m3/t)
25