Research On Effects Of Methane Displacement By Nitrogen-injection Along With Drilling Length

“The rule of preventing coal and gas outburst” was published in August2009,which is based on the document of “The detailed regulations of preventing coal and gasoutburst”, as well as the measure of prophylaxis and cure in advance and force onregional outburst prevention, thus transport the focus and gateway of outburstprevention from portion to key areas. In this thesis, research on the regulation of holeslength variation when injecting nitrogen into coal seams was applied in test minesuccessful because of the inspiration from experimental study on “underground gasinjection for the methane mechanism and the law of coal seam” by Yang Hongming.This paper caught on numerical simulation and field experimental study around theproblems of gas injection along with holes length variation as well as the effect ofreplacing methane in coal-bed. Based on Darcy percolation theory, Fick diffusion theory,Langmuir adsorption theory and gas state equation, established the model of gas flowand displacement desorption under the multi-physics coupling condition, then usingComsol Metaphysics’ finite element simulation software to conduct numericalsimulation of coal seam gas injection. On this basis, the research on the regular of holeslength variation when injecting methane into coal seams was conducted in the StoneHarbor coal mine. We got the law of holes length variation when it comes to injectinggas to replace methane in coal-bed under different conditions of gas injectionpressure after research on Lane No.8Drill Field in Return Airway15109and Lane No.6Drill Field in Return Airway15203.By the research on the effect of gas injection in Stone Harbor coal seam, andthrough the experiment of field seam gas injection, we got that not only does the seamoccurrence conditions, but also the basic parameters of gas injection and mine sealedinfect the effect of replacing methane in coal seam.Gas injection is a motive process under coupling conditions with seepage flow,diffusion, replacement adsorption-desorption. Based on Darcy percolation theory, Fickdiffusion theory, Langmuir adsorption theory, multi-physics coupling mathematicalmodels was established and numerical simulation of coal seam gas injection wasconducted. The result showed that the smaller gas injection pressure, the greater attenuation gradient of pressure in the hole, and then the more pressure reduce in thedeeper hole. Similarly, vice versa. Regardless of the measure of “injection along withdischarge” or “injection along with pumping”, the efficiency of along holes lengthchelating gas content is several times than pumping or discharging separately and themore time for the measures, the greater chelating efficiency.Experiments of injecting other gas to discharge methane were conducted on LaneNo.8Drill Field in Return Airway15109and Lane No.6Drill Field in Return Airway15203in the coal mine. The results showed that when injecting0.65MPa into coal mine,the pressure attenuation gradient along with the hole deep would be0.23MPa/100m.This means holes length variation associates with pressure as well as the time of gasinjection. Specifically, the greater pressure of injection gas, the smaller attenuationgradient of gas along with the hole deep; and the longer gas injection, the greaterattenuation gradient.