Simulation on water jet slotting-nitrogen injection displacement combined with gas drainage
Aiming at the difficulty of gas extraction in low permeability coal seams,a combined gas ex-traction process of water jet slotting-nitrogen injection displacement is proposed,and the process flow and principle were analyzed.Through numerical simulation,control models and slotted coal seam mod-els were established,and the effects of hole spacing and gas injection pressure on nitrogen injection dis-placement effect in different coal seams were investigated,respectively.The influence range of nitrogen injection in different coal seams under the same conditions is compared,and the influence of coal seam slotting on nitrogen injection displacement effect is studied.The results show that:When the hole spac-ing is increased from 3 m to 7 m for 20 days,the influence range of gas injection in control coal seam is reduced from 6.5 m to 2.2 m,while that in slotted coal seam is reduced from 7.9 m to 3.6 m.When the gas injection pressure is increased from 1.0 MPa to 3.0 MPa for 20 days,the influence range of gas injection in control coal seam is increased from 1.0 m to 5.3 m,and the influence range of gas injec-tion in slotted coal seam is larger than that in control coal seam under the same gas injection pressure.The main influence of coal seam slotting on nitrogen injection displacement is in the horizontal direc-tion.The slotting area is adjacent to the slot and communicates with each other to form an elliptical composite area.Under the condition of 10 d,20 d and 30 d extraction,the influence range of gas injec-tion in control coal seam is 1.56 m,2.65 m and 6.51 m,respectively,while that in slotted coal seam is 2.16 m,5.75 m and 11.55 m,respectively.Coal seam slotting can effectively improve the decreasing rate of gas pressure,and the simulation results are basically consistent with the field industrial test re-sults.Nitrogen injection in slotted coal seam can effectively improve the influence range of gas injection and enhance the effect of gas extraction,which provides reference for further research on combined gas extraction technology.
combined processgas extractionslotting gas injectioninfluence range of gas injectioncoal seam gas pressure
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