Study On Nitrogen Injection And Production Increasing Technology In Coalbed Methane Wells

The coal reservoirs in the south of the Shizhuang area of the Qinshui Basin are characterized by“three lows and one high”.The reason for the low productivity of the CBM wells is due to geological factors,and may also be caused by engineering factors.In this paper,nitrogen injection is used to improve the recovery of coalbed methane,and nitrogen injection experiments and numerical simulations are carried out for coal seam gas of 3~#coal in Shizhuang South.In terms of engineering factors,the decrease in permeability caused by reservoir damage and clogging of coal powder is the main reason for the low productivity.Through indoor experiments,the effects of nitrogen injection time,pressure,temperature,and well-removal time on coal rock permeability were studied.The results show that the nitrogen stress induces the change of coal rock stress;the permeability of coal rock first decreases with a certain extent after nitrogen injection,and finally reaches a stable value after a sudden increase;the greater the nitrogen injection pressure of coal rock,the higher the permeability improvement effect.obvious.In addition,in the experiment,it was found that the effect of low-temperature nitrogen gas on the coal rock permeability improvement is more significant,the lower the nitrogen injection temperature,the higher the permeability of the coal rock after nitrogen injection,and the penetration time of the rock pressure on the coal rock after the nitrogen injection.There is also a certain influence:the permeability of coal rock first increases with the increase of rolling time,and then the growth rate gradually decreases with time.The Langmuir adsorption curve and Fick’s law are used to describe the desorption and diffusion processes in coalbed gas,and a two-pore medium model is established.It is preferable that the construction parameters such as nitrogen injection throughput,nitrogen injection rate,total nitrogen injection,and well-removal time be used for production simulation of gas wells in the Shizhuang South coal seam.The simulations show that nitrogen injection in coalbed methane wells has a significant effect of increasing production and is an effective measure to increase production.Nitrogen injection is one of the measures for increasing production of coalbed methane,and the factors affecting the effect of nitrogen injection are not only the factors involved in this paper.However,in this paper,through indoor experiments and numerical simulations,we have initially formed a construction plan for nitrogen injection and production increase of coalbed methane vertical wells in the south of the Shizhuang area,and it is a good attempt to improve the nitrogen injection and production of high-rank coal.