Zuo Weiqin, Li Liwen, Liu Yanwei, Han Hongkai, Cui Peiwen
School of Safety Science and Engineering, Henan Polytechnic University, Jiaozuo 454000, China.
State Key Laboratory of Coal Mine Disaster Dynamics and Control, Chongqing University, Chongqing 400044, China.
ACS Omega. 2024 Aug 30;9(37):39051-39064. doi: 10.1021/acsomega.4c05820. eCollection 2024 Sep 17.
N injection into coal seams can effectively enhance the gas flow capacity in the late stage of pumping, thereby improving the recovery rate and recovery efficiency of low coalbed methane (CBM). To reveal the thermodynamic flow coupling relationship between the reservoir and the gas phase and its transportation mechanism in the process of thermal N injection, a mathematical coupling model of N injection that considers the deformation of the coal seam, fluid transportation, and temperature change was established. The influence of the seepage heat transfer effect of the coal seam under the effect of N injection on the CH extraction rate was investigated using this model. Results indicate that the action mechanism of N injection in coal seams includes increasing seepage, promoting flow, and displacing gases. A higher initial coal seam temperature results in a smaller thermal expansion and deformation of the coal skeleton during thermal N injection and less pronounced coal permeability increase. A larger initial coal seam permeability results in more favorable N diffusion, which strengthens the flow-promoting effect on CH. The effect of gas injection pressure on CH recovery is greater than that of the gas injection temperature: High pressure promotes N seepage, carries CH flow, and increases the CH diffusion effect, whereas higher temperature promotes the desorption of adsorbed gas in the coal seam and improves the recovery rate.
向煤层注入氮气可有效提高抽采后期的瓦斯流通能力，从而提高低煤层气（CBM）的采收率和开采效率。为揭示热注氮过程中储层与气相之间的热力流耦合关系及其运移机制，建立了考虑煤层变形、流体运移和温度变化的注氮数学耦合模型。利用该模型研究了注氮作用下煤层渗流传热效应对煤层气抽采率的影响。结果表明，注氮在煤层中的作用机制包括增加渗流、促进流动和驱替气体。煤层初始温度越高，热注氮过程中煤骨架的热膨胀和变形越小，煤层渗透率增加越不明显。煤层初始渗透率越大，越有利于氮气扩散，从而增强对煤层气的促流作用。注气压力对煤层气采收的影响大于注气温度：高压促进氮气渗流，携带煤层气流动，增加煤层气扩散效应，而较高温度促进煤层中吸附气的解吸，提高采收率。
