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Evaluation of underground coal gas drainage performance: mine site measurements and parametric sensitivity analysis
Process Safety and Environmental Protection ( IF 7.8 ) Pub Date : 2021-02-04 , DOI: 10.1016/j.psep.2021.01.054
Peng Liu , Jinyang Fan , Deyi Jiang , Jiajun Li

Underground gas extraction from coal formations has triple-effects involving mining safety, low-carbon gas capture and greenhouse gas control. Air leakage around the drainage borehole is a serious problem that continuously affects gas drainage performance. In this study, mine site measurement of gas drainage data is firstly performed in coal mine, and then a mechanism-based model is proposed to theoretically describe gas desorption and diffusion and flow through coal around the drainage borehole. Further, the propose model is numerically solved and verified with borehole drainage data measured in mine site. Followed this, the validated mechanism-based model is implemented to conduct parametric studies. The results showed that: (a) as the fracture permeability increases from 3 × 10-22 m2 to 3 × 10-14 m2, the air leakage flux increases from 7355 m3/d to 18303 m3/d, and the gas concentration decreases from 46.9% to 12.7%, it indicates that changing the permeability around the borehole may be a wise strategy to control air leakage; (b) the coal matrix parameters (including permeability, sorption constant and radius of matrix) have a dynamic impact on gas drainage performance at the different stage of gas drainage. For example, the increment of methane production induced by increasing the sorption constants does not exceed 3.3% at the drainage time ∼0.34 day; while the growth increases to more than 19.5% at the drainage time ∼ 9.75 days; (c) at the initial stage of extraction gas production is mainly determined by the fracture flow. A higher permeability of coal fracture will incur more air leakage flux, reducing gas concentration in drainage borehole; (d) whereas, the matrix parameters dominate gas flow at a later stage. Increasing matrix permeability, sorption property or decreasing the matrix radius will enhance the gas exchange flux from the pore system of coal matrix to the fracture system, subsequently incurring a higher concentration/production of drainage gas. The simulated result and field tests demonstrates that sealing on the coal wall around the borehole can block a portion of air leakage paths and reduce air leakage linearly, which illuminates a more efficient strategy to minimize air leakage for underground gas extraction.



中文翻译:

地下瓦斯抽采性能评估:矿山现场测量和参数敏感性分析

从煤层中开采地下气体具有三方面的影响,涉及采矿安全,低碳气体捕获和温室气体控制。排水孔周围的漏气是一个严重的问题,不断影响着瓦斯的排水性能。本文首先对煤矿瓦斯抽采数据进行了实地测量,然后提出了一种基于机理的模型,从理论上描述了瓦斯抽放井眼周围瓦斯的解吸扩散和流向。此外,用矿场中测得的井眼排水数据对提出的模型进行了数值求解和验证。随后,实施经过验证的基于机制的模型来进行参数研究。结果表明:(a)随着裂缝渗透率从3×10 -22增加 m 2到3×10 -14  m 2,漏风量从7355 m 3 / d增加到18303 m 3 / d,瓦斯浓度从46.9%下降到12.7%,表明井眼周围的渗透率发生了变化。控制空气泄漏可能是一个明智的策略;(b)煤层气参数(包括渗透率,吸附常数和基体半径)对瓦斯抽放不同阶段的瓦斯抽采性能有动态影响。例如,在约0.34天的排水时间,通过增加吸附常数引起的甲烷产量增加不超过3.3%;在排水时间〜9.75天时,生长速度增加到19.5%以上;(c)采出气的初始阶段主要由裂缝流量决定。较高的煤层破裂渗透率将导致更多的漏气通量,从而降低排水井眼中的瓦斯浓度。(d),而矩阵参数在以后阶段支配着气流。增加基体渗透率,吸附性能或减小基体半径将增强从煤基体孔隙系统到裂缝系统的气体交换通量,从而导致较高的排泄气体浓度/产量。模拟结果和现场测试表明,在井眼周围的煤壁上进行密封可以阻塞一部分漏气路径并线性地减少漏气,这为减少地下气体抽取的漏气提供了一种更为有效的策略。

更新日期:2021-02-04
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