The influence of gas injection pressure and osmotic pressure on the permeability of loose coal body at different temperature conditions
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摘要:
为了探究采空区遗煤自燃过程中温度对松散煤体渗透率的影响机理，综合考虑温度引起的煤体吸附变形、热膨胀变形、热裂变形以及滑脱效应等因素对煤体渗透率的影响，建立了不同温度下煤体渗透率数学模型,通过控制变量法控制渗透率数学模型单一影响因素参数来研究温度变化对松散煤体渗透率的影响机理。基于物理相似原理，设计搭建了松散煤体渗流实验平台，选取山西成庄矿无烟煤为实验对象，以空气为渗流气体模拟井下环境，开展了不同温度（40～100 ℃）、不同注气压力（0.3～0.5 MPa）、不同渗透压力（0.04～0.08 kPa）条件下松散煤体中气体运移实验，通过实验与模型结果相互验证来探究温度变化对松散煤体渗透率的影响机理。结果表明：松散煤体渗透率随气体压力梯度增加呈指数型递增；同一压力梯度条件下，渗透率随温度升高逐渐减小，40～60 ℃时温度对渗透率影响较小，渗透率变化不明显，60 ℃之后渗透率开始明显降低，90、100 ℃时渗透率降低更为显著；受滑脱效应影响，注气压力的升高抑制煤体渗透率；不同渗透压下（0.04～0.08 kPa），松散煤体渗透率模型值与渗流实验值吻合度高，随着温度的升高吸附形变对松散煤体渗透率有抑制作用，热裂形变和滑脱效应对松散煤体渗透率有促进作用，热膨胀变形对松散煤体渗透率影响微弱，温度通过吸附形变、热裂形变及滑脱效应综合作用影响松散煤体渗透率。
Abstract:In order to investigate the influence mechanism of temperature on the permeability of loose coal body in the process of spontaneous combustion of residual coal in the gob, the mathematical model of the permeability of coal body under different temperature conditions was established by considering the effects of temperature-induced adsorption deformation, thermal expansion deformation, thermal fission deformation and sliding effect, etc., and the parameters of the single influencing factors of the mathematical model of the permeability were controlled by the method of controlling variables to investigate the influence mechanism of the temperature change on the permeability of the loose coal body. Based on the principle of physical similarity, an experimental platform for loose coal seepage was designed and constructed, and anthracite coal from Chengzhuang Mine in Shanxi Province was selected as the experimental object, and air was used as the seepage gas to simulate the underground environment, so that gas transport experiments were carried out in the loose coal body under different temperature conditions (40-100 ℃), different injection pressures (0.3-0.5 MPa), and different permeability pressures (0.04-0.08 kPa). The mechanism of the influence of temperature change on the permeability of the loose coal body was investigated by mutual verification of the experimental and modeling results. The results show that: the permeability of loose coal body increases exponentially with the increase of gas pressure gradient; under the condition of the same pressure gradient, the permeability decreases gradually with the increase of temperature; the influence of the temperature on the permeability is small when it is from 40 ℃ to 60 ℃, and the change of the permeability is not obvious, and the permeability starts to decrease after 60 ℃, and the decrease of the permeability is more significant when it is from 90 ℃ to 100 ℃; under the influence of the slippage effect, the increase of the injection pressure inhibits the permeability of the coal body. Under different osmotic pressure conditions (0.04-0.08 kPa), the model values of the permeability of the loose coal body and the experimental values of the seepage flow are in high agreement. With the increase of temperature, adsorption deformation has an inhibitory effect on the permeability of the loose coal body, thermal cracking deformation and the slipping effect have a promotional effect on the permeability of the loose coal body, and the effect of the deformation of the thermal expansion on the permeability of the loose coal body is weak. Temperature affects the permeability of loose coal body through the combined effect of adsorption deformation, thermal cracking deformation and sliding effect.
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图 1 松散煤体渗流特性参数实验装置
Figure 1. Experimental device for seepage characteristic parameters of loose coal body
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图 2 不同温度下煤样渗透率变化规律
Figure 2. Changes in coal sample permeability at different temperature conditions
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图 3 煤样压力梯度渗透率变化规律
Figure 3. Changes of coal sample permeability with different pressure gradients
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图 4 不同注气压力下温度/压力梯度渗透率曲线
Figure 4. Temperature/pressure gradient permeability curves at different gas injection pressures
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图 5 渗透压力为0.04~0.08 kPa不同温度下渗透率实验值与模型值对比图
Figure 5. Comparison between experimental and model permeability values at different temperatures when osmotic pressure is 0.04-0.08 kPa
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图 6 有无考虑滑脱效应、热膨胀变形、吸附变形和热裂因素下煤体渗透率对比图
Figure 6. Comparison of coal permeability with or without consideration of slippage effect, thermal expansion deformation, adsorption deformation and thermal cracking factors
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图 7 升温前后渗流通道变化示意图
Figure 7. Schematic diagrams of seepage channel change before and after heating
表 1 不同压力梯度渗透率最终损失率
Table 1 Final permeability loss rates of different pressure gradients
压力梯度/（Pa·m−1） 渗透率损失率/% 60 17.96 80 16.28 100 18.06 120 20.00 140 20.72 160 23.92 180 26.76 
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表 2 渗透模型引用参数
Table 2 Reference parameters of permeability model
参数 参数值 参数来源 EA/MPa 1 900 文献[19] ρc/（g·cm−3） 1.483 9 自测 ϕ0 0.504 8 自测 $ \vartheta $ 23.7 自测
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表 3 无烟煤等温吸附常数
Table 3 Anthracite isotherm adsorption constants
温度/℃ a b 40 6.520 12.0 50 6.127 10.0 60 5.802 12.0 70 5.460 9.8 80 5.326 12.0 90 5.220 11.0 100 5.100 12.0
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1. 柳昭星. 奥陶系灰岩顶部劈裂注浆裂隙起裂机制试验研究. 采矿与安全工程学报. 2023(01): 204-214 . 
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