【作者】 周俊；

【导师】 李增华；

【作者基本信息】 中国矿业大学 ， 安全科学与工程， 2018， 硕士

【摘要】 针对无保护层开采条件的近距离突出煤层群区域防突问题,通常采用底板岩巷上向穿层钻孔预抽最底层煤层瓦斯,并以该煤层作为下保护层,开采上部煤层。但是,突出煤层群的下部煤层瓦斯压力更高,其突出危险性往往高于上部煤层,钻孔施工困难,成孔率较低,因此也可采用顶板岩巷下向穿层钻孔预抽最上层煤层瓦斯,并将其作为上保护层,保护下部煤层开采。然而,由于我国矿井水文地质条件复杂,多数煤层顶板存在含水层,下向穿层钻孔抽采煤层瓦斯过程中,顶板水通过钻孔侵入煤层孔隙,并在钻孔周围形成局部水饱和区域。与正常煤层中的渗流不同,在水侵煤层中,由于水饱和煤体区域及钻孔积水的封堵作用,煤层中的瓦斯将在孔隙压力的作用下会溶解到孔隙水中,进而在浓度梯度影响下以扩散方式在饱和水煤体区域及钻孔水中运移,最终,在抽采负压下从钻孔水中解析后进入抽采系统。瓦斯在水饱和煤层区域中的运移过程与一般的煤层瓦斯运移存在明显差异,研究该运移过程及其影响因素对认识水侵煤层瓦斯运移特性、指导水侵煤层瓦斯抽采等具有重要意义。本文通过理论分析,实验研究及数值模拟的方法深入探讨了瓦斯在水及饱和水煤体中的扩散运移特性,建立了水侵煤体瓦斯运移数学模型。最终,以青东煤矿726工作面为现场工程试验对象,验证了该模型的准确性,研究成果可对水侵煤体瓦斯抽采提供一定的理论指导。具体内容如下:首先,实验研究了瓦斯在水溶液中的溶解规律,分析了平衡压力、温度、盐离子(Ca²⁺,Na⁺)对瓦斯溶解度的影响。研究表明,在低温条件下,温度对瓦斯的溶解度影响效果较弱,实验温度区间内（25⁴0℃）,瓦斯溶解度随温度的升高而小幅度降低。瓦斯在水中的溶解度受实验平衡压力的影响较为显著,随着平衡压力的升高而增大,在实验压力范围内成线性关系,此规律在温度较低时更加明显。基于压力衰减法开展了不同实验条件下瓦斯在水中的扩散规律研究,分析了初始压力、实验温度对瓦斯扩散系数的影响。实验结果表明,瓦斯在水中的扩散系数受初始压力的影响较大,随初始压力的升高而逐渐增加,但增加的幅度逐渐变小,符合指数衰减关系。瓦斯在水中的扩散系数与温度有关,随着实验温度的升高而逐渐增加,成线性关系。进一步研究了瓦斯在水饱和煤样中的扩散规律,主要分析了煤样迂曲度、实验温度、压力的影响。结果表明,相同实验条件下瓦斯在水饱和煤样中的有效扩散系数比其在水中扩散系数要小许多。同时,随着水饱和煤样的迂曲度的增大,瓦斯在孔隙水中的扩散通道更曲折,其有效扩散系数也逐渐减小。实验温度及压力对瓦斯在水饱和煤样中的有效扩散系数影响效果与前文基本一致。此外,通过拟合数据分析了实验温度、初始压力对瓦斯有效扩散系数的影响权重,符合关系式:ln?=-109.490+15.547ln?+0.045ln?,说明两者的影响权重存在差异明显,温度对瓦斯在水中的扩散系数的影响力明显大于压力的影响力。构建了瓦斯在水侵煤层中运移模型,运用COMSOL数值模拟软件预测了瓦斯抽采量及瓦斯卸压效果。通过对比青东矿瓦斯抽采数据,验证了数值结果的合理性。研究了瓦斯扩散系数、煤层渗透率和水饱和半径对瓦斯抽采量及卸压效果的影响,结果表明,残余瓦斯压力随扩散系数的增大而减小,随水饱和区域半径的增大而增大。煤层渗透率对瓦斯抽采效果的影响较为为复杂:高渗透率煤层整体抽采效果较好,而在低渗透率煤层中,仅钻孔周围煤体的抽采效果较好。更多还原

【Abstract】 For controlling the coal and gas outburst of coal seam group,the bottom seam gas is usually pre pumped to the bottom layer by the floor rock roadway,and the coal seam is exploited as the lower protective layer.However,the gas pressure in the lower coal seam of the outburst coal seam group is higher,its outburst risk is often higher than the upper coal seam,and the drilling construction is difficult and the pore forming rate is low.Therefore,the top layer of the top layer rock roadway can be used to pre draw the top coal seam gas under the roof rock roadway,and it is used as the upper protective layer to protect the lower coal mining.However,because of the complex hydrogeological conditions in the mine,most of the coal seam roof has aquifers.In the process of coal seam gas extraction,the roof water invades the pores of the coal seam through drilling and forms the local water saturation area around the borehole.In the water invasion coal seam,the gas in the coal seam will dissolve into the pore water under the effect of pore pressure,and then,under the influence of the concentration gradient,in the saturated water coal body region and the borehole water.There are obvious differences between the migration process of gas in the water saturated coal seam area and the general coal seam gas migration.It is of great significance to study the migration process and its influencing factors to understand the gas migration characteristics of the water invasion coal seam and to guide the gas extraction of the water invasion coal seam.Through theoretical analysis,experimental research and numerical simulation,the diffusion and migration characteristics of gas in water and saturated water coal body are discussed,and a mathematical model of gas migration is established.Finally,the accuracy of the model is verified by the 726 working face of the Qing Dong coal mine.The results can provide some theoretical guidance for the gas extraction of the coal body.The specific contents are as follows:Experiments were conducted to determine the solubility of gas under different conditions of temperature,pressure,and salt solution.The study shows that under low temperature conditions,the effect of temperature on the solubility of gas is weak.In the experimental temperature range,the gas solubility decreases slightly with the increase of temperature.Different from the influence of temperature,the solubility of gas in water is significantly affected by the experimental equilibrium pressure,and increases with the increase of equilibrium pressure.The diffusion coefficient of gas in pure water under different temperature and pressure was measured by pressure decay method.The experimental results show that the diffusion coefficient of gas in water is greatly affected by the initial pressure,which is in line with the exponential decay relationship,that is,it gradually increases with the increase of the initial pressure,but the increase range decreases.In addition,the equilibrium pressure of the gas is linearly related to the initial pressure,that is,the higher the pressure of the gas charged into the diffusion chamber,the higher the pressure during the diffusion equilibrium.The diffusion coefficient of gas in water is related to temperature,and it gradually increases with the increase of experimental temperature,which is a linear relationship.Experiments were carried out to determine the diffusion coefficient of gas in coal saturated with water under different temperature and pressure and its influencing factors.The results show that the porosity and curl of the water-saturated coal sample have a certain influence on the effective diffusion coefficient of gas.With the increase of the degree of curl of the water-saturated coal sample,the diffusion path of gas in pore water is more tortuous and its effective diffusion.The effect of experimental temperature and pressure on the effective diffusion coefficient of gas in water saturated coal samples is basically the same as before.In addition,through the fitting data,the influence weight of the experimental temperature and initial pressure on the effective diffusion coefficient of gas is analyzed,which conforms to the formula: ln? =-109.490 + 15.547ln? + 0.045ln?,which shows that the influence weight of the two is obviously different,and the influence of temperature on the diffusion coefficient of gas in water is obviously greater than that of the pressure.A model for gas migration in water-intrusion coal seams was constructed.The COMSOL numerical simulation software was used to predict the gas drainage volume and the gas pressure relief effect.By comparing the actual gas drainage results of Qingdong Mine,the rationality of the numerical model was verified.The results show that the gas pressure decreases with the increase of the diffusion coefficient and increases with the radius of the water saturation region.The influence of coal seam permeability on gas pressure is more complicated: the high permeability coal seam has better overall drainage effect,but in the low permeability coal seam,the drainage effect of the surrounding coal body is only good.更多还原