华北中南部中高煤级构造煤瓦斯扩散规律及控制机理研究

发布时间：2018-05-18 23:14

  本文选题：构造煤 + 分形维数　； 参考：《河南理工大学》2016年博士论文

【摘要】：扩散在瓦斯运移产出过程中发挥着重要作用,针对以往构造煤瓦斯扩散特性研究多采用颗粒煤样和解吸扩散法进行,实验煤样和方法不能客观反映原始煤层物性特征和储层条件,控制机理缺乏结合煤的微观结构分析内外因素的耦合作用,现有扩散模型存在理想化程度高、准确性低、适用条件不明确等问题,从煤层在井下的实际赋存状态出发,采用气相色谱扩散法和解吸扩散法两种扩散系数测定方法,开展了模拟地层条件下构造煤瓦斯扩散规律实验,分析了两种方法反映构造煤瓦斯扩散规律的差异性和适用性,探讨了围压、气压、温度、煤质、煤体结构、微观结构等因素对瓦斯扩散规律影响及耦合控制机理,构建了反映不同地层条件下的构造煤瓦斯扩散模型,并对新模型进行了验证和应用,论文取得了以下主要研究成果:(1)探讨了四类煤体结构原煤柱状煤样制作方法,针对碎粒-糜棱煤柱状煤样制作困难这一难题,提出了构造煤等静压制作柱状煤样方法。(2)采用压汞、液氮吸附、小角X射线散射、扫描电镜等方法获取了构造煤微观孔裂隙的特性,提出了构造煤全孔径分形维数定量表征方法,为揭示构造煤瓦斯扩散控制机理奠定了基础。①无烟煤、贫煤孔容主要集中在微孔和过渡孔,肥煤孔容主要集中在过渡孔和中孔,而孔比表面积均集中在微孔;无烟煤、贫煤、肥煤的总孔容、总比表面积、退汞效率随破坏程度增大而增大,中值孔径、排驱压力随破坏程度的增大而减小,但在不同的破坏阶段,增加或减小的速率不同。②相同孔径段,小角X射线散射测定的孔比表面积明显大于液氮吸附所测结果,高出1.7~8.8倍左右,以无烟煤增幅最大,可能由封闭孔隙含量增多导致。③定义并提出了构造煤全孔径分形维数计算方法,实现了不同有效测试范围内压汞和液氮吸附分形维数的有效统一,便于对构造煤非均质性进行定量表征。④无烟煤、贫煤、肥煤显微裂隙发育总数随破坏程度的增大呈现先增大后减小的变化规律,以碎裂煤最为发育。(3)采用气相色谱法对柱状煤样和解吸法对颗粒煤样进行了扩散系数测定,研究了两种方法反映构造煤瓦斯扩散规律的差异性和适用性,探讨了围压、气压、温度、破坏程度等不同地层条件下构造煤瓦斯扩散规律。①搭建了气相色谱法模拟原始地层条件瓦斯扩散系数测定试验平台。②气相色谱法采用原煤柱状煤样进行测试,可同时施加有围压、气压、温度影响,解吸法采用颗粒煤样进行测试,仅施加有气压、温度,未考虑围压影响,两种扩散系数测定方法都反映了构造煤的瓦斯扩散规律,但属于不同的地层赋存状态,两者不能简单替代;前者主要应用于原始煤层扩散速率预测与评价,后者主要应用于瓦斯含量测定过程中损失量计算。③气相色谱法测定的无烟煤、贫煤、肥煤四类煤扩散系数随围压的增大呈现指数关系减小;随气压的增大呈现指数关系增大;随温度的升高呈现指数关系增大;在相同围压、气压、温度条件下,无烟煤、贫煤、肥煤四类煤扩散系数随着破坏程度的增加呈现先增大后减小的变化规律;相同破坏程度煤样随着变质程度增大呈现出先增大后减小的变化规律。④解吸法测定的无烟煤、贫煤、肥煤四类煤扩散系数随气压的增大呈现指数增大;随温度的升高呈线性关系增大;在相同的气压和温度条件下,无烟煤、贫煤、肥煤四类煤扩散系数随着破坏程度的增加而增大;相同破坏程度煤样随着变质程度增大而增大。这与气相色谱扩散法测定的构造煤扩散规律显著不同,反映了构造煤在不同地层条件下的瓦斯扩散规律。(4)分析了围压、温度、气压、煤质、煤体结构、微观孔裂隙结构等内外因素对瓦斯扩散规律的耦合影响及控制机理,构建了反映不同地层条件下的构造煤瓦斯扩散模型,并对新模型进行了验证和应用。①温度对不同地层状态下构造煤瓦斯扩散的影响基本一致,扩散系数均随着温度升高而增大,作用机理主要通过改变气体分子的均方根速度和平均自由程。②气压对构造煤扩散规律影响,宏观上均呈现扩散系数随气压升高而增大,但控制机理不同,分两种情况,一是当扩散煤样施加有围压影响时,受力学作用、吸附作用综合控制,其主控因素为有效应力作用;围压条件下构造煤扩散系数具有效应力负效应。二是当扩散煤样未施加围压影响,相当于卸压状态,气压主要改变吸附气体内外浓度差和气体分子均方根速度和平均自由程;卸压作用对煤样本身的微观孔隙结构也会产生重要影响,可能导致部分封闭、半封闭孔隙打开。③相同温压条件下,气相色谱法测定的扩散系数随着变质程度和破坏程度的增高呈现先增大后减小的变化规律,主要受微观孔隙结构和显微裂隙共同耦合控制。解吸法测定的构造煤扩散系数随着变质程度和破坏程度的增高而增大,主要受原始孔隙结构特征和原始微观结构受外界环境变化影响后再分布特征控制,其中微孔、细颈瓶孔、部分封闭孔起主导作用。由此可见,两种方法测定的扩散系数虽然都反映了构造煤的瓦斯扩散特性,但关键控制因素不同,各有特定的适用条件,两种方法测定的扩散系数不能简单替代使用。④依据影响构造煤瓦斯扩散规律的主控因素,选择不同的建模工具和原理,构建了反映不同地层条件下的构造煤瓦斯扩散模型:基于气相色谱法建立的构造煤瓦斯扩散耦合数学模型,可以实现对原始煤层条件下构造煤的瓦斯扩散系数预测与评价;基于解吸法的建立的构造煤分形-时效-Fick扩散模型,主要应用于瓦斯含量测定过程中损失量计算;新模型经理论和实践检验精度较高,满足生产要求。
[Abstract]:Diffusion is playing an important role in the process of gas migration and output. According to the previous research on the characteristics of coal gas diffusion, the particle coal sample and the desorption diffusion method are mostly used. The experimental coal samples and methods can not objectively reflect the physical characteristics and reservoir conditions of the original coal seam, and the control mechanism lacks the coupling of the microstructure analysis of the coalseam. The existing diffusion model has many problems, such as high degree of idealization, low accuracy and unclear application conditions. Starting from the actual condition of coal seam in the underground, two kinds of diffusion coefficient determination methods of gas chromatography diffusion method and desorption diffusion method are used to carry out the experiment of gas diffusion law under simulated formation conditions and analyze two kinds of methods. The method reflects the difference and applicability of the law of gas diffusion in structural coal, and discusses the influence of confining pressure, air pressure, temperature, coal quality, coal structure, microstructure and other factors on the law of gas diffusion and the mechanism of coupling control, and constructs a model of gas diffusion under different stratum conditions, which is verified and applied to the new model. The following main research results are obtained: (1) the method of producing column like coal samples for coal structure of four types of coal is discussed. In view of the difficult problem of making the clastic chype coal columnar coal, the method of making column like coal with isostatic pressure of tectonic coal is put forward. (2) using mercury pressure, liquid nitrogen adsorption, small angle X ray scattering and scanning electron microscopy to obtain the microstructure of coal. The characteristics of pore fissure, the quantitative characterization method of fractal dimension of total pore size of structural coal is put forward, which lays the foundation for revealing the mechanism of controlling the gas diffusion of structural coal. (1) anthracite coal, the pore volume of poor coal mainly concentrated in micropores and transition pores, and the pore volume of the fat coal mainly concentrated in the transition and middle holes, and the pore surface area is concentrated in the micropores; anthracite, lean coal and fertilizer The total pore volume of coal, the total specific surface area, the efficiency of mercury removal increases with the extent of damage, and the median pore size, displacement pressure decreases with the increase of damage degree, but the rate of increase or decrease is different at different stage of destruction. 2. The pore area of small angle X ray scattering measurement is obviously greater than that measured by liquid nitrogen adsorption, up to 1 About.7~8.8 times, the increase in the increase of anthracite coal is the biggest, which may be caused by the increase of closed pore content. (3) a method for calculating the fractal dimension of total pore size of structural coal is defined and proposed. The effective unification of the fractal dimension of pressure mercury and liquid nitrogen adsorption in different effective testing ranges is realized, and the quantitative characterization of the heterogeneity of structural coal is convenient. 4. Anthracite and lean coal, The total number of microfracture development of the fat coal increases first and then decreases with the increase of the damage degree. (3) the gas chromatography method is used to determine the diffusion coefficient of the cylindrical coal samples and desorption methods, and the differences and applicability of the two methods to reflect the law of gas diffusion in the tectonic coal are studied. A test platform for gas diffusion coefficient determination was built by gas chromatography to simulate the gas diffusion coefficient of original formation conditions. (2) gas chromatography was used to test the coal samples with coal column like coal, and the influence of confining pressure, air pressure, temperature, and desorption were applied at the same time. Coal samples are tested with only air pressure, temperature and no consideration of the influence of confining pressure. The two methods of determination of diffusion coefficient reflect the law of gas diffusion of the tectonic coal, but they belong to different strata, and the two can not be replaced simply. The former is mainly applied to the prediction and evaluation of the diffusion rate of the original coal seams, and the latter is mainly applied to the gas content measurement. The four types of coal diffusion coefficient of coal, poor coal and fat coal decreased exponentially with the increase of confining pressure, and increased exponentially with the increase of pressure; under the same confining pressure, pressure and temperature, the four types of coal, anthracite, lean coal and fat coal The diffusion coefficient increases first and then decreases with the increase of damage degree; the coal sample with the same damage degree increases first and then decreases with the increase of metamorphism. (4) the four types of coal diffusion coefficient of anthracite, lean coal and fat coal determined by the method of desorption increase exponentially with the increase of pressure; linear with the increase of temperature Under the same air pressure and temperature conditions, the four kinds of coal diffusion coefficient of anthracite, lean coal and fat coal increases with the increase of damage degree, and the same destruction degree increases with the degree of metamorphism. This is significantly different from the gas chromatography diffusion method for structural coal diffusion rules, which reflects the conditions of different formation coal in different formation conditions. The law of gas diffusion below. (4) the coupling influence and control mechanism of internal and external factors such as confining pressure, temperature, pressure, coal quality, coal structure, micro pore fracture structure and other internal and external factors on the law of gas diffusion are analyzed, and a model of gas diffusion in different formation conditions is constructed, and the new model is verified and applied. (1) temperature to different strata The influence of the diffusion coefficient of coal gas diffusion is basically the same, the diffusion coefficient increases with the increase of temperature. The mechanism of action is mainly by changing the root mean square velocity and the average free path of the gas molecules. 2. The influence of gas pressure on the diffusion law of the tectonic coal shows that the diffusion coefficient increases with the increase of air pressure on macro, but the control mechanism is different, two The first is that when the diffusion coal is affected by confining pressure, it is subjected to mechanical action and the adsorption is controlled synthetically. The main controlling factor is effective stress, and the structural coal diffusion coefficient has effect negative effect under confining pressure. Two is when the diffusion coal samples are not affected by confining pressure, and the pressure mainly changes the internal and external concentration of the adsorbed gas. Degree difference and the mean square root velocity and average free range of the gas molecules; the pressure relief effect also has an important effect on the micro pore structure of the coal sample itself, which may lead to partially closed and semi closed pores open. 3. The diffusion coefficient of gas chromatography is first increased and then decreased with the increase of quality and the degree of destruction under the same temperature and pressure conditions. The small change law is mainly controlled by micropore structure and microscopic fissure. The diffusion coefficient of structural coal measured by desorption increases with the increase of metamorphism degree and degree of destruction, and is mainly controlled by the redistribution characteristics of the original pore structure and the original microstructure after the changes of the external environment. It can be seen that the diffusion coefficients measured by the two methods reflect the gas diffusion characteristics of the tectonic coal, but the key control factors are different, each has the specific applicable conditions. The diffusion coefficient measured by the two methods can not be replaced simply. By choosing different modeling tools and principles, the gas diffusion model of structural coal is constructed under different stratum conditions: a mathematical model of gas diffusion coupling based on gas chromatography is established, which can be used to pre test and evaluate the gas diffusion coefficient of structural coal under the condition of original coal seam. The shape time -Fick diffusion model is mainly applied to the calculation of the loss of gas in the process of gas content determination. The new model has high accuracy in theory and practice to meet the production requirements.
【学位授予单位】：河南理工大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：TD712
，

本文编号：1907632