【作者】 张时音；

【导师】 桑树勋；

【作者基本信息】 中国矿业大学 ， 地球化学， 2009， 博士

【摘要】 基于地层条件下煤储层固-液-气三相耦合体系的地质事实,以IS-100等温吸附解吸仪和MTS815型电液伺服岩石实验系统为主要实验平台,对采自新疆、肥城、鄂尔多斯和沁水盆地的煤样进行高压注水实验和等温吸附实验。发现储层条件下煤层中的液态水对煤基质吸附气体存在显著影响;从表面物理和界面化学层面,通过对范德华力、气相分子间作用力和煤基质表面作用势能定量分析,建立了煤储层固-液-气相间作用物理化学模型,揭示了不同实验条件煤吸附甲烷特征的物理化学机理。通过吸附扩散动力学分析和吸附扩散系数计算,揭示了不同压力和水分条件下的煤吸附甲烷的吸附扩散动力学特征。通过实验数据拟合和理论分析,区分出了Langmuir模型和Dubinin-Radushkevich模型的适应性条件。实验方法的改进和有关煤储层相间作用机理的揭示,将影响对煤层储气、产气的相关认识,对煤层气勘探开发生产有现实意义。煤储层固-液-气三相耦合体系煤吸附甲烷气体本质是以范德华力作用为主的物理吸附,吸附能力的大小取决于不同相态水分子影响下的煤分子与气体分子间作用力的大小。由于强氢键作用,平衡水煤样中气态水分子优先吸附于煤基质表面,使煤基质表面吸附势能较干燥煤样低。注水煤样中的液态水在高压下进入煤体孔裂隙内并润湿煤基质表面形成单分子层水膜,甲烷气体受到润湿煤基质和水膜的共同作用吸附在煤基质表面,此时煤分子与甲烷分子间范德华作用力相对于干燥煤样要小,而相对于平衡水煤样要大,煤基质表面吸附势能低于干燥煤样而高于平衡水煤样。对于不同煤级煤样,与孔隙结构相关的煤体润湿性决定了煤基质吸附甲烷气体能力大小。煤吸附甲烷实验过程中,煤的气体扩散速率决定了整个吸附实验过程的快慢。由于实验粒级小的煤样其总表面积大且扩散路径复杂,因而吸附扩散系数较粒级大的煤样小。对于不同煤级煤样,孔隙度大的煤样吸附扩散系数大,所以孔隙结构的变化是吸附扩散系数变化的主要原因。平衡水煤样中气态水的存在,增加了气体流动的介质粘度,降低了煤基质吸附甲烷的能力,扩散系数较干燥煤样低。注水煤样中的液态水润湿煤基质表面形成水膜,介质粘度较平衡水煤样偏差不大,但润湿煤基质和水膜的作用力较平衡水煤样高,吸附甲烷能力强,所以注水煤样的扩散系数较平衡水煤样高,但低于干燥煤样。所有的理论模型都有假设条件,所以Langmuir模型和Dubinin-Radushkevich模型适用的储层压力的范围和煤样的类型都不同。对于低煤级的含水煤样,Dubinin-Radushkevich模型适应的储层压力的范围大于Langmuir模型,所以Dubinin-Radushkevich模型适应性较好;而中高煤级的含水煤样Langmuir模型的拟合度较Dubinin-Radushkevich模型高,所以Langmuir模型适应性较好。更多还原

【Abstract】 Based on the geology situation of solid-liquid-gas coupling system in coal reservoir under stratigraphic condition, the isothermal adsorption/desorption water system model (IS-100) and electrohydraulic servo rock system (MTS815) were used to carry out the injection experiments under high pressure and isothermal adsorption experiments using coal samples which are from Sinkiang, Feicheng, Ordos and Qinshui basin. The results suggested that the methane adsorbability of coal matrix is remarkably influenced by liquid water exist in coals. According to the quantitative analyses of Van der waals force, gas interaction force and superficial potential force of coal matrix, the physical chemistry model of solid-liquid-gas interaction in coal reservoir which revealed the physical chemistry mechanisms of coal adsorption under different experimental conditions, was established from the physic and chemistry point of view. Adsorption diffusion dynamic characteristics of methane adsorption were indicated under different pressure and water content by calculating the adsorption diffusion coefficient and analyzing the adsorption diffusion dynamic. Adaptability conditions of Langmuir and Dubinin-Radushkevich model were distinguished based on experimental fitting data and theory analyzing. Therefore, the improvement of experiment method and investigation of solid-liquid-gas interaction mechanism of coal reservoir will influence the understandings of gas storage and production, and these are significant to coalbed methane exploration and development.The essence of methane adsorption by coal is physical adsorption (mainly the Van der waals force) in the solid-liquid-gas coupling system, coal adsorption capacity is decided by the intermolecular force between coal and methane molecule which is influenced by different phase water. Gaseous water in moisture-equilibrated coal sample is easier to be adsorbed on the coal surface than that of methane because of the hydrogen bond, which makes adsorption potential of coal surface lower than that of dry coal sample. As for water injection sample, liquid water enters fissures and pores, making the coal surface wet and forming monomolecular water layer under high pressure. Then methane is absorbed on the coal surface because of the Van der waals force from wet coal matrix and water film. This Van der waals force between wet coal matrix and methane of water injection sample is lower than that between dried coal matrix and methane of dried sample but it is higher than the force of moisture-equilibrated sample, and so does superficial potential of water injection sample. Coal wettability, which is related with pore structure, determines the adsorption capacity of samples with regard to different coal rank. In adsorption experiment, adsorption diffusion rate of coal dominates the speed of methane adsorption process. Adsorption diffusion rate of big grain size sample is higher than small one which has bigger total surface area and the more complicated diffusion path. The diffusion rate of high porosity sample is higher than that of low porosity sample in different coal rank. Consequently, pore structure is the reason that mainly influences the adsorption diffusion coefficient of coal. Gaseous water in moisture-equilibrated sample increases the medium viscosity of gas moving and decreases coal adsorption capacity; therefore adsorption diffusion coefficient of mosiure-equilibrate sample is lower than that of dried coal sample. Liquid water in water injection sample wets coal surface and forms water film, and the medium viscosity of water injection sample is close to that of moisture-equilibrated sample. However, the interaction force of wetted coal matrix and water film of water injection sample is higher than the force of moisture-equilibrated sample, which leads to the adsorption diffusion rate of water injection sample higher than that of moisture-equilibrate sample but lower than diffusion rate of dried coal sample.Like all models, Langmuir and Dubinin-Radushkevich have their own hypothesis conditions which make them can be applied in different reservoir pressure ranges and different type coal samples. For low rank moisture-equilibrated and water injection sample, the adaptability of Dubinin-Radushkevich model is greater than that of Langmuir model because Dubinin-Radushkevich model can be applied in wider reservoir pressure range. However, for middle or high rank moisture-equilibrated and water injection sample, the adaptability of Langmuir moedel is greater than that of Dubinin-Radushkevich model for the fitting degree of Langmuir moedel is higher than that of Dubinin-Radushkevich model.更多还原