二氧化碳驱替页岩气的机理研究

发布时间：2018-05-20 14:32

本文选题：页岩岩芯 + 页岩气　；参考：《重庆大学》2015年硕士论文

【摘要】：已有很多学者对页岩的吸附、解吸及驱替进行研究并取得相应成果,对未来页岩气开采具有巨大的实用价值。但以往有关页岩的吸附、解吸及驱替试验采用的样品为颗粒状,严重破坏了页岩原始结构,无法真实地反映实际储层情况。为真实反映储层条件下的页岩吸附、解吸及驱替性能,本文试验中采用直径50mm,高100mm的大岩样页岩并对其施加一定的体积应力,岩样内保持页岩原始地质结构,与颗粒状页岩相比,能真实模拟储层结构条件。在国家自然科学基金面上项目(项目批准号:51374257)、教育部新世纪人才计划项目(项目批准号:NCET-09-0844)资助下,针对储层条件下页岩的吸附解吸性质及驱替提高页岩气采收率的部分影响因素开展了研究,取得以下主要研究成果:①本次试验样品为圆柱形页岩岩芯,为块状,其内部保持页岩储层原始结构,试验时对岩心施加一定的轴压和围压,并采用水浴方式恒温,以模拟相应页岩储层环境,确保试验能更为真实地反映页岩储层吸附、解吸、驱替性质。②基于大量室内页岩岩芯吸附过程试验,详细分析了甲烷和二氧化碳在页岩岩芯内运移、吸附过程,认为吸附过程为渗透、扩散、吸附、解吸的综合过程;解释了随时间推移,吸附速率下降的原因,主要是吸附前期以渗透、吸附为主,后期以扩散、吸附为主,气体在页岩储层内渗透作用相对扩散作用要快很多;详细分析了页岩岩芯在吸附过程中吸附变化曲线出现“阶梯状”、“负吸附”现象,认为出现上述现象是由于吸附量增大导致岩芯内部孔隙结构发生变化的结果。③通过对不同温度、不同页岩岩芯对甲烷的等温吸附曲线对比,发现这些曲线变化趋势相同,吸附量随压力升高而增大,且在相应压力点出现吸附量急剧上升的现象,这种现象出现的压力点随温度升高而增大;通过对页岩岩芯吸附、解吸曲线对比分析,发现岩芯解吸曲线滞后于吸附曲线,并从甲烷在页岩储层内赋存形式、吸附形式和分子能量三个方面对这一现象进行了详细分析。④通过对同一页岩岩芯样品不同温度下等温吸附曲线对比分析,探讨温度对吸附的影响,发现温度与吸附量相关性较差,并对此现象进行详细分析,认为岩芯在吸附膨胀、解吸收缩循环作用及体积应力共同作用下,页岩内部结构发生变化导致吸附量变化,表明保留页岩原始结构的岩芯的吸附性能受多种因素的影响,与颗粒状相比,吸附性质更具不稳定性。⑤通过对不同页岩岩芯样品在相同温度下的等温吸附曲线的对比分析,探讨页岩储层各向异性对吸附的影响,发现不同样品的吸附量不同;对同一样品进行不同气体(CH4、CO2)吸附试验对比分析,发现吸附相同时间,CO2的吸附量大于CH4,且CH4的吸附平衡时压力大于CO2,由此判断页岩岩芯对CO2的吸附性大于CH4。⑥将本次页岩岩芯吸附试验结果与相同试验温度下煤颗粒、页岩颗粒及页岩小试件吸附结果进行对比分析,并从岩石结构方面详细分析了吸附量差异及吸附曲线形态不同的原因,表明页岩试验样品尺寸对其吸附能力影响较大,认为随试件尺寸增大,页岩储层不均匀性越明显,越能真实模拟储层条件。⑦采用Langmuir模型、Freundlich经验公式、BET模型、微孔填充D-R模型、Langmuir-Freundlich模型和最优化体积填充D-A模型对本次吸附解吸试验数据进行拟合分析对比,探讨页岩岩芯对甲烷的吸附机理,拟合结果表明:Freundlich经验公式相关系数平均值为0.95635;D-R模型相关系数平均值为0.96559;D-A模型相关系数平均值为0.97963,以上三种模型拟合效果较好,其中Freundlich经验公式中参数物理意义不明确,不能表征吸附机理,由此认为甲烷在页岩岩芯内的吸附机理主要为微孔填充或体积填充。⑧基于页岩岩芯驱替试验数据,并对岩芯驱替过程机理进行了详细的分析和阐述,认为驱替是渗透、扩散、竞争吸附的综合过程;对不同温度、驱替方式的驱替结果进行对比,发现温度、驱替方式对驱替效果有影响,且驱替方式影响较大;对不同体积应力下的驱替结果对比分析,发现体积应力对驱替效果几乎不影响;对置换比的计算进行讨论,并阐述了新的计算思法,使该参数更能准确的表征CO2的驱替能力。
[Abstract]:Many scholars have studied shale adsorption, desorption and displacement and obtained corresponding results, which have great practical value for shale gas mining in the future. However, the previous shale adsorption, desorption and displacement tests were granular, which seriously damaged the original shale structure and could not truly reflect the actual reservoir conditions. Shale adsorption, desorption and displacement performance under reservoir conditions are reflected. In this experiment, the large rock sample shale with a diameter of 50mm, high 100mm, and a certain volume stress was applied to it, and the original geological structure of shale was maintained in the rock sample. Compared with the granular shale, the reservoir structure conditions could be simulated. Item approval number: 51374257), under the support of the new century talent planning project of the Ministry of Education (project approval number: NCET-09-0844), the study has been carried out on the adsorption and desorption properties of shale under reservoir conditions and some factors affecting shale gas recovery, and the following main research results are obtained: (1) the sample is cylindrical shale core. It maintains the original structure of shale reservoir in the interior of the shale, exerting certain axial pressure and confining pressure on the core in test, and using water bath at constant temperature to simulate the corresponding shale reservoir environment, to ensure that the test can more truly reflect the adsorption, desorption and displacement properties of shale reservoir. When methane and carbon dioxide are transported and adsorbed in shale core, the adsorption process is considered as a comprehensive process of infiltration, diffusion, adsorption and desorption. The reasons for the decrease of adsorption rate are explained with the passage of time, mainly by infiltration, adsorption, diffusion and adsorption, and the relative expansion of gas in shale reservoir. The effect of dispersion is much faster; the phenomenon of "staircase" and "negative adsorption" in the adsorption curve of shale core during the adsorption process is analyzed in detail. It is believed that the above phenomenon is the result of the change of pore structure inside the core caused by the increase of adsorption quantity. It is found that the changing trend of these curves is the same, the adsorption amount increases with the pressure increasing, and the adsorption quantity rises sharply at the corresponding pressure point. The pressure point of this phenomenon increases with the temperature rising. The occurrence of methane in shale reservoir, adsorption form and molecular energy in three aspects are analyzed in detail. (4) the effect of temperature on adsorption is discussed by comparison and analysis of isothermal adsorption curves at different temperatures of the same shale core samples, and it is found that the correlation between temperature and adsorption quantity is poor, and the phenomenon is analyzed in detail. Under the joint action of adsorption expansion, desorption contraction cycle and volume stress, the core structure changes in shale, which results in the change of adsorption capacity. It shows that the adsorption property of the core with the original structure of shale is influenced by many factors. Compared with the granular, the adsorbability is more unstable. The isothermal adsorption curves at the same temperature are compared and analyzed to explore the effect of anisotropy on adsorption of shale reservoir, and the adsorption capacity of different samples is different. The adsorption test of different gases (CH4, CO2) for the same sample is compared and analyzed. It is found that the adsorption amount of CO2 is greater than that of CH4 at the same time of adsorption, and the pressure of CH4 is more than CO when the adsorption equilibrium is balanced. 2, it is judged that the adsorption of shale core to CO2 is greater than that of CH4. 6. The adsorption results of the shale core adsorption test and the coal particles, shale particles and shale specimens are compared with the same test temperature, and the reasons for the difference of adsorption quantity and the different adsorption curve form are analyzed in detail. The sample size has a great influence on its adsorption capacity. It is considered that the larger the size of the specimen is, the more obvious the shale reservoir inhomogeneity is, the more true the reservoir conditions are, the Langmuir model, the Freundlich empirical formula, the BET model, the microporous filling D-R model, the Langmuir-Freundlich mold type and the optimal volume filling D-A model are used for this adsorption desorption. The experimental data are compared and analyzed to discuss the adsorption mechanism of methane in shale core. The fitting results show that the average value of correlation coefficient of Freundlich empirical formula is 0.95635, the average value of D-R model correlation coefficient is 0.96559, and the average value of D-A model correlation coefficient is 0.97963, and the above three models have better fitting effect, of which Freundlich experience male is more common. The physical meaning of the parameters is not clear, and the mechanism of adsorption can not be characterized. Therefore, the adsorption mechanism of methane in shale core is mainly microporous filling or volume filling. By comparing the displacement results of different temperatures and displacement ways, it is found that the displacement effect is influenced by the temperature and displacement mode, and the displacement mode has great influence. The displacement results under different volume stress are compared and analyzed, and the displacement effect is almost no sound. The calculation of displacement ratio is discussed and the new method is expounded. Calculating the method of thinking can make the parameter more accurately represent the displacement ability of CO2.
【学位授予单位】：重庆大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TE377

【相似文献】