Comparative study on the volumetric and gravimetric method for isothermal adsorption experiment of shale

doi:10.16085/j.issn.1000-6613.2017.05.018

Abstract

Abstract: Shale gas content is one key parameter to accurately evaluate the gas content and the resource potentiality of shale gas reservoir,and it is usually determined by isothermal adsorption experiments which mainly include volumetric method and gravimetric method. The volumetric method is commonly used in isothermal adsorption experiments,but the application of the gravimetric method is rarely. The adsorption capacities tested by volumetric and gravimetric method are excess adsorption,and the absolute adsorption can't be directly tested by experiments. And then the conversion relationship of the excess absorption and absolute adsorption is established. In order to compare the accuracy and stability of the two methods,the two isothermal adsorption experiments of same sample are performed respectively. The test results show that the adsorption curve is a type I adsorption curve at low pressure,but when the pressure is further increased,the isothermal adsorption curve will decrease. There is an inevitable downward trend of the isothermal adsorption curve at high pressure,which is not an abnormal phenomenon,but is the essential characteristic of excess adsorption capacity of supercritical methane. Comparative analysis show that the isothermal adsorption experiment based on the gravimetric method is less sensitive to experimental environment and parameters than the volumetric method. Especially for shale of lower adsorption capacity,the error caused by the volumetric method is greater than the gravimetric method. Under the existing technical level,the gravimetric method is more suitable for the isothermal adsorption experiment of shale.

Key words: shale gas, volumetric method, gravimetric method, isothermal adsorption, excess adsorption

摘要： 页岩吸附气含量是准确评价页岩含气量和资源潜力的关键参数，目前通常采用等温吸附实验来确定。等温吸附实验方法主要分为容量法和重量法，容量法是目前常用的等温吸附实验方法，重量法的应用还较少。本文通过分析两种方法的实验原理，认为容量法和重量法等温吸附实验测得的吸附量均为过剩吸附量，绝对吸附量并不能通过实验直接测得，并建立了过剩吸附量与绝对吸附量的转换关系。为了对比分析两种实验方法的准确性和稳定性，分别进行了相同样品的容量法和重量法等温吸附实验。测试结果表明，低压时甲烷在页岩中的吸附曲线呈Ⅰ型的吸附曲线特征，但是当压力进一步增大后，等温吸附曲线会出现下降。页岩中超临界甲烷的等温吸附曲线在压力较大时，必然存在下降的趋势，这并非异常现象，而是超临界流体过剩吸附量的本质特征。对比分析认为，在传感器精度和天平精度经过校准的情况下，重量法等温吸附实验对实验参数和环境的敏感程度要低于容量法。特别是对于吸附量较低的泥页岩，容量法测试中引起的误差大于重量法。在现有技术水平条件下，认为重量法更适用于页岩的等温吸附实验研究。

关键词: 页岩气, 容量法, 重量法, 等温吸附, 过剩吸附量

CLC Number:

TE133

ZHOU Shangwen, LI Qi, XUE Huaqing, GUO Wei, LI Xiaobo, LU Bin. Comparative study on the volumetric and gravimetric method for isothermal adsorption experiment of shale[J]. Chemical Industry and Engineering Progress, 2017, 36(05): 1690-1697.

周尚文, 李奇, 薛华庆, 郭伟, 李晓波, 卢斌. 页岩容量法和重量法等温吸附实验对比研究[J]. 化工进展, 2017, 36(05): 1690-1697.

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