Lu Guanwen, Wei Chongtao, Wang Jilin, Meng Ruiyan, Tamehe Landry Soh
Key Laboratory of Coalbed Methane Resource & Reservoir Formation Process (China University of Mining & Technology), Ministry of Education, Xuzhou 221008, China.
Jiangsu Design Institute of Geology for Mineral Resources, Xuzhou 221006, China.
ACS Omega. 2020 Jun 12;5(24):14597-14610. doi: 10.1021/acsomega.0c01286. eCollection 2020 Jun 23.
Adsorption reduction occurring during isothermal experiment leads to the failure of telling the true adsorption capacity of shale reservoir. A correct understanding of this will be helpful in improving the accuracy of resource estimation and economic evaluation of shale gas reserves. Six shale samples were collected from the Permian Longtan Formation in the western Guizhou Province, China. Volumetric methane isotherm adsorption experiment and data processing were conducted in this research. The study investigates the effect of free space volume reduction (FSVR), excess adsorption amount conversion (EAAC), and blank test correction (BTC) on adsorption reduction, the understanding of the dynamic process of adsorption reduction, and the evaluation of the way of weakening and correcting this phenomenon. The conclusions are as follows. (1) Adsorption reduction does exist in the shale sample. The adsorption process of methane in the shale sample can be divided into the strong adsorption stage, approximate saturation stage, and adsorption reduction stage. (2) Shale adsorbing methane has a positive effect on the experimental adsorption amount. Comparatively, free space volume, excess adsorption amount, and blank test have negative effects. Adsorption reduction is the result of combined influence of positive and negative effects above. (3) At the first two stages of methane adsorption, the positive effect is greater than the negative effect, resulting in the hidden of adsorption reduction, and the experimental adsorption amount increases with the growth of experimental pressure. While at the adsorption reduction stage, the former effect is smaller than the latter, and their difference increases as the experimental pressure increases. It leads to the occurrence of adsorption reduction, and the phenomenon becomes increasingly obvious. (4) FSVR has the strongest impact on the weakening of adsorption reduction, followed by EAAC and BTC. The adsorption reduction in shale reservoir can be corrected effectively by BTC and EAAC.
等温实验过程中发生的吸附量减少会导致无法准确获知页岩储层的真实吸附能力。正确认识这一点将有助于提高页岩气储量资源估算和经济评价的准确性。从中国贵州省西部二叠系龙潭组采集了六个页岩样品。本研究进行了体积法甲烷等温吸附实验及数据处理。该研究考察了自由空间体积减小（FSVR）、过量吸附量转换（EAAC）和空白试验校正（BTC）对吸附量减少的影响，对吸附量减少动态过程的认识，以及对弱化和校正该现象方法的评估。结论如下：（1）页岩样品中确实存在吸附量减少现象。页岩样品中甲烷的吸附过程可分为强吸附阶段、近似饱和阶段和吸附量减少阶段。（2）页岩吸附甲烷对实验吸附量有正向影响。相比之下，自由空间体积、过量吸附量和空白试验有负向影响。吸附量减少是上述正负效应共同作用的结果。（3）在甲烷吸附的前两个阶段，正向效应大于负向效应，导致吸附量减少被掩盖，实验吸附量随实验压力的增加而增大。而在吸附量减少阶段，前者效应小于后者，且二者差值随实验压力增加而增大。这导致吸附量减少现象的发生，且该现象愈发明显。（4）FSVR对吸附量减少的弱化影响最强，其次是EAAC和BTC。BTC和EAAC可有效校正页岩储层中的吸附量减少现象。
