Characterization of methane adsorption on shale and isolated kerogen from the Sichuan Basin under pressure up to 60 MPa: Experimental results and geological implications
Characterization of methane adsorption on shale and isolated kerogen from the Sichuan Basin under pressure up to 60 MPa: Experimental results and geological implications
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DOI：
10.1016/j.coal.2018.02.020
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发表时间：
2018-03-15
影响因子：
5.6
通讯作者：
Zhang, Yuhong
中科院分区：
文献类型：
--
作者：
Li, Jing;Zhou, Shixin;Zhang, Yuhong
测定了四川盆地古生代干燥、过成熟页岩和分离干酪根在孔压高达60 Mpa、60℃、100℃和140℃下的甲烷吸附等温线。测得的超额吸附量随压力的增加而增加，在压力为8~18 Mpa时达到最大值，然后减小。在18~60 Mpa范围内，随着压力的增加，降幅减小，归因于游离态甲烷密度随压力的非线性增加。此外，在48~60兆帕的压力下，超额吸附也有异常的增加。基于超临界Dubinin-Radushkevich(SDR)的超额吸附模型和基于Langmuir的超额吸附模型都能很好地代表超额吸附等温线。在0~30 Mpa的原始数据下，拟合的最大绝对吸附容量比0~60 Mpa的原始数据平均大11.5%。这一偏差表明，实验得出的气体吸附特性可能会相对于各自实验中使用的最大孔压产生偏差。在焦石坝页岩气藏主要页岩地层的现场静水压力和温度条件下，干酪根对所研究的古生界页岩样品的甲烷总吸附容量的贡献均小于50%。然而，在现实的地质条件下，这种贡献应该更大，特别是因为存在的水分会比有机质对粘土的影响更大，从而降低粘土对总吸附能力的贡献。胶石坝页岩气田主要页岩地层在地质静水压力和温度条件下的GIP估算为5.36~6.64 cm(3)/g。
A series of methane adsorption isotherms were measured at pore pressures up to 60 MPa and at 60 degrees C, 100 degrees C and 140 degrees C for dried and overmature Paleozoic shales and isolated kerogen from the Sichuan Basin. At first, the measured excess adsorption increases with increasing pressure, reaches a maximum value at pressures ranging between 8 and 18 MPa and then decreases. The rate of decrease reduces with increasing pressures from 18 to 60 MPa, which is attributed to the nonlinear increase of free methane density with pressure. Additionally, an unusual increase of excess adsorption at pressures from 48 to 60 MPa was observed. Both, the supercritical Dubinin-Radushkevich (SDR)-based and Langmuir-based excess adsorption models, represent the excess adsorption isotherms equally well. The fitted maximum absolute adsorption capacities, when based on raw data from 0 to 30 MPa, are larger by an average of 11.5% when compared to the raw data from 0 to 60 MPa. This deviation indicates that experimentally derived gas adsorption characteristics can be biased with respect to the maximum pore pressure used in the respective experiments. The kerogen contribution to the total methane adsorption capacity of studied Paleozoic shale samples under in-situ hydrostatic pressure and temperature conditions of main shale formations in the Jiaoshiba shale gas play is lower than 50%. However, this contribution should be larger under realistic geological conditions, especially as existent moisture will affect clays stronger than organic matter and therefore reduce the contribution of clay towards the total sorption capacity. The estimated GIP of Paleozoic shales under geological hydrostatic pressure and temperature conditions of main shale formations in the Jiaoshiba shale gas play is 5.36-6.64 cm(3)/g.