Characterization of methane adsorption on overmature Lower Silurian-Upper Ordovician shales in Sichuan Basin, southwest China: Experimental results and geological implications
Characterization of methane adsorption on overmature Lower Silurian-Upper Ordovician shales in Sichuan Basin, southwest China: Experimental results and geological implications
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DOI：
10.1016/j.coal.2016.01.013
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发表时间：
2016-02
影响因子：
5.6
通讯作者：
H. Tian;Tengfei Li;Tongwei Zhang;X. Xiao
中科院分区：
文献类型：
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作者：
H. Tian;Tengfei Li;Tongwei Zhang;X. Xiao
在35.4 °C、50.6 °C和65.4 °C、15.0 MPa的压力下，测定了四川盆地下志留统-上奥陶统8个过成熟页岩样品的甲烷吸附等温线，其TOC值在1.87- 5.74%之间。在65.4 °C时测得的甲烷过量吸附容量的最大值范围为1.25至2.50 cm 3/g岩石;在35.4 °C时最大值略有增加，但都与总有机碳（TOC）呈正相关。这两个超临界Dubininin-Radushkevich（SDR）-和朗缪尔为基础的过量吸附模型被发现代表的实验过量吸附等温线同样在实验范围内。由基于SDR的过量吸附模型的参数拟合得到的甲烷吸附密度随温度的变化范围为297-415 mg/cm 3;对于基于Langmuir的过量吸附模型，调整后的密度范围为386 - 1027 mg/cm 3，其中大部分远大于甲烷在其沸点下的液体密度（424 mg/cm 3）。然而，两种模型拟合的甲烷绝对吸附量的最大值没有显着差异，并呈线性相关。造成地质条件下天然气储量估计不确定性的原因之一是，将实验过量吸附数据用作“绝对吸附”值的做法不一致，特别是在高压下。然而，选择吸附模型本身（朗缪尔或SDR为基础的）和拟合程序，假设恒定或温度依赖性的吸附相密度和最大吸附容量，不显着影响估计GIPs的地质系统在这里研究的深度小于4000米。
A series of methane adsorption isotherms were measured at 35.4 °C, 50.6 °C, and 65.4 °C at pressures up to 15.0 MPa for eight dried, overmature Lower Silurian–Upper Ordovician shale samples collected from the Sichuan Basin with TOC values in the range of 1.87–5.74%. The measured maxima of excess adsorption capacity of methane range from 1.25 to 2.50 cm3/g rock at 65.4 °C; the maxima are slightly enhanced at 35.4 °C, but all are positively correlated with total organic carbon (TOC). Both the supercritical Dubinin–Radushkevich (SDR)- and Langmuir-based excess adsorption models were found to represent the experimental excess adsorption isotherms equally well within the experimental range. The temperature-dependent densities of adsorbed methane resulting from the parameter fit of the SDR-based excess adsorption model are in the range of 297–415 mg/cm3; for the Langmuir-based excess adsorption model, the adjusted densities range from 386 mg/cm3to 1027 mg/cm3and most of them are much larger than the liquid density of methane at its boiling point (424 mg/cm3). Nevertheless, the maxima of absolute methane adsorption capacity fitted by both models are not significantly different and are linearly correlated. One of the contributors to the uncertainty of the gas-in-place estimation in geological conditions is the inconsistent utilization of experimental excess sorption data as “absolute sorption” values, particularly at high pressures. However, the choice of adsorption model itself (Langmuir- or SDR-based) and the fitting procedure, assuming either constant or temperature-dependent adsorbed phase density and maximum sorption capacity, do not significantly affect the estimated GIPs for the geological system studied here with depths of less than 4000 m.