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A developed dual-site Langmuir model to represent the high-pressure methane adsorption and thermodynamic parameters in shale
International Journal of Coal Science & Technology ( IF 6.9 ) Pub Date : 2023-10-01 , DOI: 10.1007/s40789-023-00629-x
Ke Hu , Qian Zhang , Yufei Liu , Muhammad Abdurrahman Thaika

Comprehending the mechanism of methane adsorption in shales is a crucial step towards optimizing the development of deep-buried shale gas. This is because the methane adsorbed in shale represents a significant proportion of the subsurface shale gas resource. To properly characterize the methane adsorption on shale, which exhibits diverse mineral compositions and multi-scale pore sizes, it is crucial to capture the energy heterogeneity of the adsorption sites. In this paper, a dual-site Langmuir model is proposed, which accounts for the temperature and pressure dependence of the density of the adsorbed phase. The model is applied to the isothermals of methane adsorption on shale, at pressures of up to 30 MPa and temperatures ranging from 40 to 100 °C. The results show that the proposed model can describe the adsorption behavior of methane on shale more accurately than conventional models, which assume a constant value for the density of adsorbed phase. Furthermore, the proposed model can be extrapolated to higher temperatures and pressures. Thermodynamic parameters were analyzed using correctly derived equations. The results indicate that the widely used, but incorrect, equation would underestimate the isosteric heat of adsorption. Neglecting the real gas behavior, volume of the adsorbed phase, and energy heterogeneity of the adsorption sites can lead to overestimation of the isosteric heat of adsorption. Furthermore, the isosteric heat evaluated from excess adsorption data can only be used to make a rough estimate of the real isosteric heat at very low pressure.



中文翻译:

开发的双点 Langmuir 模型来表示页岩中的高压甲烷吸附和热力学参数

理解页岩中甲烷吸附的机理是优化深层页岩气开发的关键一步。这是因为页岩中吸附的甲烷占地下页岩气资源的很大一部分。页岩具有多种矿物成分和多尺度孔径,为了正确表征页岩上的甲烷吸附,捕获吸附位点的能量异质性至关重要。在本文中,提出了双位点朗缪尔模型,该模型解释了吸附相密度的温度和压力依赖性。该模型适用于页岩上甲烷吸附的等温线,压力高达 30 MPa,温度范围为 40 至 100 °C。结果表明,与假设吸附相密度恒定值的传统模型相比,该模型能够更准确地描述甲烷在页岩上的吸附行为。此外,所提出的模型可以外推到更高的温度和压力。使用正确导出的方程分析热力学参数。结果表明,广泛使用但不正确的方程会低估等量吸附热。忽略真实的气体行为、吸附相的体积和吸附位点的能量异质性可能导致对吸附等量热的高估。此外,根据过量吸附数据评估的等量热只能用于粗略估计极低压力下的真实等量热。

更新日期:2023-10-03
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