Abstract Accurate description of absolute adsorption/desorption behavior for hydrocarbons on shale is of critical importance to the understanding of the fundamental mechanisms governing the storage, transport, and recovery of shale gas or shale gas condensate in shale reservoirs. By applying a thermogravimetric method, we first measure the excess adsorption/desorption isotherms of pure CH 4 and n -C 4 H 10 on shale samples over the temperature range of 303.15–393.15 K. The maximum test pressures considered for CH 4 and n -C 4 H 10 are 50 bar and 2 bar, respectively. Grand Canonical Monte Carlo (GCMC) simulations are then applied to calculate the density of the adsorption phase by considering the fluid-pore surface interactions. We use such calculated density of the adsorption phase to calibrate the excess adsorption/desorption isotherms, which enables us to eventually obtain the absolute adsorption/desorption isotherms. Such approach for estimating the density of the adsorption phase is essentially different from the commonly used approaches in which the density of the adsorption phase is considered to be independent of temperature, pressure, and pore size. The adsorption/desorption test results show that both CH 4 and n -C 4 H 10 exhibit more adsorption as temperature decreases or pressure increases. Their adsorption/desorption isotherms exhibit hysteresis phenomenon and this phenomenon weakens as temperature increases. Comparatively, the hysteresis behavior observed for n -C 4 H 10 is more obvious than that for CH 4 . Compared with CH 4 , n -C 4 H 10 has higher adsorption capacity under the same condition , indicating its higher affinity towards the shale with organic matters. As for the conventional approaches, the density calculated from the van der Waals constant b or the liquid hydrocarbon density can be used to reasonably well evaluate the absolute adsorption isotherms of n -C 4 H 10 on shale, but tends to underestimate the absolute adsorption of CH 4 on shale. GCMC simulations show that the density of the adsorption phase is strongly correlated with system pressure, temperature, and pore size. Compared to the conventional approaches, GCMC simulations can better capture the in-situ density of adsorption phase; on the basis of the in-situ density of adsorption phase, we can then achieve more accurate determination of the absolute adsorption isotherms of a given hydrocarbon on shale. This study raises the imperativeness of leveraging more sophisticated simulation tools (such as GCMC) for more accurate determination of absolute adsorption isotherms.

中文翻译：

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从纳米尺度确定页岩上 CH 4 和 n -C 4 H 10 的绝对吸附/解吸等温线

摘要 准确描述页岩上烃类的绝对吸附/解吸行为对于理解控制页岩气或页岩气凝析油储层储运和采收的基本机制至关重要。通过应用热重法，我们首先测量了页岩样品在 303.15–393.15 K 温度范围内的纯 CH 4 和 n -C 4 H 10 的过量吸附/解吸等温线。CH 4 和 n - 考虑的最大测试压力C 4 H 10 分别为50巴和2巴。然后应用 Grand Canonical Monte Carlo (GCMC) 模拟通过考虑流体-孔隙表面相互作用来计算吸附相的密度。我们使用这样计算出的吸附相密度来校准过量吸附/解吸等温线，这使我们能够最终获得绝对吸附/解吸等温线。这种估计吸附相密度的方法与通常使用的吸附相密度被认为与温度、压力和孔径无关的方法有本质的区别。吸附/解吸测试结果表明，随着温度降低或压力增加，CH 4 和n -C 4 H 10 都表现出更多的吸附。它们的吸附/解吸等温线表现出滞后现象，这种现象随着温度的升高而减弱。相比之下，n -C 4 H 10 的滞后行为比CH 4 的滞后行为更明显。与CH 4 相比，n -C 4 H 10 在相同条件下具有更高的吸附容量，表明其对有机质页岩具有更高的亲和力。对于常规方法，由范德华常数 b 计算的密度或液态烃密度可以很好地评估页岩上 n -C 4 H 10 的绝对吸附等温线，但往往低估了绝对吸附页岩上的 CH 4。GCMC 模拟表明吸附相的密度与系统压力、温度和孔径密切相关。与传统方法相比，GCMC 模拟可以更好地捕捉吸附相的原位密度；根据吸附相的原位密度，我们可以更准确地确定给定烃在页岩上的绝对吸附等温线。