页岩气超临界吸附的Dubibin-Astakhov改进模型

甲烷在页岩上的吸附属于物理吸附,且属于超临界吸附。利用Gibbs公式将过剩吸附量转换为绝对吸附量,将Dubibin-Astakhov(D-A)吸附模型和吸附特征曲线结合,研究了页岩中超临界甲烷的吸附机理。研究结果表明:D-A方程不能直接应用于页岩中甲烷吸附机理的研究,因为其得到的吸附特征能是温度的函数,与吸附势理论相违背;D-A吸附模型和吸附特征曲线结合,推导出了改进的D-A吸附模型,其中虚拟饱和蒸汽压的计算采用改进的Dubinin公式,同时利用提出的改进Amankwah方法求取最优k值;改进的D-A吸附模型能够预测页岩中甲烷的吸附等温线,且其精度较高,能够预测页岩储层不同温度、压力下甲烷在页岩中的吸附量,并可以用于页岩气资源评价。

Improved Dubibin-Astakhov model for shale-gas supercritical adsorption

Methane on shale is formed through physical adsorption, also belonging to supercritical adsorption. Gibbs equation was used to convert excess adsorption amount to absolute adsorption amount. Meanwhile, the adsorption mechanism of supercritical shale methane was studied using Dubibin-Astakhov (D-A) adsorption model in combination with adsorption characteristic curve. Research results show that D-A equation cannot be directly applied in researches of the adsorption mechanism of shale methane, because the obtained adsorption characteristic energy was expressed as the function of temperature, inconsistent with the adsorption potential theory. Therefore, the improved D-A adsorption model was derived from D-A adsorption model based on adsorption characteristic curve. The pseudo-saturation vapor pressure was calculated using the improved Dubinin equation, and simultaneously, the optimal k value was obtained by the improved Amankwah method. The improved D-A adsorption model could be used not only for predicting the adsorption isotherm of shale methane, and even the adsorption amount of shale methane under any temperature and pressure with high accuracy, but also for evaluating shale gas resources.