Key Laboratory of Continental Shale Hydrocarbon Accumulation and Efficient Development, Ministry of Education, Northeast Petroleum University, Daqing 163318, China.
Institute of Unconventional Oil & Gas, Northeast Petroleum University, Daqing 163318, China.
Molecules. 2022 Jul 19;27(14):4590. doi: 10.3390/molecules27144590.
Hydrocarbon vapor adsorption experiments (HVAs) are one of the most prevalent methods used to evaluate the proportion of adsorbed state oil, critical in understanding the recoverable resources of shale oil. HVAs have some limitations, which cannot be directly used to evaluate the proportion of adsorbed state oil. The proportion of adsorbed state oil from HVA is always smaller than that in shale oil reservoirs, which is caused by the difference in adsorption characteristics of liquid and gaseous hydrocarbons. The results of HVA need to be corrected. In this paper, HVA was conducted with kaolinite, an important component of shale. A new method is reported here to evaluate the proportion of adsorbed state oil. Molecular dynamics simulations (MDs) of gaseous/liquid hydrocarbons with the same temperature and pressure as the HVAs were used as a reference to reveal the errors in the HVAs evaluation from the molecular scale. We determine the amount of free state of hydrocarbons by HVAs, and then calculate the proportion of adsorbed state oil by the liquid hydrocarbon MD simulation under the same conditions. The results show that gaseous hydrocarbons adsorptions are monolayer at low relative pressures and bilayer at high relative pressures. The liquid hydrocarbons adsorption is multilayer adsorption. The adsorption capacity of liquid hydrocarbons is over 2.7 times higher than gaseous hydrocarbons. The new method will be more effective and accurate to evaluate the proportion of adsorbed state oil.
烃类蒸汽吸附实验（HVAs）是评估吸附态油量的最常用方法之一，对于理解页岩油可采资源至关重要。HVAs 存在一些局限性，不能直接用于评估吸附态油的比例。由于液体和气态烃类吸附特性的差异，从 HVA 得到的吸附态油比例总是小于页岩油藏中的比例。需要对 HVA 的结果进行修正。本文对页岩的重要组成部分——高岭土进行了 HVA 实验。报告了一种新的方法来评估吸附态油的比例。使用与 HVAs 相同温度和压力的气态/液态烃的分子动力学模拟（MDs）作为参考，从分子尺度揭示 HVAs 评估中的误差。我们通过 HVAs 确定烃类的自由态量，然后在相同条件下通过液态烃 MD 模拟计算吸附态油的比例。结果表明，在低相对压力下，气态烃类吸附为单层，在高相对压力下为双层。液态烃类的吸附为多层吸附。液态烃类的吸附容量比气态烃类高 2.7 倍以上。这种新方法将更有效地评估吸附态油的比例，且更加准确。
