(3eh) Adsorption Behavior of Shale Oil in Slit Pores and Its Underlying Mechanisms: Insights from Molecular Dynamic Simulation

Research Interests: Shale Oil Adsorption

Shale oil development has attracted much attention from the world. However, the adsorption behavior and its underlying mechanism of shale oil is not yet well understood. It is imperative to investigate the adsorption behavior for enhancing shale oil recovery.

In this work, the effect of wettability, pressure, pore size, rock lithology and shale oil composition on the adsorption of shale oil was studied in slit pores. Firstly, the main composition of shale oil and shale oil properties were determined through PVT experiments. Secondly, the literature date of shale porous media was collected to determine main shale replacement model build surface, and then the shale surface was decorated for oil-wet and water-wet to explore the effect of wettability on shale oil adsorption. Thirdly, slit pore was established to study the influence of wettability, pore size and pressure on the adsorption of shale oil. Fourthly, the effect of different shale surface composition on the adsorption of shale oil was investigated. Finally, cycloalkanes, aromatic hydrocarbons and asphaltenes were added in different ratios to study the effect of shale oil composition on shale oil adsorption by keeping shale oil density constant during the process.

The adsorption energy, density distribution, and radial distribution function of shale oil were analyzed to get the shale oil adsorption mechanisms. Results show that shale oil will be preferentially adsorbed on the oil-wet surface, followed by the neutral one, and finally the water-wet surface. Meanwhile, the adsorption between shale oil and shale surface will be weakened with the increase of pore size and the decrease of pressure. Different shale compositions play an important role in affecting the adsorption of shale oil, the interaction between organic matter and shale oil being the weakest, this may cause differences in shale oil liquidity. Through the analysis of density distribution, we found that the interaction between the aromatic hydrocarbon and shale surface is greater than that of asphaltene, naphthene, and linear alkane.

In this work, the adsorption behavior and its underlying mechanism of shale oil under different conditions was characterized, which may provide theoretical guidance for revealing the change of shale oil distribution before and after fracturing and the mechanism of subsequent enhanced oil recovery.