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Description
The exploitation of shale oil holds significant potential, making it essential to understand the occurrence and transport behavior of multicomponent alkanes through shale nanopores for enhanced oil recovery. However, current molecular simulations primarily focus on single-component alkane flow in shale nanopores, failing to capture the multicomponent nature of shale oil accurately. Moreover, existing simulations often employ unrealistically high driving pressures, which deviate from actual reservoir conditions.
To address these issues, we employed the Steered Molecular Dynamics (SMD) method to study the transport mechanisms of multicomponent alkanes within quartz nanopores of shale. We utilized a representative mixture of light components, including saturated and aromatic hydrocarbons, alongside heavy components such as resins and asphaltenes, to better characterize shale oil. We explored the heterogeneous distribution and differential flow behavior of the multicomponent alkanes. Initially, we applied spring forces to the alkanes and analyzed their molecular trajectories, density and velocity distributions, displacements, and interaction energies. We determined the threshold pressures for fluid flow across different layers and components within the nanopores, revealing the stratified occurrence of multicomponent fluids and differentiated flow patterns. Subsequently, we conducted a sensitivity analysis to assess the impacts of pore size, driving force, and molar ratios on the observed behaviors.
We reach the following conclusions: strong interactions between the pore walls and fluids create a higher threshold pressure for the fluid adjacent to the walls. In contrast, the fluid located in the central pore, which experiences less constraint, shows lower threshold pressure and improved mobility. The threshold pressures of different hydrocarbons follow this order: saturated hydrocarbons < aromatic hydrocarbons < resins < asphaltenes. Due to weaker interactions with the pore walls, lighter components exhibit higher diffusivity and better transport capabilities. Conversely, heavy components, influenced by strong wall interactions and internal cohesion, tend to aggregate and move more slowly. Increasing pore size has a minimal effect on the thickness of the adsorption layer but does increase the volume of free fluid, thereby enhancing fluid mobility. On the other hand, smaller pores, characterized by intense wall interactions, necessitate excessively high threshold pressures for fluid flow, making mobilization difficult. Heavy components can aggregate and form solid or semi-solid “kerogen-like” substances within the pores. An increase in the content of heavy components further deteriorates fluid mobility, allowing lighter components to escape only through gaps among the heavier hydrocarbons. As the driving force rises, heavy components gradually disperse, resulting in more heterogeneous fluid migration. Additionally, some fluid molecules may detach from the main flow and re-adsorb onto the walls.
This study provides a theoretical basis for optimizing shale oil development strategies and sheds light on the differential flow characteristics of multicomponents in nanopores and nanoporous media.
| Country | China |
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