Abstract
Polymer flooding is a promising chemical enhanced oil recovery (EOR) method, which realizes more efficient extraction in porous formations characterized with nanoscale porosity and complicated interfaces. Understanding the molecular mechanism of viscoelastic polymer EOR in nanopores is of great significance for the advancement of oil exploitation. Using molecular dynamics simulations, we investigated the detailed process of a viscoelastic polymer displacing oil at the atomic scale. We found that the interactions between polymer chains and oil provide an additional pulling effect on extracting the residual oil trapped in dead-end nanopores, which plays a key role in increasing the oil displacement efficiency. Our results also demonstrate that the oil displacement ability of polymer can be reinforced with the increasing chain length and viscoelasticity. In particular, a polymer with longer chain length exhibits stronger elastic property, which enhances the foregoing pulling effect. These findings can help to enrich our understanding on the molecular mechanism of polymer enhanced oil recovery and provide guidance for oil extraction engineering.
Highlights
In order to meet the growing need for petroleum resources, there is an increasing demand to further improve oil recovery factors from mature fields which have already been exploited for years [1,2]
We used the injected pore volume (PV) to measure the accumulated flooding agent injection, which was defined as the ratio of the accumulated number of atoms flowing across the boundary in X direction to the total polymer atom number
We theoretically investigated the molecular mechanism of viscoelastic polymer enhanced oil recovery (EOR) in nanopores
Summary
In order to meet the growing need for petroleum resources, there is an increasing demand to further improve oil recovery factors from mature fields which have already been exploited for years [1,2]. A large amount of residual oil is still trapped in dead ends, which are unconnected zones in the pores, leading to a low oil recovery efficiency of water flooding [7,14]. As for the oil films attached to the rock surface, it is found that the velocity gradient near the wall for elastic fluids is considerably greater than that for Newtonian fluids, causing a stronger force to strip oil films off [29,30] Those previous efforts help one to understand the oil displacement mechanisms of polymer flooding. Oila–wall polymer–oil aOil means every type of atom in heptane, decane and toluene molecules
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