Montmorillonite swelling properties with various surfactants based on molecular simulation

The clay swelling is extremely harmful to the reservoir during tight oil and shale oil extraction. In order to prevent the interaction between clay and surfactants from making the clay to hurt reservoir during oil recovery, this paper studies the effects of different surfactants on reservoir clay. Clay-surfactant swelling experiments were conducted to observe the macroscopic effects of different surfactants on clay swelling and to summarize the rules, and molecular simulations were then used to explain this phenomenon. The results show that different surfactant groups have different tendencies to move toward the clay in water, with cationic groups moving toward the montmorillonite layers and anionic groups moving away from the montmorillonite layers, and nonionic does not have a significant effect. Cationic surfactant and amphoteric surfactant whose mechanism of inhibiting swelling action is directly reducing the negative electrical properties of the montmorillonite layers when Na+ outflow from montmorillonite layers, thus preventing electrostatic repulsion between montmorillonite layers to repel each other and move far away. In contrast, the nonionic surfactant, because it is not charged, cannot prevent the hydration of montmorillonite although there are surfactant molecules adsorbed on the layers due to van der Waals force; and the addition of anionic surfactant cannot suppress the negative electrical properties between the layers, which makes the diffusion of sodium ions between the layers augmented and promotes the swelling and dispersion of montmorillonite. This study is expected to provide benefits to oil production area by reducing the damage of surfactant imbibition fluid.