Mechanism of oil film stripping by active MoS2 nanosheets

Abstract

Nanomaterials for enhanced oil recovery （EOR） have gained more and more attention from petroleum researchers. However， the research mainly focuses on the properties of spherical nanomaterials， and the research on two-dimensional nanosheets is insufficient. In this paper， the amphiphilic MoS2 nanosheets （active MoS2 nanosheets） were independently synthesized to significantly enhance the oil recovery after water flooding in reservoirs. The spreading law of active MoS2 nanosheets on a solid surface was studied， and the mechanism of active MoS2 nanosheets on an oil film of a solid surface was elucidated. Based on the measurement of the gas-water-solid three-phase contact angle， it is determined that the equilibrium contact angles of water droplets remain unchanged at 90° after oil-wet quartz is immersed in an oil displacement system of active MoS2 nanosheets for 120 h. Eventually， the wettability of the quartz surface changes from oil-wet to neutral-wet. Both formation water and SiO2 nanofluid （mass fraction of 0.15%） fail to make the oil film produce wedge film on the solid surface. However， the oil displacement system of active MoS2 nanosheets （mass fraction of 0.005%） could form a prominent wedge film in the oil-water-solid three-phase contact area， then form structural disjoining pressure and eventually strip the oil film from the solid surface. Moreover， it is found that the oil film could form two contact lines （inner line and outer line） during the contraction process on the solid surface in the oil displacement system of active MoS2 nanosheets （mass fraction of 0.005%）. The contraction velocities of the inner contact line and the outer contact line are 0.661 7 × 10-5 and 8.581 7 × 10-5 cm/s， respectively. From the perspective of thermodynamics， the Gibbs free energy increment of the oil-water-solid mixture system is negative in the contraction process of oil film， which proves that the contraction of the oil film in the oil displacement system of MoS2 nanosheets is spontaneous. The research results show that the oil displacement system of MoS2 nanosheets （mass fraction of 0.005%） has high oil displacement efficiency.

Keywords

• active mos2 nanosheets
• structural disjoining pressure
• wettability
• gibbs free energy
• oil displacement efficiency