Dispersion Stability and Oil Displacement Effect of Modified Black Nanosheet

As an oil displacement system for oil reservoir in-depth conformance control, the black nanosheet (BN) can fully play the role of reducing oil–water interfacial tension, emulsifying crude oil, and changing rock wettability. However, at present, the dispersion stability of BNs is poor, and aggregation is prone to occur, which leads to the aggregation and sedimentation of BNs before pumping, affecting their injection and oil displacement performance. This study used a fine organic synthesis method to prepare a modified BN. The stability performance of the BN in low salinity water was analyzed by using a multiple light stabilizer and zeta potential analyzer. A displacement device was employed to conduct oil displacement experiments on BNs before and after modification and to compare their oil displacement effects. Results showed that modified BNs with good stability can be prepared from BNs, cetyltrimethylammonium bromide, and urea. Transmission electron microscopy testing showed that the modified BN had a black powder flake structure of 70 × 400 nm, which indicated the potential for application in low-permeability oil reservoir oil recovery. The modified BN introduced cationic hydrophilic groups and alkyl long chains, increasing the absolute zeta potential from 11.10 to 13.50 mV. The thermal stability index value measured by multiple light scattering confirmed a significant improvement in its stability from a microscopic perspective. Compared with unmodified BNs, modified BNs can significantly increase the oil recovery degree, with an increase of 12.51 percentage points. The modified BNs developed in this work had good dispersion stability and a high oil displacement effect, which could provide a new chemical system for efficient development of low-permeability reservoirs.