Black Nanosheet-Enhanced Low-Salinity Water System for Improving Oil Recovery in a Low-Permeability Conglomerate Reservoir
Daoyi Zhu, Junhui Qin, Yanyan Gao, Si Guo, Ling Bai, Yuheng Zhao, Qi Zhao, Hongjun Zhang
Abstract
Black nanosheets (BNs) and low-salinity water (LSW) flooding are two effective methods for improving oil recovery in low-permeability or ultra-low-permeability petroleum reservoirs. The former focuses on emulsification and interfacial tension reduction, while the latter focuses on wettability alteration. Combining BN with LSW is expected to achieve dual effects in oil recovery. However, there has been no research on the combination effect of BN and LSW on conglomerate reservoirs. Therefore, this study aims to investigate the oil imbibition mechanism of the BN–LSW composite system in the tight reservoir of Mahu Oilfield. The interfacial properties of the BN–LSW composite system were evaluated in terms of the oil–water interfacial tension, crude oil emulsification capability, and three-phase contact angle between oil, water, and rock. Through the imbibition experiment of the natural cores in Mahu Oilfield, the imbibition differences between single systems and the BN–LSW composite system were compared. The results showed that the BN–LSW composite system had minimal impact on the interfacial tension between oil and water compared to formation brine, LSW, and BN solution. However, the composite system demonstrated a significant emulsification effect with Mahu crude oil and alterated the wettability of the core. Compared to the single systems, the imbibition rate of the BN–LSW composite system was higher, resulting in an improved imbibition effect. The NMR T 2 signal explained the synergistic core imbibition effect of the BN–LSW composite system at the microscopic scale. The research outcomes of this study can provide a new approach for developing low-permeability and ultra-low-permeability reservoirs, holding practical value and reference significance.