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.