Combined imbibition system with black nanosheet and low-salinity water for improving oil recovery in tight sandstone reservoirs

Nanomaterials and low-salinity water (LSW) are two popular enhanced oil recovery (EOR) methods that have been widely studied in recent years. The former is used for in-depth conformance improvement and the latter for microscopic oil displacement (by altering the potential and contact angle). However, there are few literature on combining them to achieve synergistic effects, especially for tight sandstone reservoirs. Based on the reservoir conditions of the Jimusar Oilfield, this study investigated the oil recovery mechanism of the combined imbibition system, which was composed of black nanosheet (BN) and LSW. Its performances including decreasing interfacial tension, emulsification, and wettability alterations were evaluated. The imbibition differences between the single system of BN and LSW and the combined BN-LSW imbibition system were then compared. Results showed that the combined imbibition system had a better emulsification effect on the crude oil and could also alter the wettability of the core surface. Moreover, the combined system could increase both the imbibition rate and the ultimate oil recovery. The nuclear magnetic T₂ spectrum also indicated that the addition of black nanosheets could divert more fluid into small pores and thus improve the microscopic sweep efficiency.