Advances in low salinity waterflooding in China: performance, influencing factors, mechanisms, and hybrid methods

Low salinity waterflooding (LSWF) has emerged as a cost-effective and environmentally favorable enhanced oil recovery (EOR) technique, attracting extensive research attention worldwide. Various reviews existing in the literature systematically summarize the progress of LSWF, but with a focus on reservoirs outside China. Given the distinct geological characteristics, reservoir heterogeneity, crude oil compositions, and formation water chemistries of Chinese oilfields, a comprehensive and region-specific comprehensive review is still lacking. Here, we present a critical review of current studies on LSWF conducted in China, synthesizing laboratory investigations, numerical simulations, and theoretical analysis. This review is divided into four sections. First, the EOR performance of LSWF in different reservoir types (i.e., sandstone, carbonate, and unconventional oil reservoirs) in China is discussed. Second, important factors affecting LSWF performance, such as salinity, ion types, rock mineral content, oil properties, and reservoir conditions, are analyzed. Third, the fundamental mechanisms proposed to explain LSWF in Chinese reservoirs, including fines migration, wettability alteration, double layer expansion, multicomponent ion exchange, and pH-related effects, are critically discussed. Finally, recent advances in hybrid LSWF technologies combined with other EOR methods, such as chemical flooding, gas injection, and nanofluids, are reviewed. This article provides a detailed literature review to understand the status, challenges, and future research directions of LSWF in China, aiming to support more effective design and field implementation.