Comprehensive Treatment and Optimization of Lake Water and Produced Water for Low Salinity Water Flooding in Enhanced Oil Recovery

: This investigation evaluates the suitability of treated lake water (LW) for injection and as a diluent for produced water (PW) in low-salinity enhanced oil recovery (EOR), revealing through comprehensive characterization that excessive TSS, turbidity, poor filterability, elevated dissolved oxygen, scaling and corrosion tendencies, and microbial activity in both waters induce adverse physico-chemical interactions in the crude oil–water system that could impair oil recovery efficiency. A treatment protocol was formulated, incorporating coagulation–flocculation with 80 ppm polyaluminum chloride (PAC) and 2 ppm polyacrylamide (PAM), two-stage filtration (20–25 μm followed by 5 μm), mechanical deaeration with sodium bisulfite scavenging, and PBTC-based corrosion/scale control. Microbial control was implemented through initial chlorination and alternating slug doses of THPS and glutaraldehyde. Filtration and core flood experiments validated superior injectivity, with permeability retention exceeding 88% when using 5 μm and 2.5 μm filters. Dilution experiments involving produced water and lake water mixtures demonstrated that an increased proportion of lake water corresponded with a more negative zeta potential. This observation suggests an expansion of the electrical double layer and enhanced colloidal stability, both of which are associated with decreased salinity. The PW (20%) + LW (80%) mixture exhibited the lowest interfacial tension (14.9 mN/m) and contact angle (61.6°), thereby indicating more water-wet conditions that are conducive to oil mobilization. Consequently, the optimum composition yielded an additional recovery of 6.3% OOIP in tertiary mode during coreflooding experiments. The findings indicate that appropriately treated lake water can fulfil injection quality standards and, when utilised to dilute produced water, improve wettability alteration and displacement efficiency, thereby underscoring its considerable potential for sustainable low-salinity EOR applications.