Effect of pH on interfacial tension reduction of oil (Heavy acidic crude oil, resinous and asphaltenic synthetic oil)/low salinity solution prepared by chloride-based salts

Chloride salts of NaCl, KCl, CaCl2, and MgCl2 are among the essential salts examined for enhanced oil recovery (EOR) purposes through chemical injection, low salinity injection, smart water injection, etc. These salts are crucial for EOR studies since they exist in the reservoir with undeniable effects on interfacial tension (IFT), wettability alteration, etc. The alkaline injection that can produce in-situ soap leading to lower IFT values can be combined with low salinity injection method to form the hybrid EOR method. Among the different parameters in alkaline flooding, the aqueous solution pH is essential, since there is a strong relationship between the pH of the solution and crude oil type for ionization and generating in-situ soap. Whit this parameter, the current investigation concentrated on the effect of chloride-based salt (with a concentration of 5000 ppm to mimic the low salinity condition) at different pH values of 3.5, 7, and 11 in contact with heavy acidic crude oil (HACO). Since resin and asphaltene have a surfactant nature, resinous synthetic oil (8 % wt/wt) (RSO) and asphaltenic synthetic oil (8 % wt/wt) (ASO) were prepared by dissolving isolated resin and asphaltene using IP/140 procedure and examined. The results show that IFT can reduce to a value of 0.4 and 2.5 mN.m-1 for pH of 11 and DW solution if RSO and HACO utilize. The results also reveal that among the examined salts, NaCl and KCl introduce the highest impact for all types of model oils at pH values of 11, while no significant effect for pH values of 3.5 and 7 was obtained. According to these findings, it seems that injecting alkaline chemicals such as NaOH (which enhances aqueous solution pH) is an effective way to reduce the IFT values due to the in-situ surfactant generation and saponification of organic acids exited in model oils. Additionally, the IFT values show that although salts can retard the IFT reduction to some extent, no significant negative influence on the IFT reduction trends exist for the case of NaCl and KCl. •Increasing pH from 3.5 to 11 significantly reduces the IFT values for Heavy acidic crude oil.•Increasing pH from 3.5 to 11 significantly reduce the IFT value especially for resinous synthetic oil.•Chloride salts except CaCl2 introduce positive effects on IFT for pH values of 3.5 and 7.•Chloride salts introduce negative effects on the IFT for pH value of 11.•Increasing pH can generate in-situ surfactants by saponification.