Petroleum sulfonates are widely used in chemical flooding in China. The samples are complicated and not all the fractions are effective. To recognize effective fraction with excellent interfacial activity and emulsifying property, a preparative liquid chromatography technology was adopted to perform the fraction separation for petroleum sulfonate. Structural composition, interfacial activity，emulsifying property and flooding efficiency of obtained fractions were also analyzed and discussed. It was shown that petroleum sulfonate can be effectively separated into different fractions with obvious structural differences, among which one fraction with the most excellent interfacial activity and the emulsifying property was recognized. The average molecular weight and molecular weight distribution range of this active fraction were 455.5 and 428–468, respectively, which are both crucial for activities. Alkylbenzene dicyclohexane sulfonates, alkyl indan sulfonates, and alkyl naphthalene sulfonates are major structure types, and alkyl chain length is mainly distributed between 12–15, 15–17 and 15–17 respectively. Besides, this active fraction is universal, and it can produce ultralow interfacial tension (~10−3 mN/m) and good emulsifying property against different crude oils including Xinjiang, Changqing, Liaohe Oilfields, etc. in China. The developed technology herein can be used to track and confirm the characteristics and/or active fraction in petroleum sulfonate accurately.
Petroleum is one of the most important resources, and meanwhile, it is one of the scarcest resources in China. It is crucial to exploit underground petroleum as much as possible. However still approximate twothirds of crude oils remain in the reservoir after the primary (pressure flooding) and secondary (water flooding) production (Resen et al., 2005; Wang et al., 2014). As a result, many enhanced oil recovery (EOR) techniques have been developed, especially surfactant flooding (Liu et al., 2007; Khan et al., 2009; Dong et al., 2008; Elraies et al., 2011; Hirasaki et al., 2011; Shahri et al., 2012; Ma et al., 2017; Feng et al., 2018). The key to surfactant flooding is to search suitable surfactants, which can reduce interfacial tension (IFT) to an ultra-low level (<10 2 mN/m, even <10 3 mN/m), and/or enhance emulsifying property between the crude oil and the surfactant solution (Santanna et al., 2009; Zhang et al., 2010; Wang and Dong, 2010; Nguyen et al., 2012; Xie et al., 2012; Zhou et al., 2013; Jeirani et al., 2014; Shang et al., 2015). Among the surfactant flooding, petroleum sulfonate is most widely used in China owing to its good interfacial activity, wettability, foam properties, and salinity tolerance, etc. (Sun et al., 2015).