Abstract: Full range heavy alkyl benzene sulfonates were cut into a series of narrow fractions of HABS and then sulfonated. According to their molecular weight, the sulfonated narrow fractions are called HABS-1, 3, 5, 7, 9. The crude oil from Xinjiang 530 oilfield reservoir was used as oil phase, and its formation water in this oilfield as water phase. The effect of full range HABS and narrow fractions on emulsifying stability and interfacial tension (IFT) were measured, respectively. The results showed that the IFT value goes down firstly and then up with the increase of its molecular weight. The HABS with average alkyl carbon chain length of C15 (molecular weight of 398) can reduce the IFT level to 0.002 3 mN/m. The results of stability of oil-in-water emulsion showed that when HABS-3 mixed with HABS-1 (HABS-3:HABS-1=85:15) or with nonionic primary alcohol ethoxylate AEO-9 (HABS-3:AEO-9=85:15), the systems attain strong emulsion stability with emulsion composite index of 89.51% and 88.70%, while the IFT value is 0.009 8 mN/m and 0.005 9 mN/m, respectively, both are at 10-3 mN/m (ultra low) level.

Key words: heavy alkyl benzene sulfonate, composite system, emulsion property, interfacial tension