Interfacial Tensions between Petroleum Carboxylates of Different Carbon Chain Length and Different Normal Alkanes

The IFT (stabilized value of dynamic interfacial tension) between petroleum carbxylates (PCs) A,B, and C prepared by oxidation and sponification of fractions of Daqing crude with average carbon number 23.16, 26.01, and 28.70, respectively, and normal alkanes nC7, nC12, and nC16 determined at 45℃ is investigated in relation to NaCl mass concentration of aqueous phase,1 g/L aqueous solution of PC. For every alkane under study, the salt requirement (SR) range to create ultralow IFTs is narrowed and the SR value corresponding to the lowest IFT reached, or the optimal SR value, is lowered with increasing the average carbon number of the PC used; for every PC under study, the SR range to create ultralow IFTs is widened and the optimal SR value is rasised but the difference from each other is diminished with increasing carbon number of the alkane taken. The proper choice of PC species appears to be A, B, and C for nC7, nC12, and nC16, respectively, according to the IFT values reached and the SR range and the SR optimal value needed. The results obtained indicate that there exist some correlations between average carbon number of PC and carbon number of alkane and between carbon number of alkane and SR in ultralow IFT systems; both EACN of the crude and sanility of the reservoir brine should be considered for a given PC to be put into use.