In the laboratory study of the phase behavior in microemulsion system formed by mixing various equivalent weight petroleum sulfonates and iso-alchols (isobutyl alcohol, isopentyl alcohol) with Daqing Desassed crude oil, an abnormal phase behavior has been observed. Various formulations of the petroleum sulfonates give little solubilization of the crude, so that it is very difficult to evaluate the best equiepments eight of petroleum sulfonate by use of its solubilization parameters. In this study, procedures, which can form the best middle phase and are related to the phase change, are selected to study the method of increasing the solubilization of abnormal phase behavior crude oil and decreasing the interfacial tension under the reservoir temperature and salinity in Daqing reservoir. Tests show that increasing the av. equivalent weight of the petroleum sulfonates, increasing the carbon chain length of the alcohol and using the mixed alcohols, can improve the solubilization of the crude oil, decrease the interfacial tension, and give a wider range of the salinity for optimization of the displacement-of-oil system.

In the formulation of microemulsion with Daqing degassed oil, a linear relationship between the av. equivalent weight of the petroleum sulfonate and the log of the optimum salinity was obtained. It can be seen from this curve that the optimum av. eq. wt. of the petroleum sulfonate is 522+. Based on this paremeter, TRS-18, PHH and P-HMW with av. eq. weight of 500+ are selected to give a better displacement-of-oil system with a interfacial tension as low as 10-3 m Nm-1.

Results of the tests demonstrate that the method for obtaining an optimum formulation of a microemulsion system proposed by Solager et al. can not be used in case of Daqing abnormal phase behavior crude oil.

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