As a new type of surfactant for oil displacement, internal olefin sulfonates have attracted much attention in oil field in recent years. As tertiary oil recovery technology is applied to high?temperature and high?salt reservoirs, the problem of temperature resistance and salt resistance of surfactant emerges. The rotating drop method was adopted to investigate the effects of ionic strength of Na? and Ca2? on the oil?water interfacial tension reduction performance of two internal olefin sulfonates (A?18, I?20) with different degrees of branching. The experimental results show that the internal olefin sulfonates surfactants generally have good salt resistance. Hydrophobic alkyl branching can increase the interfacial activity of surfactants. The active fractions in crude oil can be mixed and adsorbed with surfactant molecules at the interface, which is an important factor governing the interfacial performance. The increase of ionic strength can weaken the electrostatic repulsion among surfactant molecules and increase the adsorption capacity of surfactants at the interface. Moreover, divalent calcium ions exhibit stronger molecular aggregation ability than monovalent sodium ions, further reducing the oil?water interfacial tension at high mass fraction.

The study of the micro high viscosity mechanism of heavy oil is of great significance for the efficient development of Bohai heavy oil. Therefore, aiming at the typical heavy oil reservoirs in Bohai Sea, the microscopic mechanism of high viscosity of heavy oil is analyzed and studied from the aspects of viscosity?temperature relationship, crude oil composition and component polarity, heteroatom distribution and asphaltene aggregate structure. The results show that compared with N oilfield in Bohai Sea, the content of alkanes and aromatics in L oilfield in Bohai Sea is lower, and the quality score of resins and asphaltenes is higher, reaching 29.95% and 9.76% (23.25% and 6.59% in N oilfield). The quality score of heteroatoms such as O,N and S are high, and the relative molecular mass of resins and asphaltenes are also high. The polarity of each component is strong, and the dipole moments of resins and asphaltenes reach 14.01 D and 17.94 D, respectively (9.12 D and 12.25 D in N oilfield ). These will lead to stronger intermolecular forces and stronger intermolecular association between resins and asphaltenes. The smaller asphaltene molecular spacing and the denser aggregate structure,which will eventually lead to higher viscosity of crude oil.