Abstract: To further explore the displacement mechanism of flexibility of the polymer to the residual oil， upper-
convected Maxwell constitutive equation is selected， and flow equations of the viscoelastic fluidflow in porous
road are established. The horizontal deviatoric stress difference on the residual film iscalculated on the basis of the
stress tensor theory. The impacts of the different rheological fluid， thewidth of oil film， and pressure gradient on
the horizontal deviatoric stress difference on the residualfilm are analyzed and compared. The results show that：
When flooding with water， power law fluid（n = 0.6） and viscoelastic fluid（We= 0.3） ， the ratio of horizontalde-
viatoric stress difference on the residual filmis about 1：10：25 at actual oil production mean pressure gradient of
0.02 MPa/m， which means that the driving force of viscoelastic fluid（We = 0.3）on the film is about 25 times
the water flooding. This innovative conclusion that the microscopic displacement efficiency can be improved by
viscoelastic fluids is further proved theoretically.

Key words: viscoelastic fluid, residual Oil, micro force, displacement efficiency, flexibility