The rheological behavior of HPAM solutions and Xanthan solutions

their rheological behavior in porous media and residual resistance factors were measured experimentally

and the depleted layer thickness was calculated．Displacement experiments were proceeded with various concentrations and injecting speeds．It was expounded that the increase of apparent viscosity or the decrease of depleted layer thickness generated by the entanglement of polymer molecules can increase the force parallel to oil-water interface

which can pull more residual oil out and enhance oil recovery．With the concentration increase of HPAM solutions

the apparent viscosities increase and the depleted layer thickness decrease．When the concentration of Xanthan solutions was higher than the entanglement concentration

the depleted layer thickness and the apparent viscosities varied little．The increase of injecting speed can decrease the depleted layer thickness of both polymers

with residual resistance factors varying little and viscoelasticity increasing for HPAM solutions and residual resistance factors decreasing for Xanthan solutions．The flooding results with various concentrations and injecting speeds affirm the mechanism that the entanglement effect and the depleted layer effect of polymer molecules act on the residual oil．The difference in molecular structure of the two polymers used is the essential reason that results in their different flow behavior in porous media and different mechanism of action on residual oils.