Research On Viscosity Characteristics And Adaptability Of Low Molecular Weight PAM Used For EOR

The tertiary-main layers reserves is very high in China, but the injection of oil displacement agent and oil recovery are very difficult, thus the low molecular weight polymer flooding was used to exploit tertiary-main layers. However, the viscosity was unstable and the high viscosity loss rate seriously affected the recovery of tertiary-main layers in field application. According to this situation, the low molecular weight polymer used in test oil field was taken as research object, its viscosity characteristics and the adaptability to tertiary-main layers were studied in this paper.The method of simulation test combined with field monitoring was used in this paper. Firstly, the physical and chemical properties, molecular weight distribution and viscosity stability of low molecular weight polymer were researched. Then, aiming at the problem of high viscosity loss rate in field application, the concentration, temperature, suspended solids, salt and mechanical shear were studied through laboratory simulation test. At the test of mechanical shear, the effect of friction shear and perforation shear or porous media shear on viscosity were studied by self-made device, besides the rotating shear. Furthermore, the oil-displacement capacity of polymer after mechanical shear were also studied. Finally, the adaptability to tertiary-main layers of low molecular weight polymer was studied according to the application situation of test area.Research shows that there is some correlation between molecular weight distribution and viscosity stability of low molecular weight polymer, the more narrow the peak-type of molecular weight distribution, the higher the viscosity stability. The perforation shear or porous media shear, rotate shear, and salt has great influence on the viscosity of polymer solution. The polyacrylamide viscosity loss rate was up to 57.2% to the concentration of MB 1100mg/L and mol.wt 800×10~4 under the condition of shear surface diameter 38μm, pressure 1.2MPa and perforation four times. When rotary shear rate was 1.0×10~4rpm and shear time was 40min, the viscosity loss rate could reach 66.1%. The viscosity loss rate was 76.3% under the condition of salt concentration 6000mg/L. The results of adaptability of low molecular weight polymer show that the 800×10~4 mol.wt polyacrylamide is better than 400×10~4 for polymer flooding.These results provide a theoretical basis for the application to tertiary-main layers of low molecular weight polymers, and has important reference value for recognizing the problems existing in the polymer flooding and enhancing the oil recovery.