Water injection profile variation of oil layers under polymer flooding

Statistical analysis in Daqing Oilfield indicates that the water injection profiles of low-permeability reservoirs retrograde when the injected polymer volume amounts to 0.08-0.2PV in most wells,and the retrograde time is earlier than that of mid-permeability reservoirs,and high-permeability reservoirs remain highest injectivity during the whole polymer flooding,which is unfavorable for improving the development results.Simulation shows that the bigger the reservoir permeability contrast and the effective thickness ratio of reservoirs,and the smaller the molecular weight of injected polymers,the poorer the adjustment results of polymer solution to the water absorbing capacity of low-permeability reservoirs;the reservoir productivity factor contrast is the main factor affecting the retrograde time and retrograde period of the water injection profile.The following measures are proposed to improve the results of polymer flooding: avoiding big reservoir productivity factor contrast in the combination of strata;separate polymer injection;optimizing the molecular weight of injected polymers and the combination of injected polymer slugs;and depth profile control before injecting polymers etc.