Producing Patterns and Improvement of Polymer Flooding Profile in Class ⅡB Reservoir,Daqing Oilfield
The application of polymer flooding is expanding in Daqing oilfield,with the target transferring to poor-quality Class ⅡB reser-voir.The existing polymers exhibit poor compatibility with the reservoir,the producing patterns of the profile remain unclear,and the ef-fects of polymer flooding development vary greatly in different areas.To address these issues,through the analysis of field profile data sta-tistics and laboratory experiments,the producing patterns and improvement methods for the profiles in Class ⅡB reservoir were investigat-ed.In view of the producing status from water-injected layers,Lamadian area which is characterized by thick channel sandbodies and good reservoir properties exhibits the highest proportion of net pay producing,with the reservoir exploited frequently,multiple polymer break-through layers,and relatively high liquid absorption.The Sazhong and Sanan areas,with limited channel sandbodies and multiple thin sand layers with poor properties,show a low net pay producing proportion in the water flooding stage,after polymer flooding which is 12.5%and 15.4%higher than those in the water flooding stage,respectively.Additionally,the reservoirs with permeability ranging from 100 to 300 mD show a significant profile improvement.In view of the producing status of water-unswept layers,the strong vertical heterogeneity of Class ⅡB reservoir results in a high net pay unproducing proportion between layers.In this case,the profile should be improved by achiev-ing balanced interlayer production.The alternating injection of salt-resistant polymer of high and low concentrations can delay the rise of water cut,enhance the liquid absorption in low-permeability layers,and significantly improve the recovery efficiency of polymer flooding.A pilot test on alternating injection of DS1200 salt-resistant polymer of high and low concentrations was conducted in A area of Beibei block in Lamadian,achieving satisfactory water-cut reduction and oil increment.This technology provides a guidance for improving the polymer flooding profiles of Class ⅡB reservoir in Daqing oilfield.
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