Normal production of 24 oil wells had been interrupted in fractured-vuggy carbonate reservoirs in Tahe oilfield due to blockage of wellbores by bitumen.Lab experiments of bitumen precipitation in mixture of condensate oil and heavy oil show that bitumen stemming is mainly caused by blending of condensate oil and heavy oil.This conclusion with the play characteristics in Tahe oilfield leads to the discovery that blocked wells are all located in the transitional zone from condensate oil to heavy oil.Based on the analysis of production performance

the article sums up the changing pattern of production performance before and after bitumen precipitation and proposes comprehensive prevention methods including blockage removing with addition of modified heavy oil as the core and prevention of bitument precipitation through injecting active water or formation water through annular space.The application of the methods had successfully cured 6 wells and resumed normal production.