Abstract: The oil wells of 2D wellblock in JX1-1 oilfield in Bohai sea are continually blocked by organic precipitation since been put into production. In order to improve the production condition of oil well, the wellbore treatment measure is studied. Firstly the oil components and physical properties are analyzed. Then the rheological property, components and element contents of organic precipitation are studied. The result shows that oil of 2D wellblock is general heavy oil with medium paraffin content. Its wax precipitation point is high and it has both wax and asphaltene precipitation risk. The major components of organic precipitation are asphaltene and other oleaginous constituents. Besides, the rheological property of organic precipitation will be worse after being heated with high temperature and re-cooled. Taking example by doping rare oil production technology of onshore oilfield, thin oil of adjacent wells is used to dissolve and disperse organic precipitation of 2D wellblock. The oil of B8 well is led into annulus of B25 well through Christmas tree to backwashing. After using thin oil backwashing to prevent organic precipitation blocking, oil production of B25 well improves 27.5% and the period of validity has been more than one year. Field practice indicates that thin oil backwashing wellbore can prevent organic precipitation blocking such as asphaltene and paraffin and so on. It has promotional value for similar oil field and wellblock.