When drilling infill wells in heavy oil oilfields of Bohai Bay after over teen years production, there are three challenges to achieve ideal production rate. The first one is wellbore stability in unconsolidated sandstone formation. The second one is risks of pollution and damage in pay zone with high porosity and high permeability. The third one is risks of mud loss and pollution in lower pressure pay zone after producing many years. CNOOC developed a reasonable technique according to the characteristics of pay zones, experiences of production and drilling. After successful applications, CNOOC formulated a good technique series which consists of membrane forming mud, completion fluid and flow-back in time. Production rate of the fifteen wells drilled achieved or exceeded the production allocation. This achievement is successful experiences to improve oil recovery rate and raise recoverable reserves and production rates.

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