Abstract: In view of spalling off,sticking and other complicated problems which occurred when drilling a long horizontal section in tight oil reservoir of the Daqing Oilfield,we conducted optimization operations for the properties of the previously used high performance water-based drilling fluid.We also adopted an auto-synthesis effective polyamine inhibitor,combined with the multiple inhibition effects of polymeric alcohols and inorganic salts to enhance the inhibition performance of the drilling fluid system.The "cloud point" effect of polymeric alcohols and the double plugging effect of nanometer emulsion plugging agents were used to improve the plugging ability of the system.The synthetic environmental-friendly liquid lubricant and solid emulsifier were used to improve the lubricity of the system.After optimization of the high-performance water-based drilling fluid,the shale rolling recovery rate was higher than 95%.Further,the micro-crack plugging width was no more than 100 μm,and extreme pressure lubrication coefficient was lower than 0.12.This new,optimized high-performance water-based drilling fluid was applied in over 50 horizontal wells in tight oil reservoir of the Daqing Oilfield.As demonstrated by the application results,the average expansion rate of hole diameter was lower than 10%,the drilling cycle was shortened by more than 3.0 d,and the longest horizontal section was 2 033.50 m.The study results demonstrated that the optimized high-performance water-based drilling fluid could meet the drilling requirements of the Daqing tight oil reservoir.Further,the results could provide a technical foundation for the efficient development of unconventional tight oil reservoir.