Abstract: The membrane structure characteristics, efficacy and mechanism of a membrane filtrate reducer CMJ-2-XNJ-1 have been introduced. And the properties of the water based drilling fluid composed by CMJ-2-XNJ-1 with cover additive JH-1,viscosity reducer JN-1 have been studied. Results indicate that CMJ-2-XNJ-1 can form membrane structure with excellent performance, and its water based drilling fluid system has excellent flow property, low filter loss and thin cake, strong inhibition, good lubrication, good salt resisting, strong temperature resisting, and anti-contamination and good protection of oil reservoir. The system has no fluorescence and toxicity, it can meet the needs of environmental protection.

Key words: membrane filtrate reducer, membrane structure, water based drilling fluid, performance of steady wall, protection of oil reservoir, environmental protection