The annular foam breaker is one which uses the vacuum and shear force generated by the Coanda effect to break foam. Its effectiveness in destroying drilling foam has been tested in wellbore flow simulation loop experimental stand. Experimental results showed that the operating pressure of the annular foam breaker should be larger than 0.6MPa and the stabilizers concentration of the foam drilling fluid should be as low as possible so as to obtain higher foam-breaking efficiency. Moreover, the

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... ular foam breaker was more effective to destroy wet foam system. When the gas to liquid ratio of the foam was lower than 100, the foam-breaking efficiency was up to 85%. From the results obtained in Yuanba-10 well located in Sichuan province of China, it can be drawn that the annular foam breaker had a high efficiency that only 400 m 3 foaming solutions was consumed with total 672m of foam drilling footage in 26 in. section. The consumption of ingredient additives and water were decreased drastically with using the annular foam breaker, which reduced the foam drilling cost sharply.