Analysis on leakage pressure of buried-hill granite gneiss in BZ19-6 structure

Circulation loss of different degrees occurs during the drilling of the buried hill strata in BZ19-6 structure.The key to prevent and plug lost circulation is to confirm the leakage pressure reasonably.In this paper, the leakage mechanisms of fractured formations were analyzed.Then, from the viewpoint of statistics, the correlation between the leakage pressure difference and the leakage rate was put forward.Finally, a leakage pressure model for fractured formations of buried hills was established and verified based on the actual leakage point of BZ19-6 structure.It is shown that the depth of leakage points in BZ19-6 structure is mostly in the range of 4 200-5 300 m, and the lithology where the leakage occurs is granitic gneiss.The leakage in buried-hill formations is mainly micro-minor fractured leakage.It is the power function relationship between the leakage pressure difference and the leakage rate.The calculated bottom hole pressure is higher than the leakage pressure at the actual leakage points of BZ19-6 structure, which conforms to the engineering practice.In conclusion, the fractured leakage model established in this paper can provide the guidance for the future design of drilling fluid density.