| The rate of penetration could obviously decrease with the increase of well depth during deep and ultra-deep well drilling operations. One of the significant reasons is that the rock debris there can't be removed timely due to bottom hole differential pressure, which lead to repeating breaking of rock performed by drill bit. On the basis of the theory of bottom hole negative pressure fluctuation increasing rate of penetration, the chip hold effect could drop through the fluctuation split-flow drill bit, and rise could the rate of penetration. Fluctuation split-flow drill bit connected to bistable fluidic element was developed according to venture effect and water hammering, which succeed earlier stage research project. It is proved in numerical simulation and indoor experiment that, there is 27% to 62.5% improvement on depressurization effect when pressure fluctuation in bottom hole compared with previous research, and it possesses sharp advantage in contrast with preceding negative pressure fluctuation instrument. Under certain conditions like pump delivery 40L/s, drill bit pressure drop 10MPa, bottom hole hydrostatic column 30MPa, drill fluid switchover frequency 50 Hz, the negative pressure amplitude could reach up to 10MPa and beyond. Diverse factors including structural parameters and hydraulics that affect the bottom hole flow field pressure fluctuation were analyzed taking advantage of numerical simulation and indoor experiments. It is observed that, the distance between the export section of suction nozzles and bottom hole surface, the ratio of equivalent diameter of nozzle combinations affect the flow field pressure fluctuation great, while switchover frequency, distribution time of drill fluid through nozzles, hydrostatic column in bottom hole have limited influence on it. In addition, magnify the pump delivery could enhance pressure fluctuation effect when constant structural parameters.
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