Abstract: In drilling operation process,overflow and well leakages need to be monitored in a timely manner and established so that the appropriate well control measures can be taken.In order to achieve the target of"1 m3 discovery and 2 m3 shutdown",the innovative development of an existing overflow monitoring system was carried out.The elevated slot of drilling fluid was changed to double baffle structure.The first baffle plate was used to alleviate the fluctuation of the liquid level by reducing the flow velocity of drilling fluid and the second baffle plate was used for the accurate measurement of liquid height deviation by adjusting liquid level height.The design of floating ball device of the drilling fluid tank by using the principle of U tube had effectively eliminated the fluctuation of the liquid level outside the filter cylinder.Meanwhile,the floating ball solved the problem of bubble accumulation and could accurately measure the volume change in of the mud pit after the occurrence of well leakage or overflow.This device was widely used in more than 60 wells and the overflow only occurred in 6 wells in total.Overflow detection accuracy was 100%.After the well was shut in,the overflow amount was less than 2 m3.The device could detect the overflow more promptly and accurately than the traditional methods of using human beings to record the data.The field application showed that this device could effectively enhance the ability to attain sensitive measurements of overflow and well leakage,solve the problem of overflow detection delay in the field and provide technical support for the accurate detection of overflow.