This method uses a nitrogen booster to inject pressurized nitrogen into the annular space of the oil well to occupy the space in the wellbore with the nitrogen volume and its expanded volume after decompression. By displacing the flfluid in the well to create a negative pressure in the wellbore, making the pressure in the wellbore near the leak point lower than the formation pressure, and the formation flfluid flflowing into the wellbore through the leak point, Finally, use a visual detector to observe the flflow direction, flfluid state and tube wall conditions of the well flfluid in the wellbore in real time. Quickly and accurately locate to position the location of water outlet point of casing damaged wells. The fifield test results showed that this method can quickly and effectively locate the water outlet point of casing damaged, the test results are intuitive, reliable, and with high location precision. 

Keywords: Nitrogen gas lift ，Visual logging ， Water entry detecting

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