A survey technique used to determine points of water entry in a producing well. One such survey involves three different types of operations. Under dynamic well conditions, the three surveys are run as follows:
(1) Temperature log. A continuous temperature profile is recorded over the interval of interest.
(2) Radioactive-tracer log: Ejected slugs of radioactive tracer material are monitored in order to determine the flow rate and direction.
(3) A conditioning survey is performed. To run a conditioning survey, a tool with a gamma-ray detector and an isotope ejector is run into the borehole. The isotope ejector is turned on, and the tool is lowered through the production interval at constant speed. A gamma-ray log is run during the “conditioning” run in order to provide a base log to which subsequent gamma-ray logs can be compared. Several subsequent gamma-ray logging runs are then made through the conditioned interval. Water from the formation entering theborehole will produce dilution of the isotope-treated fluid in the borehole, and an upward displacement of the treated water column will occur. The combination of surveys is then interpreted.