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|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 detectors|gamma-ray detector]] and an [[isotopes|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|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.