Abstract: An apparatus and method are provided for varying an operating parameter for a nuclear gamma ray tool for evaluating the integrity of gravel packing. The gamma ray outpat intensity and area of investigation are altered by changing a source housing geometry and the material from which the source housing is made. An actuator is provided to slide a variable electron density sleeve over the source and to vary the area of investigation by changing the distance between the source and a detector.

Abstract: The present invention provides apparatus and method for evaluating the integrity of gravel packing. A screen is disposed in an annulus between the wellbore and a production tubing. A tubing, such as a wash pipe, is placed inside the production tubing to provide a fluid path for the gravel slurry for gravel packing the screen. A self-contained memory logging nuclear tool is located in the tubing below (downhole) the screen. After gravel packing, the tubing with the tool is retrieved from the well at a selected speed. The tool is activated to record data in the memory carried by the tool as it passes across the screen. The data stored in the memory is downloaded at the surface to produce a log which provides a measure of the integrity of gravel packing of the screen.