Method and apparatus for detecting and quantifying radioactive material

Abstract

In order to properly treat the tubing of an oil producing borehole, and prevent hazard to personnel at the oil production site, the contamination of tubing by the formation of scale or radioactive deposits on the inner wall thereof is determined by measurement of the low-level radiation emitted by the scale and calculation of the radiation level which would be detected in the vicinity of the outer wall of the tubing in the absence of contributions by the radioactivity of surrounding earth formations. This is accomplished by a logging tool and method which includes a sonde which includes a detector and is lowered in the tubing to detect and count the gamma rays emitted by the scale or radioactive deposits at different depths in the borehole tubing. Data processing determines the radioactivity level within the tubing from the measured gamma rays, and calculates from that level the level of radioactivity which would have been detected outside and in the vicinity of the tubing by applying a first tubing thickness attenuation factor. In a preferred embodiment, data processing corrects for the natural background radioactivity level by subtracting a reference natural radio activity level, itself corrected for tubing thickness by applying a second tubing thickness attenuation factor.