Naturally Occurring Radioactive Material Logging

Abstract

ABSTRACT The phenomenon of scaling in both downhole and surface production equipment is well knownwhere water-drive reservoirs are in production. Sulfate scales, consisting mainly of barium,strontium, and calcium, occur on surface and downhole equipment. Traces of radium may be present in such scales, making them radioactive. Removal and cleaning of such scaled equipment for later use can present a potential health hazard. Alternatively, the equipment may have to be removed, stored, and disposed of according to established procedures for low-level radioactive waste. Measurement of radiation levels at the wellsite requires the use of rugged gamma ray survey meters by specially trained personnel. Measurement of low levels of radiation on individual tubing sections can be difficult in the presence of natural background radiation. However,gamma ray well logging tools are very sensitive instruments and can make radiation measurements inside scaled tubing in the well with less sensitivity to background signal. To evaluate scale radioactivity before removing the tubing from the well, a reconnaissance logging technique has been developed that uses a gamma ray logging tool calibrated specifically for radium. This new technique allows better decisions to be made prior to removing the tubing. In this paper, procedures used to calibrate the logging tool are described, together withmeasurements made to correct for the effect of tubing wall thickness. Field examples are presented where this technique has been successfully applied.