The isotopes uranium-238 and thorium-232, and the radioactive isotopes associated with the decay series of these isotopes, occur in nature in earth formations. In situ, the activities associated with these decay chains are relatively low and do not present a radiation hazard during the drilling operation. During well production, however, these naturally occurring radioactive materials (NORM) are dissolved in the produced waters and are transported to the surface. Over an extended period of time, the NORM becomes concentrated in precipitated scale associated with tubulars and surface equipment such as heater treaters, wellheads, separators and salt water tanks. Although the parent isotopes uranium-238 and thorium-232 are not generally present, the decay products or daughter products radium-226, radium-228, radon-222 and lead-210 can be found in oilfield waste. Radium-226, which coprecipitates with carbonates and sulfates of calcium, barium and strontium, is by far the greatest source of radioactive waste resulting from production activities. Once atoms of radium have replaced a sufficient number of atoms of the elements normally found in NOW waste to exceed a specified regulatory level, the waste is classified as NORM. Stated another way, there is no difference between NOW and NORM waste other than the level of radioactivity, which usually results from the radium content of NORM waste.
Posted on: Fri, 26 Sep 2014 02:58:36 +0000
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