Radionuclide concentrations in oil extraction and production processes in Northeast Brazil

Since the beginning of the twentieth century the presence of naturally occurring radioactive material (NORM) was detected in the water and oil extracted from wells both onshore and offshore. The oil is extracted together with water and sediments which contain radionuclides of the uranium and thorium series. Among the radionuclides present, especial attention should be given to 226Ra and 228Ra, due to its long half-life and importance, from the radiological point of view. The objective of this work was to identify the natural radionuclides in the oil industry, to determine their activity concentration, and from these results, to evaluate the risks the employees of the oil industry are exposed to. Samples of sludge, scale and produced water extracted with the oil were collected from three oil processing stations in the state of Sergipe, Brazil. The activity concentrations of the radionuclides were determined in the solid samples before and after the extraction of the oil. The chemical and mineralogical composition of the samples without oil was evaluated. Water samples, on the other hand, were analyzed for their contents of radionuclides and barium concentration. It was observed that the activity concentrations of the analyzed radionuclides (226Ra, 228Ra, 228Th and 210Pb) in sludge and scales were very high when compared with the literature, particularly much higher than the values for 226Ra and 228Ra obtained for sludge and scales from the oil platforms near the city of Campos, state of Rio de Janeiro. The maximum concentration values for 226Ra, 228Ra, 228Th and 210Pb (3,500, 2,195, 2,248.6 and 201 kBq kg-1, respectively) were obtained for the scales after the extraction of the oil. The analysis of the samples showed that barium sulphate (barite) and strontium sulphate (celestite) are the main constituents of the scales, while carbonates and silicates, together with other compounds are the components of sludge. A correlation between barium, 226Ra and 228Ra was observed for the produced water, confirming that these radionuclides are brought to the surface together with the barite. The levels of radioactivity found in the oil collecting stations investigated indicate that special care must be taken in order to protect the employees and for the correct management of the radioactive residues. (author)