Recent Developments in the Use of Radioactive Tracers in the Romanian Oil Industry

Recent work with tracers has been concerned with the use of stable tracers having special nuclear properties which enable them to be detected under industrial conditions, and also with the simultaneous use of several tracers. The first part of the paper deals with the industrial-scale use of cadmium as a tracer in oil pipelines. To eliminate the handling of open radioactive sources, the authors have developed a labelling method involving the use of a non radioactive substance containing an isotope with a large cross-section for thermal neutron reactions, which they irradiate with a neutron source. For this purpose they use natural cadmium, in the form of CdSO4. The experiments were performed in the laboratory, on sections of industrial-type pipe, in different geometries and with different concentrations of CdSO4. The authors measured the counting rates for thermal neutrons with a BF3 counter and for capture gamma rays with a scintillation counter; they also determined the sensitivity threshold. The results are presented in the form of graphs and discussed. Using cadmium naphthenate, they also carried out experiments in situ. The second part of the paper is devoted to a multiple tracer study of the procedure for water injection in oil wells. The authors first set out the principle of their method, which consists of injecting water into injection wells so as to promote secondary recovery of oil and improve oil yield. They describe in detail how they monitor water movement through the layers of the injection wells (located at the corners of a zone in the shape of a square) to the reaction well by the simultaneous use of 131I, 65Zn and D2O (which they were able to detect selectively) and with the help of filtration devices for retaining the radionuclides. The results obtained show that the water has a tendency to become channelled. These results are in-agreement with the water mineralization measurements in the reaction wells. The procedure described can also be extended to other branches of industry. (author)