Radioactive Tracers in Geophysics

Radioactive tracers are widely used.in geophysics for solving various problems of the oil industry. The main applications are the following: (a) In injection wells, determining water formations and checking conditions in casings; (b) In producing wells, determining annular circulation and checking casing conditions; (c) Determining the level of the cement top when deep wells arc encased in concrete, especially in regions of elevated temperature. To solve these problems use is made of the isotopes 59Fe, 95Zr, 65Zn,and 13I. In doses ranging from 0.5 to 1 mCi per m3 of solution. The following will give some idea of the scope of the investigations being carried on with radioactive tracers: At the Romashkinsky deposit in the Tatar Autonomous SSR, a total of 220 wells was investigated in 1965 with a view to resolving the problems listed above. Of these, 150 were injection wells and 70 producer wells. In-the oil deposits of Western Turkmenistan, 132 wells were investigated with radioactive tracers in 1965. In recent years there has been a considerable reduction in the.work involved in detecting zones of hydraulic fracturing, determining cement ring thickness in the cementing of wells and delimiting the oil- bearing beds and water formations in a layer. This is due to the successful solution of these problems by other methods (radial cement thickness indicators, INM etc.) and the achievement of safe methods of work. Of late, increasing use is being made of tritium as a tracer, e.g. in determining the rate-of. water movement in a layer during the working of deposits, in techniques for pressure maintenance of fields, and in solving problems relating to the hydrodynamic relationships between individual layers and productive zones in massive oil fields. These problems are being solved by methods based on the use of radioactive tracers In aqueous form. Natural tritium is beginning to be used in solving problems relating to the extent of surface water infiltration and flooding in mine workings. The paper discusses the technological questions arising in the use of these methods, the problems which have been solved and the economic advantages. (author)