. USE of RADIOACTIVE IODINE as a TRACER In WATER-FLOODING OPERATIONS Downloaded from http://onepetro.org/jpt/article-pdf/6/09/117/2237549/spe-349-g.pdf by guest on 27 September 2021 J. WADE WATKINS BUREAU OF MINES MEMBER AIME BARTLESVILLE, OKLA. E. S. MARDOCK WELL SURVEYS, INC. MEMBER AIME TULSA, OKLA. T. P. 3894 ABSTRACT assumed that the physical conditions in the productive formation are homogeneous. Unfortunately, homogen­ The accurate evaluation of reservoir-performance eous conditions rarely, if ever, exist in oil-productive characteristics in the secondary recovery of petroleum formations. The use of a tracer that may be injected by water flooding requires use of a water tracer that into an oil sand and detected quantitatively, or even may be injected into water-input wells and detected at qualitatively, at offsetting oil-production wells provides oil-production wells to supplement data obtained fronz basic data that may be used in determining more core analyses, wellhead tests, and subsurface measure­ accurately the subsurface rates and patterns of flow ments. Radioactive iodine has been used successfully of injected water between wells than is possible by as a water tracer in field tests to determine: (1) rela­ theoretical calculations based on assumed conditions. tive rates and patterns of flow of injected water between Consideration of the data obtained by using a water water-input and oil-production wells and (2) zones of tracer assists in the application of remedial measures excessive water entry into oil-production wells. to water-input wells, such as plugging of channels, or Laboratory evaluations of potential water tracers, selective plugging of highly permeable zones, thereby previous tracer studies, the value of using a radioactive effecting a more uniform flood and a greater ultimate tracer, general field procedures, and the use of surface oil recovery. and subsurface instruments for the detection of the emitted gamma radiation, are summarized. Data from A water tracer should have the following charac­ the field tests are presented graphically and discussed t~ristics: (1) low adsorption on solid reservoir mate­ in detail. rial; (2) high solubility in water; (3) low or negligible It is concluded that the radioactive-tracer method, solubility in crude petroleum; ( 4 ) a wide range of using radioactive iodine, may be used successfully to solubility of compounds that may be formed by chemi­ measure either the relative rates and patterns of flow cal reactions with ions present in reservoir rocks or waters; (5) high detectability in low concentrations by or zones of excessive water entry into wells under condi­ tions of comparatively rapid transit time between wells. portable apparatus; and (6) general availability at low cost. Additional desirable characteristics are that the tracer should be nonhazardous in nature under normal INTRODUCTION working conditions and quantitatively detectable in the Extensive use is made of data obtained from core well bore, as well as at the surface. analyses, wellhead tests, fluid characteristics, and sub­ surface measurements in evaluating the sweep efficiency REVIEW OF PREVIOUS TRACER STUDIES of water injected into oil sands for the recovery of oil. Theoretical flow rates and patterns may be calculated The need for a water tracer has been recognized for from those data using radial-flow formulas, if it is many years. As far back as 1906, Dole' described the use of fluorescein in flow-rate studies made in France 1 References given at end of paper. in 1901. In 1921, Ambrose' discussed in detail the use Manuscript received in Petroleum Branch office Jan. 11. 1954. of organic and inorganic dyes, chlorides, nitrates, and Paper presented at Annual AIME Meeting in New York City. Feb. 13-17. 1954. other anions, lithium salts, and the Slichter electrical PETROLEUM TRANSACTIONS, AIME SPE 349-0 117 method for tracing the underground flow of oil-field radioactive isotopes, and standard methods of quan­ waters. More recently, several articles on the use of titative analysis were used. water tracers in oil production have been published. It was believed that radioactive tracers would be Sturm and Johnson' presented the results of field tests superior to stable ones because: (l) they may be easily in Pennsylvania oil fields in which fluorescein, chlorides, detected in low concentrations; (2) they may be de­ and surface-active agents were employed as water tected by subsurface instruments if the emitted radiation tracers. Carpenter and others' discussed several field is gamma or hard beta; and (3) the necessary radiation­ tests in Mid-Continent oil fields in which boron, as detection equipment may be made portable. borax and boric acid, was used as a tracer. Quite recently, Garst and Wood' presented the results of Consequently, instruments were assembled, and the experimental field tests in which stable (not radioactive) necessary permission was obtained from the Atomic copper and iodide salts were used as flood-water tracers. Energy Commission to make field tests using radio­ In 1945, Plummer6 discussed the general subject of active iodine (iodine 131) as a water tracer. water tracers, including many of those previously men­ tioned, as well as radioactive tracers. GENERAL FIELD PROCEDURES Archibald' reported the results of surface flow tests All field radioactive-tracer tests described herein were made in 1949 in which radioactive iodine was used as made by the Bureau of Mines in cooperation with Well a tracer in field tests. In 1950, Coomber and Tiratsoo' Surveys, Inc., Tulsa. Under the existing cooperative published the results of laboratory flow tests in which agreement the Bureau of Mines has procured and radioactive iodine was used as a tracer in the oil phase injected the radioactive iodine used as the water tracer Downloaded from http://onepetro.org/jpt/article-pdf/6/09/117/2237549/spe-349-g.pdf by guest on 27 September 2021 in laboratory flow tests. Several patents have been issued and made all surface measurements of radioactivity. that bear on the injection of radioactive materials into Well Surveys, Inc., has made all subsurface gamma-ray water-input and oil-production wells for various pur­ and neutron logs and radioactivity input-profile logs on poses, such as those issued to French' in 1947, describ­ water-input wells. ing the use of a radioactive gas, and Hinson'° in 1951, describing the use of radioactive gases, liquids, and Before a location was selected for a field tracer test, solids for determining flow rates and patterns of fluids all available information concerning the wells and reser­ injected into subsurface strata. A patent also has been voir characteristics and performance was evaluated. issued to Bond and Savoy" bearing on the use of Injection rates and pressures on water-input wells were acetylene as a tracer gas in both gas and water-injection examined to determine anomalous conditions thereby operations. indicated, such as abnormally high injection rates or low injection pressures. Despite the attention evidenced in the subject by the above-cited references, nothing has been published con­ The first step in the field tests was to obtain a cerning the successful or attempted use of radioactive water-input profile on the well selected for tracer injec­ water tracers in field secondary-recovery operations. tion by the use of the Well Surveys, Inc., radioactivity input-profile method. If caliper measurements were not available on the holes used in the tracer tests, those LABORATORY EVALUATION OF TRACERS measurements were made (especially if the sand had been shot) as part of the profile measurement and to In July, 1947, a water-tracer study was started in the assist in the interpretation of radioactivity logs. Bartlesville laboratories of the Bureau of Mines, but the study was temporarily discontinued in January, Standard gamma-ray and neutron logs were made on 1948. Several tracer substances were considered during the input well as well as on all production wells at this period, and field tests were made using the ammon­ which the tracer might appear, using conventional ium ion as a tracer. The results, however, were unsatis­ gamma-ray and neutron ionization-chamber instruments. factory because of the high concentration of ammonium This equipment is the same as that used commercially ion in many produced waters. Laboratory tests were by the licensees of Well Surveys, Inc. These logs corre­ made with fluorides with inconclusive results. At the lated the lithology of the formation with core-analysis time the study was discontinued, the expressed opinion data and provided the necessary background informa­ of the chemist in charge of the work was that radio­ tion for the tracer surveys. active tracers appeared to offer the greatest promise. If the data available indicate that the water is passing A radiochemical laboratory was completed, and the rapidly from the input to the production wells, it may tracer study was resumed in 1951. Numerous selected be advisable to make a dye-tracer test before injecting substances were tested to determine their adsorption the radioactive tracer. The purpose of this test in the characteristics by passing "slugs" of the material in Bureau of Mines field work was to determine the water through long, consolidated sandstone cores, sealed approximate transit time from the water-input well to in plastic, and measuring quantitatively the tracer in the production wells. This information permitted sched­ the effluent fluid. Substances for tests were selected uling arrival of the gamma-ray logging crew at a time primarily on the basis of the solubility of their common that would permit locating the subsurface logging compounds and secondarily on the basis of expected instrument in the borehole of the production well at low adsorption characteristics. Fluorescent dyes were which the tracer first appeared without excessive wait­ among the tracers tested and, like several other sub­ ing. Also, the positive appearance of dye tracer at stances, were found to be highly adsorbed in the cores.