Evaluation of Radioactive Tracer Surveys for Steam Injection Wells

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ABSTRACT The proper distribution of steam over the injection zone is critical to the efficient operation of a steamflood project. Many factors affect downhole steam distribution, such as differences in relative injectivity between perforations and gravity segregation of the phases. Surveys can be run in the wellbore to determine the steam injection profile. These profiles can then indicate which parts of the reservoir have been steamed and which may have been bypassed. Because steam consists of liquid and vapor phases, running profile surveys and interpreting the results are not straightforward. These surveys must be designed to generate information about the flow of both phases. Additionally, the survey results must be interpreted with a knowledge about the characteristics of the two-phase flow. In recent years, radioactive tracer surveys have become the most common method used to obtain steam profiles. The main emphasis has been on the use of inert radioactive gases for vapor profiling. Although radioactive tracer surveys are commonly used to obtain water or gas injection profiles, little is known about the reliability and accuracy of applying this method to profiling steam injection wells. This paper presents the results of field testing and evaluation of vapor phase profile surveys using radioactive Krypton and Xenon gas tracers. Emphasis is given to surveying (or logging) procedures and data analysis methods and to determining the reliability and accuracy of vapor injection profiles. Existing data analysis and interpretation methods are reviewed and a new, automated method is presented that gives more consistent and reliable evaluation of tracer measurements. The accuracy of tracer measurements and resulting vapor injection profiles are discussed. Factors affecting repeatability of tracer measurements, such as tracer radiation intensity, wellhead steam conditions, and well completion are also discussed.