The determination of hydrocarbon saturation in oil reservoirs plays a significant role in the management and selection of enhanced oil recovery (EOR) methods. Tracer tests to measure residual oil saturation in the near-wellbore zone (SWCTT) before and after EOR involve injecting tracer into the reservoir and monitoring its recovery for quantification and analysis. The most important issues to address when planning SWCTT are the proper selection of primary tracers with a predetermined shut-in time for controlled secondary tracer generation. Based on the extensive field data, it is known that from 10 to 50 % of the primary tracer should be hydrolyzed at the wellhead during reverse production in order to be able to detect tracers during reverse production and best interpretation of production concentration profiles in the next stages of the study. In this regard, this paper proposes a new analytical approach to determining the well shut-in time during SWCTT after injection of tracer banks in target oil saturation intervals. This method was verified at the object of surfactant-polymer flooding (oilfield in Eastern Europe) and showed its efficiency, as evidenced by the obtained tracer production profiles, on the basis of which the average value of residual oil saturation (0,109) after injection of surfactant-polymer composition was calculated, which is a successful result for chemical flooding.
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