This paper describes a systematic methodology to extract as much information as possible from inter-well tracer tests. Interwell tracer testing has been used extensively in Norway and world-wide the last 2-3 decades and is proven as an efficient technology to map well-to-well communication and sweep, and to evaluate the effect of water and gas injection projects.

Significant information can usually be extracted from tracer curves, in addition to the immediate injector-producer communication available upon first tracer breakthrough. Improved tools and methods, such as residence time distribution (RTD) analysis, can quantify how effective water and gas floods displaces water, and reveal flow paths and channels prior to infill-drilling, polymer blocking etc.

However, prior to interpretation of tracer data, it is essential to remove uncertainties due to water or gas re-injection, commonly applied to reduce discharge to the environment and save scarce water-resources. However, recirculation of produced water and gas can be seriously misleading when tracer data are interpreted, because tracers will be re-injected with re-injected water or gas.

In this paper we show how the background tracer concentration due to re-injection can be removed in a systematic and unambiguous manner. The methodology is tested on data from tracer campaigns in two field cases. The tracer data from the field cases are subsequently used to evaluate water flooding sweep and reservoir heterogeneity using residence time distribution (RTD) analysis. The field case results show that the method is well suited to obtain quantitative flow pattern information from tracer data, and provides an effective tool for reservoir engineers that use tracer data to extract information about reservoirs.

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