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Tracers are used in well to well tests to gather data about the movement and saturation of fluids and hydrocarbons in the subsurface. Radioactive tracers can be used to gather data about water or gas. This article discusses some of the commonly used radioactive gas tracers. Several authors report the use of radioactive gas tracers in oilfield applications. The tracers most frequently applied have been tritiated methane, tritiated ethane, and 85Kr.
Interwell tracer tests are widely used. This article reviews some of the studies reported in open literature. The selection introduces different problems that have been addressed, but the original papers should be studied to obtain a more detailed description of the programs. The Snorre field is a giant oil reservoir (sandstone) in the Norwegian sector of the North Sea. Injection water and gas were monitored with tracers, 18 and the resulting tracer measurements are discussed in this page.
A successful well to well tracer test is more than selecting the right tracer. It involves determining the appropriate timing, designing the field test, and collecting and analyzing the samples. A well designed sampling program will produce high quality tracer-response curves for further interpretation. The timing for tracer injection depends on the information that is requested. Normally, it is desirable to inject the tracer early in the injection process to obtain information as soon as possible and be able to take the necessary actions to optimize the production strategy.
Selecting the appropriate tracer, and understanding the information gathered during a well to well tracer test requires consideration of how various tracers interact with, and therefore flow, through reservoir rock. When tracers are flowing in the reservoirs, it is normally a requirement that the compounds follow the phase they are going to trace. The best example of a passive water tracer is tritiated water (HTO). The HTO will, in all practical aspects, follow the water phase. For gas tracers, there are no known passive tracers.