Tracer technology is an efficient and effective monitoring and surveillance tool with many useful applications in the oil and gas industry. Some of these applications include improving reservoir characterization, waterflood optimization, remaining oil saturation (Sor) determination, fluid pathways, and connectivity between wells. Tracer surveys can be deployed inter-well between an injector and offset producer(s) or as push-and-pull studies in a single well.

Tracers can be classified several ways. (a) Based on their functionality: partitioning and passive tracers. Partitioning tracers interact with the reservoir and thus propagate slower than passive tracers do. The time lag between the two types can be used to estimate Sor, to ultimately assess and optimize EOR operations. (b) Based on their carrying fluid: water and gas tracers. These can be used in IOR or EOR operations. All gas tracers are partitioning tracers and the most common are perfluorocarbons; they are thermally stable, environmentally friendly, have high detectability and low natural occurrence in the reservoir. On the other hand, water tracers are passive tracers and the most commonly used ones are fluorinated acids. (c) Based on radioactivity: radioactive and non-radioactive tracers. Selecting a tracer to deploy in the field depends on a number of factors including their solubility, fluid compatibility, background concentration, stability, detectability, cost, and environmental impact.

This paper provides an overview of various tracer applications in the oil and gas industry. These will include the single-well tracer test (SWCT), inter-well tracer test (IWTT), nano tracers, gas tracers and radioactive tracers. Their use will be highlighted in different scenarios. Field case studies will be reviewed for all types of tracers. Lessons learnt for all the applications, including what works and what does not work, will be shared. Specific cases and examples will include the optimization of waterflood operations, remaining oil saturation determination, flow paths and connectivity between wells, and IOR/EOR applications. The current state-of-the-art will be presented and novel emerging methods will be highlighted. This paper will showcase how the tracer technology has evolved over the years and how it shows great potential as a reservoir monitoring and surveillance tool.

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