Because of the need to quantify hydraulic fracture effectiveness, injection of chemical tracers in unconventional reservoirs has increased in popularity. Typical tracers are oil or water-soluble chemicals, which are injected into the formation along with the fracturing fluids. The tracers should invade a significant portion of the stimulated rock volume (SRV). The tracer backflow could shed light on the effectiveness of the hydraulic fracturing process and the SRV size.

Emulsion tracers and controlled-release tracers are the two tracer types currently used in the industry. This paper presents application, implementation and analysis of tracer flowback in unconventional reservoirs to determine individual stage flow patterns. The tracer flowback response is also of value in assessing the probable effectiveness of various enhanced oil recovery protocols in unconventional reservoirs. We present two field examples from Bakken and Eagle Ford formations to demonstrate the value of information obtained from the interpretation and analyses of tracer flowback.

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