Fracture Dispersion Effects in Tracer Analysis

Hydraulic dispersion in porous media and in fracture networks results in the spreading of the timedependent tracer signal. In geothermal reservoirs the wellbore often intersects fractures that are separated by tens or even hundreds of meters. The mixing in the wellbore at those separated fractures is also a source of dispersion, since tracer signals sampled at the wellhead are a mixture of the individual tracer signals arriving from all fractures intersected by the production wellbore. The dispersion in reservoir fractures is most heavily dependent upon mixing and spreading at fracture joints. In this paper we discuss the relevant reservoir and wellbore dispersion phenomena and compare calculated tracer signals with measured tracer data for a case of low flow rates and widely spaced fractures.