Our lab is investigating and testing thermally stable tracers that will help geothermal energy producers to assess the surface area available between injection and production wells. Adsorption of solutes onto mineral surfaces is a function (in part) of how much surface area/fluid interaction occurs in a system and the rock temperature. Sequential tracer breakthrough curves may provide a tool to indicate changes in available surface area and rock temperature profiles. Research results are presented that show how the use of tracers that interact (i.e. sorb) with the surface of the geomedia can help to refine the estimation of the available effective heat transfer area. A series of high temperature miscible displacement experiments with the fluorescent dye, safranin T, through media with different size fractions of Ottawa sand demonstrates the relationship between the retardation of a reactive tracer relative to a conservative tracer and the amount of surface area that the fluid encounters. Thermal characteristics of the tracer and temperature effects on its retardation through the media are presented, as well as a discussion on analysis, detectability, and availability of potential reactive tracer candidates for field applications.

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