Analysis of Injection-Backflow Tracer Tests in Fractured Geothermal Reservoirs

Abstract

Tracer tests have been an important technique for determining the flow and reservoir characteristics in various rock mamx systems. While the interwell tracer tests are aimed at the characterization of the regions between the wells, single-well injection-backflow tracer tests may be useful tools of preliminary evaluation, before implementing long term interwell tracer tests. This work is concerned with the quantitative evaluation of the tracer return profiles obtained from single well injection-backllow tracer tests. First, two mathematical models of tracer transport through fractures, have been reviewed. These two model are based on two different principles: Taylor Dispersion along the fracture and simultaneous diffusion in and out of the adjacent matrix. Then the governing equations for the transport during the injectionbackflow tests have been solved. Finally the results were applied to field data obtained from Raft River and East Mesa geothermal fields. In order to determine the values of the parameters of the models that define the transport mechanisms through fractures a non-linear optimization technique was employed.