Monte Carlo Model Simulations of Tracer Tests to Determine Fracture Aperture Size Range in an Anisotropic Geothermal Reservoir

Abstract

The predictive modeling of flow and transport processes in geothermal reservoirs is challenging due to the complex nature of fracture networks. Tracer tests are traditionally used to characterize such reservoirs for sustainable injection and production strategies. Interpretation of tracer tests for acquiring correct flow parameters is usually carried out using oversimplified mathematical models. The analytical approaches particularly developed for modeling tracer tests in porous and fractured media provide uniform flow parameters that are not suitable for detailed geothermal reservoir characterization due to anisotropy and macro-dispersion. Moreover, numerical dispersion parameters that represent the macro-dispersion of a tracer are usually not pertinent. In this study, a tracer test is analyzed to characterize and predict the thermal breakthrough time of a geothermal reservoir located in western Turkey. A new analytical model particularly developed for the analysis of tracer tests conducted in porous and fractured reservoirs is coupled with Monte-Carlo simulations acquiring effective parameters from well-to-well data to obtain fracture aperture values in an anisotropic fractured medium. Subsequently, fracture aperture values are evaluated by analyzing mud-loss data provided by well-logs and compared with the analytical model results. The objective is to estimate the fracture aperture size and to inspect the relationship between anisotropic flow, fracture aperture orientation, and longitudinal dispersivity in a deep geothermal reservoir. Results demonstrate that the anisotropic flow paths have an impact on the macro-dispersivity both in longitudinal and transversal directions.