Determining the most representative reservoir model for the shallow depth salihli geothermal reservoir in Turkey using tracer test

Abstract

The tracer test has become one of the most important methods to determine the hydraulic connection between injection and production wells in a geothermal reservoir. Various chemicals such as fluorescein, radioactive chemicals, salts, and alcohols are used as tracers in geothermal systems. Breakthrough curves of chemical concentrations are matched with analytical models to identify the most representative reservoir model and to obtain important reservoir parameters such as swept pore volume, average fluid velocity, and dispersivity. In this study, we have used sodium fluorescein as a tracer to understand the reservoir characteristics of the Salihli geothermal field in Western Anatolia. The hydraulic connectivity between injection and production wells was identified. The study aimed to determine the most representative reservoir model for Salihli geothermal reservoir. The nonlinear least square method was applied to obtain matches between the analytical models and actual field data. The most representative model was found by evaluating the sum of the square residual. The study includes moment analysis, Dkystra-Parsons, and Lorentz coefficients for reservoir characterization. The study also used flow-capacity and storage-capacity relation to quantify reservoir characteristics for different parts of the reservoir. Fluid velocity in the Salihli geothermal reservoir changes between 2.8 and 19.2 m per hour. Calculated swept pore volume was found between 2 to 13 thousand cubic meter between injection and production wells.