Determination of Flow Connectivity and Heat Exchange Surface in Fractured Media Using Multicomponent Tracer Test

Abstract

Multicomponent tracer tests are often used to understand advective and diffusive processes in fractured permeable media, and to determine the heat exchange capacity and spatial flow connectivity of fracture network. This study explored the behaviors of tracers, including chloride (inert tracer), lithium ion (sorptive tracer) and Rhodamine123 (thermally degrading tracer), in single-fracture column specimens under the temperature conditions of the hot dry rocks in the Gonghe Basin, China. It was found that adsorption ratio of Li+ is in proportion to the concentration of rock powders representing the absorbent surface area. Both adsorption ratio of Li+ and degradation ratio of Rhodamine123 increased with the temperature. The relative retardation of the sorptive and thermally degrading tracer concentration signals to the inert tracers was used to investigate the fluid/rock surface area and the temperature variation. The laboratory tests and analyses showed that application of multicomponent tracers proposed in this study can estimate the flow connectivity and monitor transient heat exchange capacity in fractured geothermal reservoirs.