Tracer testing of flow between injection and production wells is an effective tool to map fluid flow pathways in a geothermal reservoir. Tracer concentration curves can be used to provide insight into projected thermal drawdown in the reservoir or thermal breakthrough of re-injected fluids, estimating inter-well volumes and flow geometries. Although radioactive tracers have been used in the past many tracer tests now use chemical tracers that are less hazardous to handle. Fluorescent organic compounds such as fluorescein and rhodamine-B, other fluorescent compounds such as naphthalene sulfonates and dissolved inorganic solutes such as potassium iodide (KI) and potassium bromide can be used as geothermal tracers. Nano-colloids have been suggested as ‘smart’ geothermal tracers. Tracer experiments were conducted using micro melamine resin rhodamine B particles with differing sizes ranging from 4 µm to 10 µm and conventional rhodamine B in a 2-D cross sectional model built from marble blocks that represents a low enthalpy liquid dominated geothermal reservoir. It has been observed that first arrival time of micro tracers was 4 times smaller than those observed in conventional rhodamine B tracer. The effect of injection rate, particle size and fracture geometry on micro particles was also investigated

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