A new downhole sampler, GTFSampler, is designed to collect in-situ geothermal fluids and preserve the conditions of the sampling depth. The GTFSampler is mainly composed of a stainless sampling cylinder and a gas driven shut-in valve, which are hosted in an equipment protector. The sampler assembly connects to a stainless tube for hoisting in a borehole and switching the shut-in valve by changing the inner pressure of the stainless tube on surface. Selected gas (e.g., N₂ or noble gas) is pre-filled to the sampling cylinder at a fixed pressure before sampling. The GTFSampler is also equipped with a traditional mercury maximum thermometer. The comparison between the measured temperature and calculated thermodynamic equilibrium temperature from saturation degree of minerals is used to verify the representativeness of downhole sample collection, on-site sample separation and laboratory analysis.

In the borehole IC-19 deployment in Chingshui geothermal field, Ilan, Taiwan, the measured temperature at 800 m are ca. 190∼198 °C. Three downhole samplings were conducted in this study, i.e., the first and second samplings were deployed in discharged borehole condition and the third sampling in closed borehole condition. The first and second samplings showed that the theoretical equilibrium temperature calculated by geochemical modeling from fluid composition is very close to the measured temperature at the sampling depth. However, no convergence solution for equilibrium temperature is obtained for the third sampling, indicating certain interference in geothermal water quality by the natural convection inside the borehole as the control valve is closed. In summary, the GTFSampler and its corresponding sampling procedures successfully collect the downhole geothermal fluids.