The Patuha geothermal field is one of the few vapor-dominated geothermal systems in the world. Up to this point, brine reservoirs have not been confirmed in existing production wells. However, some wells in Patuha showed the presence of liquid, which is visually observed through the sampling port at the bottom during routine geochemical sampling, as seen in wells HND-A and HND-C. This condition has also been confirmed through the Tracer Flow Test (TFT), where the well has a dryness of 95%-98% with a slight liquid fraction. The results of PT logging surveys in both of these wells confirm the presence of a liquid column inside the wellbore. Unexpectedly, well HND-B, which appeared to be in dry-steam conditions at the surface, also shows the same condition. To obtain representative liquid chemistry data, further confirmation is conducted by running a liquid Downhole Sampling (DHS). The analysis results of water samples from wells HND-A and HND-C are secondary water products, with a predominant SO4 content. However, these two samples have slight differences in their chemistry. The sample from HND-A has a relatively lower pH value, higher levels of SO4, SiO2, and Fe, and lighter stable isotope values compared to the sample from HND-C. In contrast, well HND-B represents a different chemistry compared to the two previous samples, with the results of the anion diagram plot indicating a shift towards the Cl water area. This evaluation is carried out to gain an understanding of the processes and the origin of this water in the Patuha geothermal field.

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