Monitoring of gas and fluid transport from the hydrothermal reservoir to the Cerro Pabellón geothermal plant; international validation of analytical protocols

The geothermal heat extraction of binary type plant and its lifetime can be optimized through fluid monitoring of its gas and the natural system gas discharges. In order to present a novel gas monitoring tool for geothermal exploration and decision-making production, this research at Cerro Pabellón, Chile, since its internationally celebrated opening in 2017, demonstrates that the compositional characterization of gas and CO ₂ -rich phases is beneficial for deepen understanding of the gas compositional array and associated physico-chemical processes produced from wells drilled into high-enthalpy geothermal systems elsewhere. The gas phase, studied through 5 years of direct gas condensate sampling and first-time application of a Principal Component Analysis (PCA) factor as Uniform Manifold Approximation and Projection (UMAP), showed two clear trends in gas mixture fluctuations: cooling as an Apacheta-like gas mixture hydrothermal reservoir with fluctuations between reducing-weakly oxidizing conditions. The equilibrium gas geothermometers obtained by studying the gas chromatography results of CO ₂ -rich (> 96.0%) gases show a liquid-dominated system circuit-reservoir/in equilibrium with steam at a temperature of 225–350 ºC (Md = 252 ± 78°C) and oxidation variations (Md= -3.43 ± 0.64 RH), resulting from a complex cooling process that is distinct at the segments of the vapor separation lines (C, F, J, M) until reaching 140–160°C at the plant steam/brine separators. The monitoring data show that cooling of the vapour phase causes an increase in oxidation state (RH) and vapour fraction (%). When the condensate fraction increases during cooling (> 80%) and subsequent HCO ₃ ²⁻ dissolve in the condensate as liquids, this thermal effect can be detected by the enrichment of [Ar] content (ppm) and lower N ₂ /Ar ratios in gas samples; such compounds in equilibrium with CO ₂ -rich fluids should be monitored and controlled in geothermal plants to improve long term maintenance and binary type power plants sustainability by combining condensate liquid survey.