DETERMINATION OF THE MOISTURE CONTENT OF A METHANE AND CO₂ MIXTURE IN UNDERWATER PROCESSING SCENARIOS

The production of oil and natural gas from Brazil's pre-salt reservoirs poses significant operational challenges due to high pressures and low temperatures, elevated gas-to-oil ratios, and the substantial presence of carbon dioxide (CO₂) in the produced streams. In this context, accurate determination of water content in natural gas is essential to mitigate issues such as corrosion, reduced operational efficiency, and, particularly, hydrate formation, which can jeopardize flow assurance in subsea systems. This work aims to experimentally determine the water content in methane (CH₄) - CO₂ gas mixtures under conditions representative of subsea processing. Measurements were performed using a Quartz Crystal Microbalance (QCM), chosen for its high sensitivity in detecting trace amounts of water vapor. Experiments were conducted in a high-pressure equilibrium cell with strict control of temperature and pressure, spanning from 263.2 K to 318.2 K and 49.3 bar to 568.4 bar, respectively. Results indicated water contents ranging from 40.9 ppm to 1906.7 ppm, with repeatability analysis showing standard deviations of 0.12% to 22.1% and an average of 6.1%, indicating good consistency in most measurements. Expanded uncertainty analysis showed absolute values ranging from 0.0 ppm to 241.3 ppm, with an average of 14.5 ppm (equivalent to 1.4%). These results reinforce the overall reliability of the measurements. The experimental data showed good agreement with literature values, validating the developed apparatus and methodology. This study advances thermodynamic modeling of CH₄ – CO₂ – H₂O systems and provides valuable input for the development of predictive tools for flow assurance and natural gas processing in offshore environments.