Determination of Water Content For Hydrate Formation in Gas-Dominant Systems Using a Multiphase Flash Algorithm

Accurate prediction of hydrate formation and dissociation in natural gas systems is essential for multiphase flow applications and carbon capture and storage technologies. This work presents a modified simultaneous flash-with-stability formulation to calculate the gas-phase water content under incipient hydrate conditions. Given P, T, and the dry-gas composition, we determine the water content while enforcing β_H = 0. Hydrates are modeled with the van der Waals–Platteeuw framework, while the fluid phase is described using PC-SAFT and Modified Peng–Robinson equations of state. The methodology was validated against literature data and new measurements for systems containing CH₄, CO₂, and C₂H₆. Results indicate that PC-SAFT provides superior accuracy, particularly in low-moisture regimes. P–T and P–y_w maps quantify the effects of composition and humidity. By determining the water content at incipient hydrate within a stability-checked flash, our method reduces numerical issues near phase boundaries and provides a practical tool for risk analysis and offshore system design.