Predicting water content in hydrocarbon production systems

The formation of hydrates in hydrocarbon mixtures presents challenges in industrial sectors, necessitating the determination of water content, in addition to identifying pressure and temperature conditions that ensure a hydrate-free zone during production, processing, and transportation. Different models have been suggested to predict the minimum water content, required to avoid hydrate to form. However, the capabilities of these models for accurate representation of these variables need to be evaluated. In this study, water content measurements of liquid propane in equilibrium with liquid water or hydrates were determined across a range of pressures (up to 8.274 MPa) and temperatures (276.15 to 313.15 K) using three different measurement methods: a quartz crystal microbalance (QCM), a silicon oxide-based hygrometer and a novel method developed by Burgass et al. (2021). The new method and QCM measurements exhibited good agreement. The fluid phase behaviour of the propane-water system was modelled using the simplified Cubic-Plus-Association (sCPA-SRK) equation of state, which provided accurate predictions. Deviations of 4.5% were observed between the experimental measurements and the sCPA-SRK model within the temperature range of 276.15 to 313.15 K. Hydrate-forming conditions were modelled using the van der Waals and Platteeuw's solid solution theory, showing good agreement with the literature data. For ethane, a model based on the sCPA-SRK equation of state coupled with the van der Waals' classical mixing rules and van der Waals’ and Platteeuw's solid solution theory was employed to determine the minimum water content required for hydrate formation. The model achieved an average absolute deviation of 9.25% when compared to experimental measurements obtained from this study and existing literature. Additionally, the model accurately predicted ethane solubility in the aqueous phase and hydrate dissociation points. The study also investigated methane, the primary component of natural gas supply, and provided water content measurements for 9 hydrocarbon mixtures. The sCPA-SRK equation of state was used in conjunction with the van der Waals' classical mixing rules and the van der Waals’ and Platteeuw's solid solution theory to determine the minimum water content required for hydrate formation. The model achieved an overall average absolute deviation of 5.2%