PHASE-EQUILIBRIA IN OIL-WATER SYSTEMS

This article presents a selection of results obtained with the FHYD pr ogram. This software allows simulation of mixtures composed of petrole um fluids and water, with determination of the nature of thermodynamic ally stable phases (oil-gas-water-hydrate) under given conditions of t emperature and pressure, along with the quantity, composition and prop erties of these different phases. Additionally, the program can automa tically produce phase diagrams. Several examples of these have been in cluded here, ranging from binary systems (water-ethane) and ternary sy stems (water-methane-propane) to the most complex petroleum fluids. Th e presence of dissolved salts (sodium chloride) has also been taken in to consideration, as well as the calculation of conditions for the dep osition of solid salt. A number of petroleum problems are highlighted: water-saturated separator gas, water-saturated oil in reservoir condi tions, and oil in the presence of salt water. Estimates for the quanti ties and the composition of hydrates formed are compared with experime ntal data and with results obtained using other software. The FHYD pro gram can serve to give a more realistic representation of petroleum fl uid behaviour with more accurate determination of the transportation p roperties of their different phases, which is essential for the new ge neration of simulation models for multiphase pipeline design and opera tion.