SOLID-FLUID EQUILIBRIA IN MODEL SYSTEMS FOR HYPERBARIC RESERVOIR FLUIDS

摘要

Nowadays there is a duality regarding the end of the petroleum reserves. On one hand the consumption of petroleum and derivatives is increasing, on the other hand the development of the drilling technology allows us to find and exploit petroleum reservoirs at deeper depths. Due to the higher depth of these new reservoirs, their characteristics regarding pressure, temperature and composition are different from the traditional reservoirs. In these hyperbaric reservoirs the temperature and pressure are higher than the ones found in the traditional reservoirs and the reservoirs fluids have a high percentage of methane but also relatively large amounts of heavy alkanes reaching up to C60. It this high percentage of heavy alkanes that causes large problems during the exploration and production of these reservoirs fluids, since" wax precipitation can occur when the temperature and pressure conditions change. So it is important to know the phase behaviour of these kind of mixtures. Adequate thermodynamic models should be available to describe the phase behaviour of the system under consideration. In the past, the wax formation problem was mainly handled on the basis of empirical models. In recent years, more effort has been spent on the development of adequate thermodynamic models. One of the problems is that it is not known if the wax precipitates as a mixed crystal or if every component precipitates as a pure solid. A general problem is the scarcity of experimental data on the phase behaviour of well-defined multicomponent mixtures. Abundant experimental data are available on systems with either only one solute or two solutes that are known to precipitate as independent pure component crystals. Further, experimental data sets are available on binary systems possibly forming mixed crystals in the absence of a solvent. Other data sets of real reservoir fluids and fuels do not allow us to make a clear distinction between different mechanisms involved in the solid precipitation, due to characterization procedures and experimental accuracies. To bridge the gap between different data sets available in the literature, it is desirable to have phase equilibrium data for systems of one solvent and a few solutes that are known to form mixed crystals in at least one of the binary subsystems. Some data sets are available for these kind of systems. In this presentation, experimental results of the solid solubility in the ternary system composed of methane, triacontane and tetracosane for 11 concentrations are presented. Additionally, experimental data on the phase behaviour of 13 mixtures of methane and triacontane are given. Also de results of an evaluation of the performance of different E.O.S. models and mixing rules will be presented.