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The Green-Kubo formalism for evaluating transport coefficients by molecular dynamics has been applied to multicomponent mixtures of flexible, multicenter models of linear and branched alkanes and nitrogen and helium in the gas phase and in the liquid phase. Simulation results on binary systems are summarized and trends in prediction using simple but realistic molecular models are shown. New simulation results of N2–n-pentane agree with experiment with a maximum deviation of 36%, the greatest error being for pure n-pentane. Methodological aspects of simulating multicomponent systems with trace components are studied, varying the system size and molecular interaction potentials. It is shown that mixtures are treated representatively even when only one to two molecules of a species are present in the simulated system, unless there is an extreme degree of self-association. It is demonstrated that molecular dynamics may predict quantitatively (7% and 11% deviation) the viscosity of a seven component “synthetic” natural gas.

A new compositional model is proposed to improve the prediction of phase behavior and physical properties of oil reservoir effluents. This work is based on a very classical and easy-to-handle cubic equation of state (EoS) coupled with a performing group contribution method devoted to the estimation of binary interaction parameters. The proposed model is compared to other published methods on the basis of laboratory data on real fluids, including pressure/volume/temperature (PVT) measurements and slim tube experiments. The method developed in this work shows enhanced results on a large range of pressure and temperature.

This paper presents an experimental methodology that allows a sensitive determination of the onset and rate of deposition in asphaltene-containing fluids when the pressure, temperature, or fluid composition are varied. This determination is inferred from pressure drop measurements across a capillary tube in which the fluid is injected at a constant flow rate and at specified conditions of temperature, pressure and composition. When the conditions for deposition are met the pressure drop across the capillary tube is no longer stationary but increases with time as a result of the buildup of a deposition layer on the tube walls. In the experimental set-up that has been constructed, the fluid composition is controlled by co-injecting the various fluid components into the capillary by means of different pumps. This setup has been utilized to determine, at some given temperature and pressure, the deposition envelope of systems made of crude oil, solvent (xylene) and precipitant (heptane). The measured deposition points coincided with bulk flocculation thresholds determined by a conventional light transmission method. The light transmission method was, however, difficult to for fluids with a very low asphaltene content, whereas the proposed method was efficient for fluids containing as low as 0.04 wt.% asphaltenes. The rate of deposition was observed to increase with the distance from the deposition onset. Reversibility of deposition was significant only when the asphaltene-containing fluid was returned to conditions remote from those of the deposition onset.

The heavy oils from Venezuela and Canada are being considered with a growing interest due to some promising large reserves. From many case histories, the implementation of a cold production scenario has been able to produce this oil at a reasonable cost due to an improved ultimate oil recovery higher than expected. A foamy oil behaviour has been postulated to partially explain the phenomenon. A series of 5 experiments has been performed to carefully assess the hypothetical foamy oil effect on the ultimate recovery during the natural depletion process. Two parameters were studied: the gravity force impact and the depletion rate in order to upscale these data to the field application. A highly permeable long core was used with heavy reservoir oil (9°API). The porous media was set at initial reservoir conditions (60 bar(g), 49°C) with irreducible water saturation for each of these experiments. The cold production process by natural depletion was implemented at constant depletion rate with an accurate monitoring of the back-pressure regulator. Comparing laboratory experiments conducted in horizontal or vertical flow direction at low depletion rate, gas gravity segregation effect seems to already improve the oil recovery at the laboratory scale although it is difficult to demonstrate the presence of a continuous gas phase. These results could indicate that the nucleation of the gas bubbles to create a gas phase is a very slow process due to the oil viscosity effect, above 1500 cP at reservoir condition in the presented case. The gas bubbles remain partly trapped within the oil and move with the liquid phase at least up to the threshold saturation. At field scale, corresponding to much lower depletion rate, this effect may be more significant particularly in unconsolidated sands where the vertical permeability is very high. The ultimate recovery defined at laboratory scale appears to be significantly dependent on the depletion rate as expected and already reported in the literature. It has however to be noted that the mechanism, developed at high rate at the laboratory scale, is not applicable to field production. At low depletion (2.5 bar/d), about 19% IOIP were recovered whereas 42% IOIP were recovered at 12 bar/d and 45% IOIP at 25 bar/d. The critical pressure at which free gas production occurred was estimated for each experiment. A pseudo 4.5% critical gas saturation was determined for the low depletion rate whereas a high depletion rate yielded 25.5% critical gas saturation.

ELDFISK field, located in Block 2/7 of Norwegian offshore 20 km South of EKOFISK field, is producing from fractured chalk formations called EKOFISK,TOR and HOD. The paper presents the successive modelling methodology used from 1982 to estimate its performance under natural depletion as well as improved oil recovery processes as a function of the available field information and the improvement of the simulators.