A laboratory technique has been successfully developed to perform gas gravity drainage experiments under reservoir conditions in three dimensions, that is on cylindrical cores having both lateral and horizontal faces open to flow.

As an application to a light oil reservoir, a series of experiments has been performed on outcrop cores of various permeabilities, in order to compare the efficiency of methane or nitrogen injection. In a first step, cores were saturated with connate water and volatile reservoir oil and subjected to gravity drainage by injection of a rich gas in thermodynamic equilibrium with the oil phase. In a second step, either methane or nitrogen was circulated around the cores, yielding substantial additional recovery of liquids.

The results obtained clearly indicate that:

  • During the first step, recovery was essentially the same as in one dimension experiments (lateral faces coated).

  • Both methane and nitrogen exhibit fast and complete recoveries of light and intermediate components and appreciable amounts of the heavy end fraction. Kinetics of hydrocarbon recovery is strongly dependant on the nature and the injection rate of the gas injected.

  • An increase of pressure was investigated during gas injection, which exhibited a favourable effect on the heavier components recovery by methane. This influence was much less pronounced for nitrogen injection.

The laboratory experiments were interpreted with a fully compositional simulator. This confirmed the predominant role of vaporization and molecular diffusion.

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