Abstract
The purpose of this study is to experimentally examine the effect of gas diffusion in the matrix blocks of light oil fractured reservoir subjected to gas injection. Experiments are performed in 1-D conditions on a chalk core saturated with a methane-pentane mixture in presence of different water saturation levels and with two diffusing gases: nitrogen and methane.
It has been found out that:
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Similarly to previous experiments performed without interstitial water, saturation profiles reveal a strong capillary end effect for nitrogen injection with an accumulation of oil near the fracture.
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The impact of water saturation on recovery depends strongly on the nature of the diffusing gas. In case of methane injection along the fracture, the faster the oil withdrawal at the fracture, the higher the water saturation level. In case of a nitrogen injection, the methane production is proportional to the hydrocarbon mass initially in place whereas pentane production remains unchanged.
In addition to that, in case of nitrogen injection, the variations of the differential pressure are pointing out discontinuity in the gas phase occuring between the fracture and the bulk of the porous medium. This gas build up is attributed to local change in the mixture composition induced by diffusion in the liquid.
