In gas-condensate reservoirs, a major challenge is to avoid the drop-out of the heavier fractions, which represent the rich part of the gas, responsible for great part of its heat capacity and, consequently, its price.

A widely used prattice to keep the reservoir fluid above its few point pressure is the injection of produced lean gas into the reservoir. This technique is known as gas cycling. As the lean gas is injected in the reservoir, the overall fluid composition is changed and so does its dew point and phase envelope. Furthermore, the rate of pressure decline fo the reservoir depends on the fraction of the produced gas being injected.

We present a coherent thermodynamic analysis of the effects of lean gas injection fo two Brazilian gas/condensate reservoire through the determination of the phase behavior of injected/original gas mixtures.

The accuracy of the thermodynamic model employed is verified through the comparison of the model predictions with laboratory data.

The results obtained from this analysis are used to determine the maximum amount and optimal composition of lean gas to be injected fo a gas/condensate reservoir in onler to change its composition and shift the phase envelope to a point where the liquid droprout can be eliminated or minimized during the isothermal deletion of the reservoir.

The results can also be used to optimize the operation of gas pipelines and production equipment and facilities.

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