The work presents results of experimental and analytical investigations enabling to comment on some aspects of phase transformations taking place in natural hydrocarbon systems during the development of deposits.

The following issues have been considered:

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    A new phenomenon in phase transformations of gascondensate systems and its experimental investigation;

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    Experimental investigation of the influence of different composition gases solubility in hydrocarbonoceous condensates on the exploration of gascondensate pools;

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    Impact of the porous medium on the evaporability of condensate while affecting it by "dry" hydrocarbon gas.

The main text.

a) A new phenomenon in phase transformations of gascondensate systems and its experimental investigation.

There has been also considered a phenomenon of retrograde condensation and evaporation with its further physical explanation which are of great interest during the development of gascondensate deposits.

As has been shown in [1–3, and others], a partial evaporation of the liquid condensate at constant temperature and pressure can be realized by the replacement of the gas phase of the system by gases that are highly soluble in condensate (e.g., "dry" hydrocarbon gas). It has also been shown that the amount of condensate evaporated under the influence of dry hydrocarbon gas increases with pressure, mechanism of this process explains by solubility of gas in liquid[3].

At the same time, one can state that when any liquid is compressed by gas, the critical temperature of which is higher than that of the system, gas molecules are dissolved in the liquid. Consequently, the forces of intermolecular interaction in the liquid are diminished and the liquid evaporates at the temperature, which is lower than the temperature of evaporation of the individual substance [4].

We conditionally distinguish two types of interactions responsible for the evaporation and condensation of the gas-condensate system. In the first case, evaporation (condensation) is a response to changes in thermal characteristics of molecules affected by temperature and pressure of the system. In the second case, the process is related to the dissolution of gas molecules in the liquid.

Thus, the retrograde process may be explained as follows. System near point 1 (Fig. 1) is in the gas phase. If we increase pressure at a constant temperature, the system should normally condensate beginning from point 2. In this case, both scenarios will develop. However, the first scenario will be more active, because the liquid contains some gas. As a result, the pressure of the onset of condensation at the given temperature will be higher than the respective value for individual substances. Condensation is accompanied by increase in pressure and the process slows down as point 3 is approached, because the quantity dissolution gas in liquid accelerates with pressure. Condensation ceases already at point 3, because the amount of dissolved gas becomes high enough. At the same time, the intensification of the second type of interaction triggers an anomalously active evaporation of the liquid. Thus, under increasing pressure, the retrograde evaporation continues with the active participation of the second scenario beginning from point 3 and terminates with the complete evaporation of the condensed liquid at point 4. Above this point (including point 5), the system occurs in the one-phase (gas) state.

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