Page 134 - Hydrocarbon Exploration and Production Second Edition

Reservoir Description 121

worthwhile to recover these liquids, and to leave the sales gas as a dry gas
(predominantly methane, CH 4 ). Note that the term wet gas does not refer to water
content, but rather to the gas composition containing more of the heavier
hydrocarbons than a dry gas.

6.2.3.5. Gas condensate
The initial temperature of a gas condensate lies between the critical temperature and
the cricondotherm. The fluid therefore exists at initial conditions in the reservoir as
a gas, but on pressure depletion the dew point line is reached, at which point liquids
condense in the reservoir. As can be seen from Figure 6.20, the volume percent of
liquids is low, typically insufficient for the saturation of the liquid in the pore space
to reach the critical saturation beyond which the liquid phase becomes mobile.
These liquids therefore remain trapped in the reservoir as an immobile phase. Since
these liquids are valuable products, there is an incentive to avoid this condensation
in the reservoir by maintaining the reservoir pressure above the dew point. This is
the reason for considering recycling of gas in these types of reservoir (Figure 6.21).
Gas is produced to surface separators which are used to extract the heavier ends of
the mixture (typically the C 5+ components). The dry gas is then compressed and
re-injected into the reservoir to maintain the pressure above the dew point. As the
recycling progresses, the reservoir composition becomes leaner (less heavy
components), until eventually it is not economic to separate and compress the dry

Figure 6.21 Gas recycling process.