Page 128 - Enhanced Oil Recovery in Shale and Tight Reservoirs

114 Enhanced Oil Recovery in Shale and Tight Reservoirs

Figure 4.30 Oil volume changes with time in huff-n-puff methanol injection.

4.10.2 Swelling by a solvent
Methanol can solubilize the liquid condensate and dissolve gas. Fig. 4.30
shows the oil volume in the model consistently increases with cycles.
Since oil is constantly produced, the original oil volume must decrease;
the increase in oil volume is due to methanol solubilization. The oil volume
in place is actually a mixture of solvent and hydrocarbons.
Although solvents displace some condensate near the wellbore, they also
occupy the space that is occupied by the condensate. Thus, they cannot
effectively increase gas permeability. However, they generally have lower
interfacial tension (IFT) with the condensate. It is easier for them to flow
back with the condensate with lower IFT. Solvents may also dissolve wax
or asphaltene blockage.

4.10.3 Changed phase behavior
Gases and solvent may convert a contacted condensate to a more volatile
fluid, reducing the dewpoint and liquid dropout. For example, when Fluid
A is added with 15% mole fraction of methane, ethane, propane, and CO 2 ,
the dew point and dropout are reduced (Fig. 4.31). When methane or
ethane is injected, the dew point of the earlier mentioned Fluid B is reduced
(see Fig. 4.32).