Page 108 - Enhanced Oil Recovery in Shale and Tight Reservoirs

Huff-n-puff injection in shale gas condensate reservoirs 95

with the recovery factor of 54% followed by 25.1% from methanol injection
and 18.4% from methane.
However, different volumes of gases and solvent are injected during the
same huff-n-puff time. Fig. 4.16 shows the total hydrocarbon recovery
factors versus their injection pore volumes. It shows that their performances
rank the same as those in terms of huff-n-puff time. Further for a proper
comparison, their difference costs should be taken into account. Fig. 4.17
compares their performances in terms of costs. When calculating the cost,
these prices are used: $3.17/Mscf for methane, $0.88/gal. for methanol,
$1.35/gal. for isopropanol, and $4.15/Mscf for ethane according to
McGuire et al. (2016). Because it is a small core scale, the absolute costs
are low. These costs should be interpreted at their relative values.
The above comparisons are based on the total hydrocarbons, and the
performances are ranked as ethane, methanol, methane. To understand their
EOR mechanisms, the recovery factors of individual components should be
compared. Fig. 4.18 shows that methanol has good recoveries for methane
and butane, but not as good for heptane and decane. The injected methane
hardly produces the original methane (0.2%, not visible in the figure).
In other words, the produced methane is almost the same amount as the
injected methane. But methane recovers higher volumes of butane, heptane,
and decane than methanol. Since the condensate dropouts in the core are

Figure 4.16 Total hydrocarbon recovery factors in different injected pore volume.