Page 101 - Enhanced Oil Recovery in Shale and Tight Reservoirs

88 Enhanced Oil Recovery in Shale and Tight Reservoirs

quickly be increased because gas is injected in the same low-pressure zone.
In other words, the pressure can be effectively increased. As the pressure is
increased, revaporization occurs. However, in the flooding mode, it takes a
long time for the pressure to transmit from the injection side to the produc-
tion side because of ultralow permeability.
Sheng (2015b) used a reservoir model to compare huff-n-puff gas injec-
tion with gas flooding. Orangi et al.’s (2011) gas condensate composition
was used. The dew point pressure is 3988 psi. The matrix permeability is
100 nD. The huff time and puff time are 100 days, and no soaking time is
used. The cumulative liquid oil produced from huff-n-puff and methane
flooding is shown in Fig. 4.10. It shows that more oil is produced from
huff-n-puff methane injection. The performance data are shown in
Table 4.1. It shows that the huff-n-puff injection produces 8.7% higher
liquid oil than the gas flooding. In the table, the net gas produced is the total
gas produced minus total gas injected in the huff-n-puff. Both gas and oil
produced are higher in the huff-n-puff injection. The revenue from oil
and gas production in the huff-n-puff case is also higher than that from
the gas flooding. The oil price of $100/STB and the gas selling price of
$4/MSCF are used in the calculation. The difference in capital investment
and facility and operation costs are not included. A discount rate is not taken
into account. If a discount rate is considered, the performance of huff-n-puff
will look even better than that of gas flooding, as the former liquid oil is
produced in the earlier time, as shown in Fig. 4.10.

Figure 4.10 Cumulative oil production from methane flooding and huff-n-puff
injection.