Page 120 - Enhanced Oil Recovery in Shale and Tight Reservoirs

Huff-n-puff injection in shale gas condensate reservoirs 107

puff pressure because higher puff (production) pressure results in less liquid
oil dropout and then more oil produced.
For the huff-n-puff injection, the liquid oil produced decreases with the
puff pressure, indicating that the lower production drawdown is less beneficial
because less gas or energy is injected to boost the production of gas and liquid
condensate. Therefore, the incremental oil recovery of huff-n-puff injection
over the primary depletion decreases with the puff pressure.
To further discuss the effect of puff pressure, a case of 6000 psi puff
pressure is added in the table. The primary gas production, primary oil
production, and huff-n-puff oil production are all the lowest. This also
implies that wells in a gas condensate reservoir should be produced below
the dew point pressure.

4.9.3 Effect of cycle time
Table 4.5 shows the effect of cycle time. Here the cycle time is equal to the
huff time and the puff time. As the cycle is shorter, more net gas is produced.
However, the total liquid oil produced peaked at 100 days. The revenues
from produced oil and gas also peaked at 100 days, implying that produced
oil has higher economic value.

4.9.4 Effect of soak time
In Table 4.6, 100-0-100 means 100-day huff, 0-day soak, and 100-day puff.
The first number is the huff time, the middle soak time, and the last
puff time. The results show that when the first 100 days are split into 50-
day huff and 50-day soaking, oil recovery and the revenues from oil and
gas produced become lower, except the net gas produced. This means soak-
ing is not effective. The benefit of soaking is to facilitate the injected gas to

Table 4.5 Effect of cycle time.
200 d 100 d 50 d 25 d
Total gas produced 2232.2 3133.7 3783.1 3814.4
(MMSCF)
Gas injected (MMSCF) 2161.6 3008.3 3621.5 3572.0
Net gas produced 70.6 125.4 161.6 242.4
(MMSCF)
Oil produced (MSTB) 43.816 46.666 44.668 40.891
Oil recovery factor (%) 37.49 39.93 38.22 34.99
Revenues of produced 4.664 5.1682 5.1132 5.0587
oil and gas (MM$)