Page 142 - Enhanced Oil Recovery in Shale and Tight Reservoirs

126 Enhanced Oil Recovery in Shale and Tight Reservoirs

10,000

Pressure: PRES Block 2,16,1 (psi) 6,000
8,000

4,000

2,000

0
2015 2020 2025 2030 2035 2040
Time (Date)
Pressure: PRES Block 2,16,1
Figure 5.7 Near-well block pressure in H300P100.

switched to the huff mode. Thus, the effective production is lost. To support
this statement, case H300P200 is simulated. The oil recovery factor is
increased to 19.49%.
Will the oil recovery increase when the puff time is further increased
from 300 days? Three more cases, H300P350, H300P450, and
H300P600, where the puff time is extended to 350, 450, and 600 days
are simulated. The oil recovery factors are 20.95%, 20.57%, and 20.12%,
respectively (see Table 5.4), all lower than that from H300P300! The
near-wellbore block pressures during the huff-n-puff are slightly lower
than those in H300P300 (data not shown here to shorten the presentation).
Also, the oil rate after 300 days is very low; thus the extended production is
not effective.
From the above discussions, we may conclude that the optimum huff
time is so long that the near-wellbore pressure reaches to the set maximum
huff pressure, and the optimum puff time is so long that the near-wellbore
pressure reaches to the set minimum puff pressure.
To support the above conclusion, based on the case H100P100, another
case H100P100qx3 is simulated. In this case, both the maximum injection
rate and the maximum production rate are increased by three times. By