Page 143 - Enhanced Oil Recovery in Shale and Tight Reservoirs

Optimization of huff-n-puff gas injection in shale and tight oil reservoirs 127

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 5.8 Near-wellbore block pressure when the huff-n-puff time are 100 days but
high rate (H100P100qx3).
increasing the rates, higher huff pressures and lower puff pressures near the
wellbore (fracture) will occur. Fig. 5.8 shows the near-wellbore pressure rea-
ches both the set maximum huff pressure and the set minimum puff pressure.
The oil recovery factor from this case is 23.3%, higher than that from the
case H300P300 (21.2%).
Furthermore, additional models are used to support the conclusion. If
the transmissibility is reduced, the near-wellbore block pressure will more
easily reach the set maximum injection pressure (7800 psi) during the huff
period and the set minimum production pressure (500 psi) during the puff
period. Even the huff time and puff time are short such as 100 days; the
oil recovery factor will be high or optimized. To prove that the transmissi-
bilities in the primary case (Primary) and the huff-n-puff case (H100P100)
are decreased by three times, the corresponding new cases, Primarytrans0.33
and H100P100trans0.33, are created. The near-wellbore block pressure in
the huff-n-puff case H100P100trans0.33 is shown in Fig. 5.9. It shows
that the pressure reaches the set maximum injection pressure during the
huff period and the set minimum production pressure during the puff
period. The oil recovery factors for the primary and huff-n-puff cases are
9.46% and 15.53%, respectively (see Table 5.4), resulting in the incremental
oil recovery factor 6.07%.