Page 119 - Enhanced Oil Recovery in Shale and Tight Reservoirs

106 Enhanced Oil Recovery in Shale and Tight Reservoirs

Table 4.3 Effect of huff pressure.
P i [ 9088 psi P i [ 5000 psi

Primary H-n-P (A-PA)/ Primary H-n-P (B-PB)/
(PA) (A) PA (PB) (B) PB
Net gas produced 357.01 125.40 0.65 286.62 115.70 0.60
(MMSCF)
Oil produced (MSTB) 30.39 46.67 0.54 17.83 23.42 0.31
Oil recovery factor (%) 26.00 39.93 0.54 19.00 24.91 0.31
Revenues of produced 4.47 5.19 0.16 2.93 2.80 0.04
oil and gas (MM$)

Based on the base model described in Section 4.4, the dew point of the
gas condensate is 3988 psi, and the initial reservoir pressure is 9088 psi. In
principle, the huff pressure should not be higher than the initial reservoir
pressure to avoid fracture of the reservoir. Of course, it should be higher
than the dew point pressure. To test the effect of huff pressure, two huff
pressures of the initial reservoir pressure of 9088 psi and 5000 psi were
used. The results are presented in Table 4.3. It shows that for the huff pres-
sure of 9088 psi and 5000 psi, the incremental oil recovery of huff-n-puff
injection over primary depletion are 54% and 31%, and the incremental
revenues of produced oil and gas are 16% and 4%, respectively. These
results show that higher huff pressure is better.
4.9.2 Effect of puff pressure

To simplify the discussion of the effect of puff pressure, the puff pressure
should be below the dew point pressure (3988 psi w 4000 psi). Otherwise,
there is not liquid blockage issue. Table 4.4 shows that the gas produced in
the primary decreases with the puff pressure, because the production
drawdown becomes lower. However, the oil recovery increases with the

Table 4.4 Effect of puff pressure.
Puff pressure, Primary gas, Primary oil, Huff-n-puff,
psi MMSCF MSTB MSTB Inc. RF, %

500 357.01 26.00 39.93 53.6
1000 337.87 26.43 39.33 48.8
2000 285.84 27.97 38.81 38.7
4000 167.85 28.90 34.68 20.0
6000 85.13 15.27 25.32 65.8