Page 112 - Enhanced Oil Recovery in Shale and Tight Reservoirs

Huff-n-puff injection in shale gas condensate reservoirs 99

Fluid B described in the preceding section is used in the model; the bi-
nary interaction parameters among components are from Bang et al. (2010).
The initial reservoir pressure is 7800 psi. The reservoir is under 5 years of
primary depletion before huff-n-puff. During the huff-n-puff injection,
the injection pressure is 7800 psi which is above the dew point pressure.
When the pressure in the well block (2,16,1) adjacent to the hydraulic frac-
ture reaches the injection pressure of 7800 psi, the operation is switched to
the puff period. The puff pressure is 1200 psi. When the pressure at the
Block (2,16,1) approximately reaches 1200 psi, operation is switched back
to the huff period again. Such process is repeated for 10,585 days or 29 years.
For gases, the huff time is 175 days and the puff time is 920 days. For meth-
anol, the huff time is 575 days and the puff time is 1500 days. For isopropa-
nol, the huff time is 775 days and the puff time is 1750 days. No soaking time
is used.
In this section, the recovery factor (RF) in % at any time is calculated us-
ing this equation:

Total original hydrocarbon moles in placeeremaining total hydrocarbon moles in place
RF ¼ *100
Total original hydrocarbon moles in place
Using moles of components makes the RF independent of the reservoir
or surface pressure and temperature conditions. The recovery factors for
different gases and solvents are shown in Fig. 4.21. Similar to those results

Figure 4.21 Total hydrocarbon recovery factors versus time from different operation
schemes.