FIG. 8 OIL RECOVERY
%
100
90
80
70
60
50
40
30
20
10
0
Indiana 1
Indiana 3
Initial Secondary Total
Fig. 5 shows temperature and pressure variation in the
field cases. Its four lines show five parts: Darcy flow, slippage flow, Fick diffusion, transition diffusion, and Knudsen (Kn) diffusion. Darcy flow appears in macropores larger
than 1,000 nm in diameter.
CO2 transport relies on diffusion in regions where microporosity has low permeability. Fig. 6 represents ideal gas
properties and illustrates real gases’ shift toward smaller
pore sizes.
Fig. 6 also shows how CO2 flow regimes are sectioned by
Darcy flow and non-Darcy flow at a 1 µm pore threshold,
Table 1 lists the permeability and
porosity properties for the three lime-
stone samples. Except for the Indiana
1 sample, permeability trends down
with increasing confining pressure as
measured by unsteady state experi-
ments. The method proved less suit-
able for the Indiana 1 sample, with an
expected permeability of around 200
md.
Time required for complete pressure equalization was 20 sec, making
the unsteady-state measurement for
Indiana 1 unreliable and leaving researchers to rely on permeability data
provided by the sample supplier.
When combining the permeability
and porosity properties from the supplier and the unsteady-state experiments, porosities of the investigated
samples were within 20%. Permeabilities, however, varied greatly.
MICP experiments demonstrated
the permeability-porosity relationship.
Total porosity can be divided into microporosity or macroporosity by contribution to permeability. Microporosity appears to have no
contribution to Darcy permeability, but its effect on flow and
transport should be further investigated.
Gas flow
Oil production in conventional reservoirs comes primarily
from their macropores. Large amounts of oil are left in microporosity regions. Gas-flow regimes helped evaluate the
possibility of recovery from micropores.
Equation 1 demonstrates how CO2 transportation varies.
Equation 2 shows the free path of gas molecules in a Lattice
Boltzmann flow simulation.
CO2 transportation in macropores can be described by
Darcy flow. Non-Darcy flow, especially diffusion, becomes
the dominant transportation in micropores
The authors relied on field data from 28 CO2 tests in Texas where CO2 transport patterns in pores of different scale
were studied. 9
PERMEABILITY, POROSITY; UNSTEADY STATE Table 1
Sample ––––––––––––––––––––––– Confning pressure; MPa ––––––––––––––––––––––––––––––
Indiana 2 Permeability, md 12. 52 12.04 12.06 11.99 11. 76
Porosity,% 22. 89 19. 21 23. 13 22. 56 22. 41
Indiana3 Permeability,md 5.96 5.95 5. 78 5. 69 5. 60
Porosity, 21. 14 22. 73 21. 15 21. 1 20. 54
Wisconsin Permeability,md 0.0233 0.0217 0.0196 0.0184 0.0176
Porosity,% 6. 61 8. 38 9. 28 8. 12 7. 38
CO2 fooding Table 2
Irreducible
Diameter, Length, Porosity, Gaspermeability, water
Core mm mm md saturation,
Indiana 1 25. 4 60 18 200 9. 48
Indiana 3 25. 9 65 19 9 8.97
OIL RECOVERY Table 3
First oil Second oil Total oil
Core recovery, recovery, recovery,
Indiana 1 66. 67 6. 67 73. 34
Indiana 3 39. 41 47.06 86. 47
