FIG. 5 CO2 TRANSPORT PATTERN
0.1 1.0 10 100 1,000 10,000
Pore diameter, nm
Kn = 0.001
Kn = 0.01
Kn = 0.1
Kn = 10
Kn + 10 with
Transitiondiffusion Fickdiffusion Slippagefow
FIG. 6 CO2 TRANSPORT IN CORES
Temperature = 45° C.
Pressure = 5 MPa
1 10 100 1,000 10,000
Pore diameter, nm
FIG. 7 OIL-RECOVERY MECHANISMS
CO2 + oil
MICP technology also was used to analyze gas flow through different pore
sizes. Core-flooding experiments observed the response of pore characteristics to CO2 injection and oil recovery.
Fig. 1 depicts the core flooding experiment. Samples were dried at 80°
C. for 24 hr and placed in a core holder for vacuum treatment. Cores were
saturated with 3.5% sodium chloride,
stored for 10 hr and then flooded with
1 ml/min of decane until no brine exited the outlet, establishing water saturation as the difference between entered brine and displaced brine.
After soaking, workers injected CO2
at 0.15 ml/min and monitored oil production.
Workers closed the oil outlet once
CO2 broke through, maintained 5 MPa
for 12 hr, and then slowly reopened
the outlet for more CO2 injection until
The experiment indicated pores of
10 nanometer (nm) to 100 µm. Fig. 2
shows that all four limestone samples
demonstrated typical bimodal-pore
Fig. 3 shows cumulative pore volume for four samples having different
permeability. Cumulative pore volume
was divided using a critical 1 µm pore
size. Higher-permeability samples had
larger cumulative pore volume above
the critical pore size as did high-po-rosity samples.
Permeability was controlled primarily by macroporosity (pore sizes
above 1 µm). Pore sizes less than 1
µm contributed little to permeability.
Greater explanation of microporosity’s
quantitative effect on permeability in
carbonates lies outside the scope of
this article, but can be found in previous research. 6-8
Each sample, especially the Wisconsin sample, was low permeability.
Researchers used the unsteady-state
method to measure permeability,
monitoring CO2 pressure in the inlet
A numerical model resolved the
partial differential equation of unsteady-state flow to determine the sam-