Fluids and Rocks - Introduction to Carbon Capture and Sequestration - page 432

Brine imbibition P c curve

Ideal P c curve

P c

CO 2 invasion P c curve

S w

0 S g,r

1

Figure 9.7.6 Ideal capillary pressure curve
Illustration of the hysteresis of the capillary pressure curve of a rock sample. The solid
line shows a schematic view of the ideal P c curve that would be calculated from the
distribution of capillary entry pressures of all pores in the porous medium. The dashed
lines illustrate how the ideal P c curve is shifted to higher or lower P c values during CO 2
invasion and brine imbibition, respectively. Shifting the curve upward does not funda-
mentally change the character of the multiphase fl ow process; shifting the curve down-
ward gives rise to a new phenomenon: residual CO 2 trapping.

structured distribution of the invading fl uid suggests that the invasion
process is very complicated. Upon closer inspection, however, the
authors of this study discovered that the CO 2 distribution is almost identi-
cal to the distribution that would be predicted from the Young-Laplace
equation: the larger pores are fi lled with CO 2 while the smaller pores
remain fi lled with water. The CO 2 distribution looks complicated because
of the heterogeneous distribution of pore sizes in the sample (for exam-
ple, the region highlighted on the left side of Figure 9.7.7 has somewhat
smaller pores than the rest of the sample, therefore it is almost entirely
bypassed by the invading CO 2 ) but the basic processes that determine
the CO 2 invasion pattern are those that are embodied in the ideal P c
curve in Figure 9.7.6 .
The second fi gure ( Figure 9.7.8 ) shows a photograph of brine and
residually trapped CO 2 bubbles in a glass micromodel. The experimental