Fluids and Rocks - Introduction to Carbon Capture and Sequestration - page 434

Figure 9.7.8 Residual trapping in a glass micromodel
Photograph showing residually trapped CO 2 bubbles in a glass micromodel (2 x 1 cm)
at 8.5 MPa and 45°C. The pore space in the micromodel was initially fi lled with a 5 M
NaCl brine; CO 2 was then injected at constant fl ow rate until CO 2 saturation reached a
stable value ( S g,i = 0.91); fi nally, brine was injected at a constant fl ow rate until CO 2 satu-
ration reached a new stable value ( S g,r = 0.19). Figure courtesy of Jiamin Wan (Lawrence
Berkeley National Laboratory).
the Young-Laplace equation would predict that each pore should contain
a trapped CO 2 bubble. Clearly this is not the case, so the fl uid dynamics
of the imbibition process must infl uence S g,r (see also Question 9.7.2 ).
We note in passing that CO 2 residual trapping does not occur only
during brine imbibition: CO 2 exsolution from brine in porous rocks also
results in a distribution of disconnected CO 2 bubbles ( Movie 9.7.1 ). One
implication of this is that if a CO 2 -saturated brine becomes depressurized
(for example, during leakage of CO 2 -saturated brine), the exsolved CO 2
bubbles could have a very low mobility because of residual CO 2
trapping.