Audience-Pleasing Physical Models to Support CO2 Outreach

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Demo 5 — Reservoir in a Jar [See supplies and materials]

We tell people that one of the options to releasing CO2 into the atmosphere is to capture it and store or sequester it underground. What exactly does that mean? Some participants imagine a big cave, which seems like it might collapse or blow out. This model lets them see how CO2 could be stored underground in pores in the rock and how it is trapped by reservoir seals and phase trapping.

Set-up: Check the clear glass jar to make sure that the lid can be fastened water-tight. Just like real CO2 storage, we want to make sure that our demo doesn’t leak. Fill the jar with clear glass marbles, but don’t overfill. Several sizes of marbles make the model more interesting. Add 2 to 3 oz of colored lamp oil. Fill the jar with tap water, and put the lid on tightly (figure 8).

Demo: The jar shows you what you would see if you had a microscopic view of a CO2 storage site underground. The marbles are sand grains, and the water is salt water that fills the spaces. Have participants tip the jar from vertical to near horizontal and watch the “CO2” move through the holes in between the marbles. CO2 floats on top of water, so it tries to move upward. It is held underground by seals on the injection zone, just like this “CO2” is held in by the sides and walls of the jar. The small pores are the “microcaves” that would store the CO2 underground. CO2 is also prevented from escape because it is trapped as small bubbles snap off from the main body. This is a persistent characteristic of two-phase behavior, and it may be important in ensuring that CO2 stays underground. Try jostling the bottle. It is pretty hard to get those phase-trapped bubbles to move!

Figure 8. Using marbles in a jar to help visualize two-phase flow underground.