The vast potential for permanently storing carbon dioxide underground by using it for enhanced oil recovery can only be realized if produced or captured CO2 can be economically transported long distances via pipeline. And the only way that can happen is if the CO2 is compressed into a “supercritical” or “dense-phase” fluid — a state that is somewhat compressible like a gas but flows and can be pumped like a liquid. When CO2 is in a supercritical state, much more of it can economically flow through a pipeline to the producing field. And when it gets there, the dense-phase CO2 can be injected into an oil production zone, where it has the unique ability to flow through permeable rock formations, bond with and “swell” trapped oil molecules, and free the oil to move to the production well, then up to the surface. Given that CO2-based EOR is destined to become a much more significant activity in the energy industry, it’s time for a fun-filled review of the thermodynamics of fluids as it relates to the transportation of CO2 and its use in the production of crude oil. (Wait! Don’t leave! This will be easy to follow! We promise!) Today, we continue our series on the rapidly evolving CO2 market and why it matters to crude oil producers.
As we said in Part 1 of this blog series, CO2 sequestration is the permanent storage of CO2 deep below ground in rock formations, oil and gas reservoirs, coal seams, etc. If the CO2 is captured and stored, and that’s all, the process is called CCS (Carbon Capture and Storage). On the other hand, if the CO2 is used for some other process before it’s stored, it is called CCUS (Carbon Capture, Use, and Storage). EOR is a form of CCUS, and a very economic one at that. In EOR, CO2 is pumped into the production zone of an otherwise depleted oil field, then mixes with and frees the oil that has been left behind. Some of the CO2 used in this process stays underground, permanently trapped in the reservoir. The rest of the CO2 comes out of the ground mixed with the oil, then is separated and recycled back into the field — a process that goes on until all the original CO2 used is trapped beneath the surface.
We also pointed out the paradox that while the CO2 stored underground in the U.S. through EOR accounts for most of the CO2 sequestered globally, much of the CO2 used for EOR is tapped from natural CO2 reservoirs and piped to oil fields. In other words, it’s taken out of the ground to be put back in the ground, with no net impact on U.S. CO2 emissions. Switch to man-made or “anthropogenic” CO2 (a.k.a. A-CO2) as the source, though, and expanded use of EOR could have a game-changing impact. In Part 2, we did deep dives both into how the CO2/EOR process works, and the economics driving the use of the process. In Part 3, we shifted our focus to CO2 sourcing and the CO2 pipeline networks that have been developed to transport both produced and captured CO2 to oil fields for EOR, as well as to other sequestration sites.
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