Observing diffusion between oil and CO₂ when CO₂ is stored in oil reservoirs

What is it about?

Carbon dioxide (CO₂) is a greenhouse gas, and its accumulation in the atmosphere contributes to global warming. Thus, reducing its levels in the atmosphere is crucial for the environment. Methods that capture CO₂ from the atmosphere and store it underground can help. Injecting the CO₂ into nearly empty oil reservoirs has an added economic benefit too, because this will help extract any remaining oil. But to do this, it is important to understand how CO₂ and oil diffuse into each other at the molecular level. To find the answer, this study developed an experimental setup. CO₂ was passed through a spongy material filled with oil and the pressure in the system was checked as CO₂ and oil diffused into each other. The diffusion coefficients (which help understand CO₂ diffusion to the oil phase) were then estimated considering the capillary action and absorption effects introduced by the pores.

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Photo by Matthias Heyde on Unsplash

Photo by Matthias Heyde on Unsplash

Why is it important?

Oil reservoirs are great places to store CO₂ to reduce its levels in the atmosphere. Right now, the use of CO₂ for oil recovery is a proven enhanced oil recovery technique, with oil reservoirs capable of storing about 320 million tons of CO₂. Given its potential for carbon capture and storage, it is important that the distribution of oil and CO₂ in the reservoir is studied and factors that could influence it are understood. KEY TAKEAWAY: The extent to which CO₂ and oil diffuse with each other was found to depend on the reservoir conditions and the properties of the oil and CO₂. Diffusion was found to increase with a decrease in reservoir pressure, oil viscosity, and heavy hydrocarbon levels in the oil. The effect of absorption due to the pores in the media was also found to significantly affect the distribution of oil and CO₂. These insights can lead to a better method of injecting CO₂ for oil recovery and reducing its levels in the atmosphere.