How Clay Minerals Help Trap Carbon Dioxide During Oil Recovery

Jim Crocker
7th September, 2025

How Clay Minerals Help Trap Carbon Dioxide During Oil Recovery

Percentage of sediment mass at different injection pressures.

Image adapted from: Zhang et al. / CC BY (Source)

Key Findings

  • This study, conducted in strongly water-sensitive reservoirs, investigates how clay minerals affect oil recovery and carbon dioxide (CO2) storage
  • Clay minerals promote asphaltene deposition during CO2 injection, increasing it by 37% in clay-containing crude oil compared to clay-free samples
  • Despite some reduction in reservoir permeability due to asphaltene buildup, CO2 sequestration rates increase with higher clay content, ranging from 43.15% to 48.21% as clay content rises
Extracting oil from the ground isn’t always simple. Often, oil remains trapped within porous rock formations, and simply drilling isn’t enough to get it out. Enhanced Oil Recovery (EOR) techniques are used to improve the amount of oil we can extract, and one promising method is injecting carbon dioxide (CO2) into the reservoir. This has the added benefit of potentially trapping the CO2 underground, acting as a form of carbon sequestration – removing it from the atmosphere. However, a major challenge with CO2 injection is the tendency for asphaltenes to precipitate out of the oil and deposit within the rock, blocking pores and reducing the flow of oil[2][3]. This is especially problematic in reservoirs containing a lot of clay. A recent study by researchers at Northeast Petroleum University, Daqing Yongzhu Petroleum Technology, and Dawood University of Engineering & Technology[1] investigated how clay minerals influence this process, aiming to optimize both oil recovery and CO2 storage. The core of the problem lies in the complex interactions between the oil, the CO2, and the clay present in the reservoir rock. Clay minerals are tiny particles that can swell when exposed to water, further restricting the flow pathways for oil. The study began by examining how clay interacts with oil in the presence of CO2. The results showed a significant increase in asphaltene deposition – a 37% rise in clay-containing crude oil compared to clay-free samples. This suggests that clay plays an active role in promoting the precipitation of these troublesome compounds. To understand how this happens, the researchers measured several key properties. Interfacial tension (IFT) – the resistance between the oil and CO2 – decreased as clay content increased. Lower IFT is generally beneficial for oil recovery, as it allows the CO2 to spread more easily through the oil. Simultaneously, the viscosity of the oil decreased significantly (up to 43.58% reduction) with CO2 injection exceeding 30 mol%. This also aids oil flow. However, the increased asphaltene deposition counteracts these benefits. The team used nuclear magnetic resonance (NMR) to visualize what was happening at a microscopic level. NMR works by detecting the magnetic properties of atoms within a sample, providing information about pore size and fluid distribution. This revealed that the clay-asphaltene aggregates preferentially blocked the larger pores within the rock. This might seem negative, but it also has a surprising consequence: it forces the CO2 into the smaller pores. This is significant because smaller pores are less likely to be swept by the oil during production, making them ideal locations for long-term CO2 storage. To confirm these findings at a larger scale, the researchers conducted long-core water flooding tests – essentially simulating the oil recovery process in a laboratory setting. These tests demonstrated that reservoirs with higher clay content exhibited a greater CO2 sequestration rate, increasing from 43.15% to 48.21% as clay content rose from 8.35% to 29.92%. While the asphaltene deposition did cause some reduction in permeability (the ability of fluids to flow through the rock), the overall effect was a balance between oil recovery and secure CO2 storage. These results build upon previous research into asphaltene precipitation during gas injection[2][3][4]. Earlier studies highlighted the challenges of asphaltene deposition when using CO2 and flue gas for EOR, noting that CO2 injection, while more effective at displacing oil, also caused greater formation damage[2]. Another study quantified asphaltene precipitation with multiple methane contacts, revealing that the loss of asphaltene stability during the injection process is crucial[4]. The current study expands on this by identifying the specific role of clay minerals in accelerating this process and directing the CO2 into smaller pores. Furthermore, the findings align with a review emphasizing the importance of kinetics in understanding asphaltene behavior, suggesting that short-term evaluations may not fully capture the complexities of asphaltene precipitation in real-world conditions[3]. The research suggests that the mechanism of permeability reduction caused by asphaltene precipitation is dependent on pore throat size and the size of the asphaltene particles[4]. In this instance, the preferential blocking of larger pores by clay-asphaltene aggregates acts as a form of “conformance control,” optimizing the flow of CO2 and enhancing storage potential. The study demonstrates that, while asphaltene deposition is a concern, it can be strategically managed to achieve both improved oil recovery and effective geological sequestration, particularly in clay-rich reservoirs.

AgricultureEnvironmentSustainability

References

Main Study

1) Mechanisms of clay mineral-induced targeted deposition and synergistic CO2 sequestration potential in the CCUS-EOR process

Published 5th September, 2025

https://doi.org/10.1371/journal.pone.0331674

Related Studies

2) Experimental study of asphaltene deposition during CO2 and flue gas injection EOR methods employing a long core.

https://doi.org/10.1038/s41598-024-54395-0

3) Review on asphaltene precipitation and deposition kinetics and CO2 interactions.

https://doi.org/10.1016/j.cis.2025.103488

4) Quantification of Methane-Induced Asphaltene Precipitation in a Multiple Contact Process.

https://doi.org/10.1021/acsomega.2c05480


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