What is Geological Sequestration?

Why is Geological Sequestration Important?

Geological sequestration is important because it provides a way to reduce CO₂ emissions from hard-to-decarbonize industries, such as cement and steel production, which continue to rely on fossil fuels. By storing CO₂ underground, it helps address emissions that can’t be easily reduced through renewable energy or efficiency alone, making it an essential part of climate action strategies.

How Does Geological Sequestration Work?

Geological sequestration involves several key steps:

1. Capture: CO₂ is captured from emission sources like power plants or industrial facilities.
2. Compression and Transport: The CO₂ is compressed and transported, usually by pipeline, to a storage site.
3. Injection: CO₂ is injected into deep underground rock formations where it is trapped by both the physical structure of the rock and various natural trapping mechanisms.

What Types of Geological Formations are Used for CO₂ Storage?

Common formations used for CO₂ storage include:

• Saline Aquifers: Deep underground formations filled with salty water, ideal for CO₂ storage due to their large volume and isolation from potable water sources.
• Depleted Oil and Gas Reservoirs: Former oil and gas fields have proven geological integrity and can store CO₂ in the same way they held hydrocarbons.
• Unmineable Coal Seams: CO₂ can be stored in coal seams that are too deep or inaccessible for mining, where it binds with coal surfaces.

What Are the Main Trapping Mechanisms in Geological Sequestration?

Geological sequestration relies on several trapping mechanisms to secure CO₂ underground:

1. Structural Trapping: CO₂ is trapped beneath a caprock layer that acts as a seal, preventing it from escaping.
2. Residual Trapping: CO₂ becomes trapped in tiny rock pores and can’t move, even if there’s a pathway.
3. Dissolution Trapping: CO₂ dissolves into the saline water within the rock, making it stable and less likely to migrate.
4. Mineral Trapping: Over time, CO₂ reacts with minerals in the rock to form stable, solid compounds, permanently locking it in place.

How Long Can CO₂ Stay Underground?

CO₂ stored through geological sequestration can remain underground for thousands to millions of years. The different trapping mechanisms (structural, dissolution, mineralization) gradually increase in security over time, with mineral trapping often permanently locking CO₂ into solid minerals.

Is Geological Sequestration Safe?

Yes, geological sequestration is considered safe when proper site selection, monitoring, and management practices are in place. Storage sites are chosen for their stable geological features and capped by impermeable rock layers that prevent CO₂ from escaping to the surface. Additionally, ongoing monitoring ensures any issues are detected and addressed promptly.

How is Geological Sequestration Monitored?

To ensure CO₂ remains securely stored, several monitoring techniques are used:

• Seismic Surveys: Imaging technology to track CO₂ movement and detect changes in the formation.
• Pressure and Temperature Sensors: Used to monitor conditions within the storage site.
• Geochemical Sampling: Analyzing water and rock samples to confirm CO₂ is not leaking and that it remains within the formation.
• Surface Monitoring: Sensors above ground detect any unexpected CO₂ movement or leaks.

What Are the Benefits of Geological Sequestration?

Geological sequestration offers numerous benefits:

• Reduces Atmospheric CO₂: By isolating CO₂ underground, it directly lowers greenhouse gas levels in the atmosphere.
• Supports Industrial Decarbonization: Provides a solution for industries that can’t easily reduce emissions through renewable energy.
• Utilizes Existing Infrastructure: Depleted oil and gas fields with established pipelines can sometimes be repurposed for CO₂ storage.
• Long-Term Stability: Natural trapping mechanisms ensure CO₂ remains safely stored over long timescales.

What Are the Challenges of Geological Sequestration?

While geological sequestration has great potential, it also faces several challenges:

• High Costs: Capturing, transporting, and storing CO₂ is expensive, though costs are decreasing as technology advances.
• Energy Use: Compressing and transporting CO₂ requires energy, which can offset some emissions savings.
• Public Perception and Regulatory Hurdles: Concerns about safety and environmental impact can lead to regulatory and public acceptance issues.
• Leakage Risks: Although low, there is a possibility of CO₂ leakage, requiring thorough monitoring and risk management.

What Role Does Geological Sequestration Play in Carbon Capture and Storage (CCS)?

Geological sequestration is a key component of CCS, providing the storage phase after CO₂ is captured from emissions sources. While capture and transportation reduce the amount of CO₂ entering the atmosphere, geological sequestration completes the process by providing a long-term storage solution.

How Much CO₂ Can Geological Sequestration Store?

Geological formations, particularly saline aquifers and depleted reservoirs, have vast storage capacities. Estimates suggest that these formations could theoretically store hundreds of gigatons of CO₂ globally, which is enough to accommodate a significant portion of industrial emissions for decades.

How Does Geological Sequestration Compare to Other CO₂ Storage Methods?

Geological sequestration is one of the most established and scalable CO₂ storage methods. Unlike surface storage or biological sequestration, geological storage is designed for long-term containment. It can store larger volumes of CO₂ than methods like soil carbon sequestration or afforestation, making it essential for managing industrial-scale emissions.

What Is the Difference Between Geological Sequestration and Carbon Capture?

Geological sequestration is the storage phase, where CO₂ is injected and trapped in underground formations. Carbon capture, on the other hand, refers to the process of capturing CO₂ emissions from industrial sources, such as power plants or factories, before it is transported to a storage site. Both steps are essential in CCS.

What Happens if CO₂ Escapes from a Geological Storage Site?

While the risk is low, if CO₂ were to escape, it would be detected through monitoring systems in place. Immediate actions would include adjusting pressures or sealing pathways to stop the release. Advanced site selection and risk assessments help minimize leakage risks, and most geological sequestration sites have natural caprock formations to contain the CO₂.

Is Geological Sequestration Compatible with Direct Air Capture (DAC)?

Yes, geological sequestration can be paired with Direct Air Capture (DAC), which captures CO₂ directly from the air. After CO₂ is removed from the atmosphere using DAC technology, it can be compressed and stored underground through geological sequestration, providing a way to reduce existing atmospheric CO₂ levels.

How Does Geological Sequestration Help with Climate Goals?

Geological sequestration helps meet climate goals by capturing and storing emissions that would otherwise contribute to global warming. It is especially valuable for industries that are difficult to decarbonize and complements renewable energy by addressing emissions that can’t be easily eliminated.

Is Geological Sequestration Scalable?

Yes, geological sequestration is scalable, but it requires significant investment in infrastructure and regulatory support. With the vast storage potential of saline aquifers and depleted oil fields, geological sequestration can accommodate large volumes of CO₂, making it feasible for managing emissions at an industrial scale.

Are There Any Environmental Concerns with Geological Sequestration?

Some environmental concerns exist, including potential risks of groundwater contamination or induced seismic activity. However, with thorough site assessments, careful monitoring, and regulatory oversight, these risks are minimized. Geological sequestration projects are designed to operate safely and mitigate any potential impacts.