Geologic carbon sequestration is the process of storing carbon dioxide (CO2) in underground geologic formations. CO2 can be stored in oil reservoirs, gas reservoirs, unmineable coal seams, saline formations, and organic-rich shale formations. Increasing investments have been made to develop technology in the field of carbon sequestration and combat the threat of climate change. As global warming accelerates and society continues to emit greenhouse gases, the idea of investing in artificial carbon sequestration techniques is gaining traction. Geologic sequestration is thought to have the most immediate application potential. In this article, we will discuss Geologic Sequestration which will be helpful for UPSC exam preparation.

What is Geologic Sequestration?

• Geologic carbon sequestration is the process of storing carbon dioxide (CO2) in underground geologic formations.
• CO2 is typically pressurized until it becomes a liquid before being injected into porous rock formations in geologic basins.
• Because it is typically used later in the life of a producing oil well, this method of carbon storage is sometimes included in enhanced oil recovery, also known as tertiary recovery.
• In enhanced oil recovery, liquid CO2 is injected into the oil-bearing formation to reduce the viscosity of the oil and allow it to flow more easily to the oil well.
• Carbon dioxide is typically captured and injected into porous rocks for long-term storage from an industrial source, such as steel or cement production, or an energy-related source, such as a power plant or natural gas processing facility.

Process of Geologic Carbon Sequestration

Sequestration Strategy

• The first stage of geologic carbon sequestration is the Sequestration Strategy.
• This stage's primary goal is to determine the basis for CO2 removal and how it fits into the organization's carbon action plan.
• Firstly, CO2 removal enables Carbon Neutral Production (CNP) operation. CNP aids in the development of carbon-neutral fuels.
• Second, it could be a focused sequestration operation.
• Finally, the procedure entails permanently storing all of a company's CO2 emissions underground, without any associated production.
• As a result, as the first step, you must determine how sequestration will fit into a specific organization's carbon dioxide reduction strategy.

Reservoir Modeling and Simulations

• Reservoir Modeling and Simulations is a reservoir engineering process that works in reverse. Engineers can develop a plan for how the reservoir will function at this stage.
• Engineers then take a backwards approach to see what happens when carbon is liquified with a compressor and then injected back into the rock formation.
• Understanding the effects of injecting carbon dioxide deep beneath the earth's surface necessitates specialised knowledge.
• The process necessitates a broad and multidisciplinary approach that includes seismic analysis, zone analysis, permeability evaluations, volume calculations, Equation of State (EOS) fluid property analyses, stratification, depth, and much more.

Well Engineering

• Once the carbon dioxide has been isolated, the engineers must create a road map to the desired depth and location.
• The engineers will then create a well that will transport carbon from the surface to the target well.
• Several control measures are put in place to ensure that no carbon escapes during this process.
• The safeguards include delivering a significant well depth and constructing multiple casing layers on the well as well as natural geologic barriers.

Secure Geologic Storage

• The supercritical fluid carbon dioxide is directed and injected into the reservoir once the engineered wells are completed.
• Most target reserve zones are well-structured and have a track record of trapping buoyant fluids and securely containing them for millions of years.
• As a result, reservoirs are frequently depleted of oil and gas, or saline formations. CO2 is contained within the subsurface rock in three states:
  • Solution Trapping: CO2 dissolves into hydrocarbons or saline water in the reservoir, where it becomes a part of the reservoir fluid in the caprock.
  • Residual Trapping: The supercritical fluid, carbon dioxide, is trapped in the porous space of the subsurface rock by the same forces that hold water in a sponge.
  • Mineral Trapping: The CO2 solution reacts with the minerals in the rocks to form new minerals. The method ensures that CO2 is permanently trapped in the subsurface.

Geologic Sequestration Trapping Mechanisms

Hydrodynamic Trapping​

• CO2 is trapped as a supercritical fluid or gas under a low-permeability caprock in a process known as hydrodynamic trapping.
• Because carbon dioxide is less dense than formation fluid, it will rise buoyantly until it comes into contact with a caprock with a capillary entry pressure greater than the buoyancy or hydrodynamic force.
• CO2 will build up in a structural or stratigraphic feature with both vertical and lateral seals.
• Trapping by such a seal is known as structural, stratigraphic, or hydrodynamic trapping.
• This mechanism is critical because it prevents CO2 leakage through the caprock during the time it takes for other trapping mechanisms to take effect, which is required for any storage site.

Solubility Trapping

• Solubility trapping refers to the dissolution of CO2 in formation fluid.
• After injection, CO2 would migrate upwards to the interface between reservoir and caprock, then spread laterally under caprock as a separate phase.
• When CO2 comes into contact with the ambient formation brine and hydrocarbon, mass transfer occurs, with CO2 dissolving into the brine until an equilibrium state is reached.
• The solubility of CO2 in water is affected by the salinity, pressure, and temperature of the formation water.
• CO2 dissolves into water via molecular diffusion at the interface of the free gas phase and the formation water.
• Water in contact with CO2 will become saturated with CO2 and a CO2 concentration gradient will form spatially.
• Because the molecular diffusion coefficient is so small, this process is extremely slow. CO2 will take thousands of years to dissolve completely in brine.

Mineral Carbonation

• Carbon dioxide has the ability to react with minerals, fluids, and organic matter in a geologic formation to form stable compounds/minerals, primarily calcium, iron, and magnesium carbonates.
• Mineral trapping is the incorporation of CO2 into a stable mineral phase during the formation process via reactions with mineral and organic matter.
• The injected CO2 will dissolve into the local formation water over time, triggering a number of geochemical reactions.
• Some of these reactions may be beneficial, assisting in the chemical containment or "trapping" of CO2 as dissolved species and the formation of new carbonate minerals; others may be detrimental, assisting in CO2 migration.
• It is critical to comprehend the cumulative effect of these competing processes.
• These processes, however, will be influenced by the structure, mineralogy, and hydrogeology of the specific lithologies involved.

Conclusion

Carbon sequestration stores carbon dioxide in order to keep it from entering the Earth's atmosphere. The goal is to stabilise carbon in both solid and dissolved forms so that it does not warm the atmosphere. Carbon dioxide storage is a technology that is here to stay, with the benefit of allowing the continued use of fossil fuels while still protecting our environment from the dangers of global warming, and it must therefore be embraced by all.

FAQs

MCQs

1. Which of the following is a primary method used for geologic sequestration?

A) Solar energy capture
B) Deep saline aquifers
C) Wind turbine installations
D) Bioenergy with carbon capture and storage (BECCS)

2. What is the main environmental risk associated with geologic sequestration?

A) CO2 leakage
B) Increased energy consumption
C) Soil erosion
D) Airborne particulate matter

3. What is the role of unmineable coal seams in geologic sequestration?

A) They are used for storing methane
B) They release CO2 into the atmosphere
C) They absorb CO2 and release methane for energy production
D) They prevent CO2 leakage

4. What is a major benefit of using geologic sequestration to mitigate climate change?

A) Reduction in carbon emissions
B) Increased fossil fuel dependence
C) Reduced need for renewable energy
D) Increased coal mining

5. How can government policies support geologic sequestration technologies?

A) By banning all fossil fuel usage
B) By providing research funding and tax incentives
C) By imposing stricter emission limits only
D) By focusing solely on renewable energy sources

GS Mains Questions and Model Answers

Q1: Analyze the potential of geologic sequestration in mitigating global climate change.

Answer: Geologic sequestration has a significant potential for mitigating climate change by capturing and storing carbon dioxide (CO2) deep underground, preventing its release into the atmosphere. As part of carbon capture and storage (CCS) technologies, it could become an essential tool for reducing emissions from industries that are difficult to decarbonize, such as cement and steel production. Despite challenges like CO2 leakage and induced seismicity, the technology has been proven in pilot projects and is seen as a bridge technology that allows for the continued use of fossil fuels while reducing their impact on the climate. For geologic sequestration to scale globally, it will require significant investment in infrastructure, regulatory frameworks, and long-term monitoring systems to ensure safety and efficacy.

Q2: Discuss the environmental and social challenges of implementing geologic sequestration technologies.

Answer: The implementation of geologic sequestration faces several environmental and social challenges. Environmentally, the risks of CO2 leakage and induced seismicity (small earthquakes caused by CO2 injection) are of major concern. These risks could undermine the effectiveness of sequestration and even lead to negative environmental consequences. Socially, there are concerns regarding the proximity of sequestration sites to local communities, especially regarding the safety of water supplies and public health. Public acceptance is often a barrier, as communities may resist having CO2 storage sites near them. Additionally, there is the challenge of ensuring that sequestration sites are maintained and monitored over long periods of time, potentially hundreds of years. Balancing environmental safety with social acceptance is key to the widespread deployment of this technology.

Q3: Evaluate the role of geologic sequestration in the transition towards a sustainable low-carbon energy future.

Answer: Geologic sequestration plays a crucial role in the transition towards a low-carbon energy future by providing a solution for reducing CO2 emissions from fossil fuel-based power plants and industrial processes. While renewable energy sources such as wind and solar are essential for long-term sustainability, geologic sequestration allows for the continued use of existing infrastructure and energy sources without exacerbating climate change. In regions where renewables cannot yet meet all energy demands, sequestration technologies can help decarbonize sectors like cement production, steel manufacturing, and oil refining. However, for geologic sequestration to be part of a sustainable energy future, it must be paired with strong climate policies, technological innovation, and continued investment in renewable energy alternatives.

Previous Year Questions on Geologic Sequestration and Climate Change

1. UPSC CSE Prelims 2021:

Question: Which of the following is the primary objective of geologic sequestration?

A) To increase fossil fuel production
B) To capture and store CO2 emissions
C) To promote renewable energy
D) To enhance crop production

Answer: (B)

Explanation: The primary objective of geologic sequestration is to capture and store CO2 emissions in deep underground rock formations to prevent them from entering the atmosphere and contributing to climate change.

2. UPSC CSE Mains 2020 (GS Paper 3):

Question: Evaluate the role of geologic sequestration in the context of global climate mitigation strategies.

Answer: Geologic sequestration is a vital strategy in global climate mitigation efforts as it offers a way to reduce CO2 emissions from sectors that are difficult to decarbonize, such as energy and industrial sectors. It complements renewable energy sources and helps to manage emissions while transitioning to a low-carbon economy. However, to ensure its effectiveness, it requires stringent monitoring, advanced technology, and regulatory frameworks to mitigate risks like leakage and environmental degradation.