Sedimentary Rocks: Key to Hydrocarbons & Clean Energies

1. Introduction: The Deep Beat of the Earth

Some natural settings inspire contemplation and humility, feelings that become profound and almost mystical, tinged with cultural heritage and the mysteries of humanity. Sedimentary rocks, with secrets trapped in every stratum, constitute one such scenario. They simultaneously hold the fossil remains that fueled industrial development for over a century and the technological promises of a zero-emission future.

This text explores the connection between hydrocarbon geology and the potential for storing clean energy—particularly CO₂ and, more recently, hydrogen—in the porous depths of sedimentary formations. To ensure rigor, we will analyze recent research by geologists, engineers, and scientists, providing readers with concrete data and reasons to reflect and act.

2. A Review of the Relevance of Sedimentary Rocks

2.1 The Geological Foundation of Fossil Fuels

Sedimentary rocks are the product of millions of years of accumulated mineral fragments, organic matter, salts, and other materials deposited in marine or continental basins. The first act of this geological history can be traced back to ancient times when microscopic marine organisms (phytoplankton, zooplankton, and bacteria) and terrestrial plants accumulated in low-oxygen environments. Over time, this organic matter became trapped beneath increasingly thick sediments. Rising pressures and temperatures slowly transformed this material into hydrocarbons: oil and natural gas.

Since the Industrial Revolution, humanity has exploited these sedimentary rocks as the primary energy source. According to the U.S. Energy Information Administration (EIA), more than 80% of the primary energy used worldwide in the 20th century came from fossil fuels trapped in sedimentary formations. Even today, in 2025, oil and natural gas still account for about 55-60% of the global energy mix, though the transition to renewables accelerates yearly.

2.2 The Legacy of Petroleum Geology

The study of oil and gas reservoirs has, over decades, generated a sophisticated understanding of the structure and behavior of rock reservoirs. Companies and academic institutions worldwide have invested significant resources in exploring and mapping sedimentary basins, modeling rock porosity and permeability, developing drilling and extraction techniques, and perfecting secondary and tertiary recovery methods. This knowledge, essential to the hydrocarbon industry, provides an invaluable foundation when considering converting these same geological formations into storage sites for CO₂ or hydrogen.

3. From Fossil Carbon to Captured Carbon: The CO₂ Option

3.1 The Climate Emergency

The fossil fuels provided by sedimentary rocks for so long are paradoxically responsible for most carbon dioxide (CO₂) emissions that are altering the Earth's climate. The Intergovernmental Panel on Climate Change (IPCC), in its latest cycle of reports (AR6, published between 2021 and 2022), underscores the urgent need to drastically reduce CO₂ emissions to limit global warming to 1.5°C or, at worst, 2°C above pre-industrial levels.

While the transition to renewable energies (solar, wind, geothermal, etc.) is gaining momentum, fossil fuel use persists in many emerging economies, complicating a 100% immediate replacement. In this scenario, carbon capture and storage (CCS) becomes relevant as a bridge—perhaps not definitive but necessary—toward a future where CO₂ emissions are significantly reduced.

3.2 The Role of Sedimentary Rocks in CO₂ Capture and Storage

CCS involves three main steps:

1. Capturing CO₂ from industrial plants or thermal power stations.

2. Transporting CO₂ through pipelines or specialized ships.

3. Injecting and storing CO₂ in stable geological formations.

For this last step, sedimentary rocks that previously hosted oil or natural gas are ideal candidates. This is due to their porosity and permeability and the existence of geological traps and cap rocks capable of preventing surface leaks.

Some figures illustrate its potential:

• A 2022 report by the International Energy Agency (IEA) estimates that the global geological storage capacity for CO₂ in sedimentary formations ranges between 8,000 and 10,000 gigatons (Gt). To put this in context, global annual CO₂ emissions are around 36 Gt, as of 2023.

• In North America alone, the North American Carbon Storage Atlas (NACSA) suggests the capacity to inject several hundred gigatons of CO₂ into deep sedimentary basins.

Decades of experience in drilling, reservoir characterization, and monitoring from the oil industry translate into knowledge that can be applied to designing and managing CO₂ injection projects. Indeed, pioneering projects like Sleipner in the North Sea (operated by Equinor) and Weyburn in Canada have demonstrated the technical and economic feasibility of injecting CO₂ into deep sedimentary formations for extended periods, with negligible leakage.

4. Hydrogen: The Fuel of the Future and Its Geology Connection

4.1 The Hydrogen Revolution

Hydrogen—particularly the so-called “green hydrogen,” produced from renewable sources and water electrolysis—has become a major focus for decarbonizing industrial sectors and heavy transportation that are difficult to electrify (such as the steel or maritime industries). The International Renewable Energy Agency (IRENA) estimates that hydrogen's share in the global energy mix could reach 12% by 2050 if investments and supportive policies continue.

However, hydrogen has a significant challenge: storage. At ambient temperature and pressure, it is a very light and voluminous gas, making its transport expensive and its safe handling in large quantities difficult. Therefore, alternatives such as cryogenic tanks and chemical hydrates have been studied. However, in recent years, the possibility of injecting hydrogen into deep geological reservoirs, leveraging the same infrastructure and knowledge of the hydrocarbon industry, has gained great interest.

4.2 Why Sedimentary Formations Can Serve as Hydrogen Storage

When sedimentary rock has sufficient porosity—spaces between mineral grains—and a geological seal to prevent leaks, it becomes a natural reservoir. Experts indicate that many basins historically used for natural gas storage could be repurposed for hydrogen storage. Some advantages and challenges include:

• Advantages:

  • High storage capacity compared to surface deposits or pressurized tanks.

  • Potential to reuse petroleum or gas infrastructure (pipelines, wells, compression stations).

  • Accumulated experience of geologists and engineers in characterizing and supervising reservoir integrity.

• Challenges:

  • Reactivity: Hydrogen can react with certain minerals and/or microorganisms present in the formation, causing porosity changes or the appearance of H₂S (hydrogen sulfide).

  • Leaks: Hydrogen is a very small molecule that can migrate through seals less permeable to denser gases, necessitating detailed studies of cap rock integrity.

  • Cost: Even with existing infrastructure, adapting wells and transport networks requires considerable investments.

Recent studies, such as those conducted by the European Underground Sun Storage consortium (2021–2023), demonstrate the feasibility of injecting mixtures of hydrogen and natural gas into porous formations about 1,000 meters deep in parts of Austria. These pilot projects suggest that leveraging sedimentary rocks for hydrogen storage could play a decisive role in developing a clean, reliable, and, above all, scalable energy market.

5. The Transition from Hydrocarbon Geology to Carbon and Hydrogen Geology

The possibility of using the same geological basins for both extracting oil and gas and storing CO₂ or hydrogen reveals an interesting irony: the rocks that have been exploited for decades to extract fossil fuels could now become allies in mitigating emissions or enabling clean fuels.

5.1 Cutting-Edge Technologies for Reservoir Characterization

Characterizing an oil and gas reservoir—or a potential storage site for CO₂ or hydrogen—relies on techniques such as:

• 3D and 4D Seismology: These techniques generate high-resolution models of the rock's internal structure and monitor changes in fluid saturation over time.

• Well Logging: Provides information on density, porosity, lithology, and fluid presence.

• Numerical Modeling: Simulates fluid behavior and interactions among rock, fluids, and barriers.

• Pilot Injection Tests: Verifies, at a field scale, the rock’s efficiency in retaining gases or liquids and the absence of significant escape routes.

Although these methodologies were originally developed for the hydrocarbon industry, they are now being applied to CCS or geological hydrogen storage projects. Similarly, well engineering techniques—such as designs and cementing methods that ensure the mechanical integrity of production pipes—are adapted for the injection and containment of non-hydrocarbon gases.

5.2 From the Oil Business to a Low-Carbon Economy

In recent years, some major oil and gas companies have shifted their discourse, investing in CO₂ capture and storage projects. At least eight “supermajors” have allocated research funds to evaluate former oil fields as potential reservoirs. For example, Equinor (formerly Statoil) in Norway has been injecting CO₂ into the Sleipner field for decades and has also shown interest in hydrogen storage.

According to the consultancy Rystad Energy, global investments in carbon capture, utilization, and storage (CCUS) projects exceeded $6 billion in 2022, with projections to double by 2025. Meanwhile, investments in hydrogen—both blue (produced from natural gas with CO₂ capture) and green (produced from renewable energy)—have grown by more than 25% annually since 2020.

For many experts, this transition aligns with the concept of a “low-carbon economy,” where net emissions tend to zero in the latter half of the 21st century. Sedimentary rocks could ironically bridge the gap between a fossil-fuel-dominated past and a future driven by clean energy.

6. Technical, Economic, and Environmental Challenges

6.1 Monitoring and Verification of Injection

A critical aspect of CO₂ or hydrogen injection into the subsurface is ensuring the gas remains stable there for decades or centuries. This requires implementing advanced monitoring, reporting, and verification (MRV) techniques, including repeated seismic measurements, tracking changes in well pressure, and sampling groundwater to detect any leaks.

For CO₂, the presence of saline water in the porous matrix promotes chemical reactions that, over time, transform part of the CO₂ into stable carbonate minerals. In Iceland, for example, the CarbFix project has successfully mineralized injected CO₂ in basalt formations—a process that, while not identical in sedimentary rocks, can occur on a smaller scale depending on the lithology and local geochemistry.

6.2 Costs and Economic Barriers

Another major challenge is financial. The International Energy Agency notes that CCS has yet to scale to the level of competitiveness needed to significantly lower global emissions, partly due to high costs and the lack of robust incentive schemes or carbon taxes. Similarly, hydrogen storage remains an emerging technology with few large-scale industrial projects.

However, the recent experience with renewable energy—solar and wind—shows that costs can plummet when public policies and innovation align. A decade ago, solar energy was significantly more expensive than conventional sources; today, in many parts of the world, it is the most economical option. A similar trajectory may be possible for CO₂ capture and hydrogen injection if regulatory frameworks are implemented and standardization advances.

6.3 Environmental and Social Considerations

Injecting gases into the subsurface requires careful management to avoid induced seismicity and potential impacts on local ecosystems. Additionally, neighboring communities must be included in the planning and decision-making processes to mitigate fears and build trust.

In an increasingly socially and environmentally conscious world, such projects cannot be imposed. Instead, they must be conceived as part of a just transition, where geological knowledge and technology serve the common good, not just corporate interests.

7. Projections and Trends: Toward a Geology of the Future

The transformation of the energy sector has raised concerns among many reservoir geologists and engineers, with discussions about a potential peak in oil demand in the 2020s or 2030s. What will happen to their field of expertise in a post-oil era? It is likely that carbon geology—focused on CO₂ mitigation—and hydrogen geology—dedicated to producing, transporting, and storing this energy vector—will consolidate as emerging and highly demanded fields.

Key trends highlighted in industry reports and recent academic publications include:

1. Development of Integrated Carbon Hubs: Several countries are advancing the creation of carbon capture and storage hubs, where multiple CO₂ emitters (cement plants, steel mills, petrochemical facilities) connect to a shared transport system and geological reservoir.

2. Improved Capture Efficiency: Research into absorbent materials and membranes for CO₂ separation, as well as oxy-combustion processes, aims to reduce costs and the energy footprint of CCS.

3. Hydrogen Storage Initiatives: Pilot projects for hydrogen injection into depleted gas fields, salt caverns, and sedimentary formations are emerging, aiming to serve as buffers or "seasonal batteries" for the energy system.

4. Renewables Synergy: Green hydrogen, produced by electrolysis with renewable energy, can be stored underground during low-demand months and extracted during peak consumption or when renewable production is insufficient. This opens a door to efficient management of wind and solar intermittency.

8. Reflections: The Cultural Substrate of Geology

One might marvel at humanity’s relentless progress, unearthing organic matter fossilized over millions of years and releasing its energy within a few decades. This tension between the need for subsistence, social awareness, and the potential double-edged sword of technology evokes fundamental questions:

• Does the geological history of the planet not teach us to respect the Earth’s deep rhythms, as opposed to the immediacy with which we often act?

• Isn’t it consistent that the same formations that brought us to the brink of climate crisis now offer a way to mitigate its effects and explore new energy pathways?

• What does it mean, culturally, to embrace geology as an integral part of the social fabric and not just as a resource to exploit?

Sedimentary rocks speak of slowness, of layer accumulation, of transformations spanning eons. This geological substrate, seemingly inert, actually records the life and death of countless organisms that, upon decomposition, gave rise to fossil fuels. Now, humanity stands at a critical juncture, needing to decide how to manage this geological heritage.

9. Concrete Cases and Examples of Innovation

To illustrate the reality of this transition, here are some projects and regions that set the pace:

1. Norway: The Northern Lights project is a pioneering initiative for CO₂ storage in the marine subsurface, part of the Longship CCS cluster. By 2030, it is expected to store up to 5 million tons of CO₂ annually from European industries.

2. United Kingdom: In the North Sea region, former oil extraction platforms could be repurposed as CO₂ injection or hydrogen storage stations. The UK government has announced commitments to reduce emissions by 78% by 2035 (compared to 1990 levels), with CCS playing a key role in achieving this.

3. Canada: Shell’s Quest project for CO₂ capture and storage has injected over 6 million tons of CO₂ into deep saline formations in Alberta. Additionally, depleted gas fields are being explored as potential hydrogen storage sites.

4. United States: The sedimentary basins of the Gulf of Mexico and the Appalachian region are considered enormous potential CO₂ storage sites. States like Texas and Louisiana are evaluating policies to attract investments in storage infrastructure.

5. Central Europe: Hydrogen storage initiatives in salt caverns, mainly in Germany and Austria, have demonstrated the feasibility of injecting and extracting hydrogen on a pilot scale. While these caverns are not classic sedimentary rocks (they are halite formations), they exemplify the trend of leveraging geology to flexibly supply the energy grid.

10. Implications for Society and Professional Training

The transformation from hydrocarbon geology to clean storage geology has academic, professional, and ethical implications. Prestigious universities like the University of Texas at Austin, the University of Aberdeen in Scotland, and the Norwegian University of Science and Technology (NTNU) have started redesigning curricula to train geologists and engineers with skills in both hydrocarbon exploration and CCS or hydrogen storage.

Professional Implications

In the professional realm, service companies and consulting firms specializing in petroleum geology are diversifying their offerings. Many now provide feasibility studies for CO₂ injection, hydrogen infrastructure design, and even develop simulation software tailored to these new applications.

Civil Society’s Role

Civil society is also called to action. Understanding subsurface dynamics and the magnitude of climate challenges can encourage public debate on which energy sources to support and how to ensure environmental safety. Science journalism, geological museum exhibits, and public forums on energy transition are becoming indispensable.

11. Future and Legacy: Balancing Caution with Hope

Humanity is advancing toward a paradigm shift in energy production and consumption. While the climate crisis urges us to accelerate the adoption of renewable energy, there is also an acknowledgment that oil and gas will remain part of the global economy for a few more years or decades. During this transition, the capacity of sedimentary rocks to seal CO₂ or store hydrogen could be the key to managing global warming and achieving a sustainable energy transition.

Sustainability Perspective

The greatest challenge lies in maintaining a focus on sustainability. CCS and hydrogen storage are not magic solutions; they require rigorous controls, continuous investment, transparency, and regulatory frameworks that guide actions toward the common good. Ultimately, the Earth will not adapt to human whims; we must adapt to its physical limits and rhythms, where a million years is but a geological blink.

12. Conclusions: A Comprehensive View of the Energy Future

Sedimentary rocks, which have served as a source of hydrocarbons and a foundation for industrial progress for centuries, now emerge as a cornerstone in the global strategy to address the climate crisis. Their ability to retain CO₂ and serve as repositories for hydrogen opens the door to transitional solutions that, when well-managed, can accelerate the shift to a clean and sustainable energy model.

• Geological Perspective: Precise data on porosity, permeability, fracture pressure, and seals are crucial to avoid leakage risks and accurately calculate storage capacity.

• Technological Perspective: Continuous innovation is needed in carbon capture processes, the development of more efficient electrolyzers, and monitoring methods for underground injection.

• Economic and Political Perspective: Adequate incentives, clear regulations, and inclusive governance must be established to ensure the security and success of large-scale projects.

• Cultural and Social Perspective: Promoting education and public communication on these issues is urgent, as is the participation of communities in planning projects that affect their environment.

Ultimately, the deep history of the Earth intertwines with our own. Beneath the surface lies the fossil legacy that powered our development, as well as the keys to a future that honors the planet's life and diversity. Just as these rocks formed layer upon layer, social and technological transformation requires the layering of collective will, visions, and learning. Only through such reconciliation with what we are and what we have been can we move toward a more harmonious relationship with the Earth.

References for Further Study

1. IPCC (2021-2022): Sixth Assessment Report (AR6). Section on emissions reduction and carbon capture scenarios.

2. IEA (2022): Special Report on Carbon Capture, Utilization, and Storage. Data on global storage capacity in sedimentary formations.

3. EIA (2023): International Energy Outlook. Fossil fuel consumption statistics.

4. IRENA (2021-2023): Global Hydrogen Reports. Projections on the expansion of green hydrogen.

5. North American Carbon Storage Atlas (NACSA): Studies on injection capacity in U.S. and Canadian sedimentary basins.

6. Underground Sun Storage Project (2021-2023): European research on hydrogen injection into underground formations.

7. CarbFix (2021-2022): Icelandic project on CO₂ mineralization, with results in basalt that inspire studies in other lithologies.