Surreal illustration of CO2 plumes and seismic waves in a deep-sea carbon storage environment.

Sleipner's CO2 Injection: What 20 Years of Monitoring Reveal About Carbon Storage

Soraya Malik in Climate & Environment December 2025 • 5 min read.

"A deep dive into two decades of groundbreaking research at the Sleipner project, revealing critical insights for safe and effective carbon capture and storage."

The Sleipner CO2 injection project, launched in 1996, stands as a pioneering effort in offshore Carbon Capture and Storage (CCS). With over 16 million tonnes of CO2 injected beneath the seabed, it has provided invaluable insights into the long-term behavior of stored carbon dioxide. The project's success stems from the dual interpretation of seismic and gravimetric monitoring surveys, allowing scientists to quantify changes in CO2 mass and plume geometry over time.

Sleipner's legacy extends beyond its immediate impact. The project's learnings have directly influenced guidelines for future CCS initiatives, emphasizing the importance of tailored monitoring strategies that consider specific site conditions and potential risks. The selection of monitoring technology, along with the timing and extent of surveys, should be carefully considered to account for the long-term nature of CCS projects.

Initially driven by Norway's CO2 emissions tax and a desire to minimize environmental impact, the Sleipner project has evolved into a critical research platform. The continuous monitoring and data analysis have not only ensured the safe storage of CO2 but have also significantly advanced our understanding of subsurface CO2 behavior.

Unlocking the Secrets of Subsurface CO2: Seismic and Gravimetric Monitoring at Sleipner

Surreal illustration of CO2 plumes and seismic waves in a deep-sea carbon storage environment.

Sleipner employs a comprehensive geophysical and environmental monitoring program. Key to this program is the repeated acquisition of 3D seismic surveys. Ten 3D seismic surveys and four gravity surveys have been conducted, providing a detailed picture of CO2 movement and distribution within the storage unit. These surveys, combined with a baseline survey from 1994, create a unique dataset for imaging plume development.

Seismic monitoring works because of the strong contrast in sonic velocity between supercritical CO2 and the surrounding brine-filled reservoir. This contrast allows seismic waves to clearly image the boundaries of the CO2 plume as it migrates through the subsurface. While seismic acquisition technology has advanced significantly over the years, the core principle remains the same: using sound waves to map the location of the injected CO2.

Conformance monitoring: Ensuring that the behavior of CO2 in the reservoir is understood.
Containment monitoring: Ensuring that CO2 stays within the storage unit.
Contingency monitoring: Assessing effect of contingency measures in the case of leakage.

Complementing seismic data, gravimetric monitoring offers an independent measure of density changes, directly related to CO2 saturation. By installing permanent seabed benchmarks and conducting repeated gravity surveys, scientists can track changes in subsurface density as CO2 displaces the original formation fluids. Combining seismic and gravimetric data provides a more comprehensive understanding of CO2 behavior, enabling researchers to estimate CO2 density and dissolution rates within the formation water.

Sleipner's Enduring Impact: Shaping the Future of Carbon Storage

The Sleipner project has proven that remote geophysical monitoring is a reliable tool for ensuring the safe and effective storage of CO2. The continuous monitoring efforts have demonstrated that the injected CO2 remains securely contained within the storage unit, validating the viability of CCS as a climate mitigation strategy.

The project's success highlights the importance of downhole pressure and temperature gauges for understanding in-situ conditions, as well as the value of repeated seismic surveys for containment and conformance monitoring. By combining gravimetric and seismic data, researchers can gain a more complete picture of CO2 mass change and plume geometry, enabling more accurate predictions of long-term CO2 behavior.

As the world continues to explore CCS as a means of reducing greenhouse gas emissions, the lessons learned from Sleipner will be invaluable. The project's monitoring strategies, data analysis techniques, and insights into subsurface CO2 behavior will help guide future CCS projects and ensure the safe, long-term storage of carbon dioxide.

About this Article -

This article was crafted using a human-AI hybrid and collaborative approach. AI assisted our team with initial drafting, research insights, identifying key questions, and image generation. Our human editors guided topic selection, defined the angle, structured the content, ensured factual accuracy and relevance, refined the tone, and conducted thorough editing to deliver helpful, high-quality information.See our About page for more information.

This article is based on research published under:

DOI-LINK: 10.1016/j.egypro.2017.03.1523, Alternate LINK

Title: 20 Years Of Monitoring Co2-Injection At Sleipner

Subject: General Medicine

Journal: Energy Procedia

Publisher: Elsevier BV

Authors: Anne-Kari Furre, Ola Eiken, Håvard Alnes, Jonas Nesland Vevatne, Anders Fredrik Kiær

Published: 2017-07-01

Everything You Need To Know

How does the Sleipner project monitor the injected CO2, and what specific data is collected to understand its behavior?

The Sleipner project, which began in 1996, injects CO2 into a subsurface reservoir. Over 16 million tonnes of CO2 have been injected. The project employs both seismic and gravimetric monitoring to track the CO2 plume. Ten 3D seismic surveys and four gravity surveys have been conducted, along with a baseline survey from 1994. This data helps scientists understand how CO2 behaves underground, but does not contain any details about chemical reactions of CO2 with the rocks.

What are the key differences between seismic and gravimetric monitoring at Sleipner, and how do these methods complement each other in tracking CO2?

Seismic monitoring at Sleipner relies on the sonic velocity contrast between supercritical CO2 and the surrounding brine-filled reservoir. This difference allows seismic waves to image the CO2 plume boundaries. Gravimetric monitoring, on the other hand, measures density changes related to CO2 saturation. Combining these methods offers a more complete understanding of CO2 behavior, helping estimate CO2 density and dissolution rates within the formation water. Neither technique on its own provides information about the purity of the CO2 stream being injected.

Beyond simply tracking the CO2 plume, what are the primary objectives of the monitoring program at the Sleipner project?

The Sleipner project has three main monitoring objectives: conformance monitoring to understand CO2 behavior, containment monitoring to ensure CO2 stays within the storage unit, and contingency monitoring to assess the effect of any necessary corrective actions if a leak were to occur. These monitoring objectives guide the selection of appropriate monitoring technologies and survey strategies. These objectives do not cover monitoring of the effect on marine life and the immediate seabed.

In what ways has the Sleipner project informed or influenced the design and implementation of subsequent carbon capture and storage projects?

Findings from the Sleipner project have influenced guidelines for future Carbon Capture and Storage initiatives. The project highlights the importance of tailoring monitoring strategies to specific site conditions and potential risks. Careful consideration should be given to monitoring technology selection, survey timing, and the extent of surveys. The guidelines do not include details of how to handle public perceptions of CCS.

What specific technologies and techniques are employed at the Sleipner project to ensure the long-term integrity and safety of the CO2 storage site?

The Sleipner project primarily uses seismic and gravimetric monitoring to track the movement and distribution of CO2 underground. Seismic surveys use sound waves to map the location of the CO2 plume, while gravimetric surveys measure changes in subsurface density to determine CO2 saturation. These remote geophysical monitoring techniques offer a reliable way to ensure the safe and effective storage of CO2. These techniques do not provide direct measurements of the mechanical integrity of the caprock.