Assessing Geomechanical Risk at Geologic Carbon Storage Sites
In the pursuit of achieving net-zero emissions by 2050, hundreds of millions of tons of carbon dioxide (CO2) are expected to be injected into the deep subsurface in the United States over the next few decades. This marks a pivotal step in the carbon capture, transport, and storage industry, which will transition from demonstration projects to large-scale deployment.
Over the last 15 years, researchers at Pacific Northwest National Laboratory (PNNL) have been actively involved in developing the science and understanding of risks at geologic carbon storage sites, contributing to the identification, quantification, and management of these risks. Recently, a PNNL team led the development of a cloud-computing tool to assess geological sites and to predict and manage the geomechanical risks of carbon storage operations—supporting the nation’s carbon reduction goals.
The web version of the State of Stress Analysis Tool (SOSAT), developed under the National Risk Assessment Partnership (NRAP) for the Department of Energy Office of Fossil Energy and Carbon Management, was launched to the public in March 2024.
“Geologic carbon storage changes the state of stress in the subsurface,” said Jeff Burghardt, PNNL Earth scientist and SOSAT lead developer. “Our hope is that this tool will be an important part of building stakeholder confidence in future projects and that—by using SOSAT—they know they have done their due diligence, accounted for the uncertainties, and did a rigorous job of quantifying and managing the risks.”
The cloud-computing, user-friendly tool has an interactive map with publicly available regional stress environment data. It takes available field measurements within an area of interest and quantifies parameter uncertainty, such as rock mechanical properties and formation temperature. Based on the uncertainty of each parameter and constrained stress field, SOSAT generates millions of random stress samples to determine the probability of fault activation and hydraulic fracturing resulting from pressure changes associated with injecting CO2 4,000 feet or more underground, which is over three times the height of the Empire State Building.
Assessing the probability of fault activation is crucial to understanding the potential for seismicity and leakage, and how operations could be managed to reduce these risks.
Though recently launched to the public in a web application, SOSAT has been available for experts in the field since 2019 to meet industry and research needs for a tool to aid decision-making for geological carbon storage. Burghardt used statistical methods accounting for uncertainties in how stress is measured underground as a starting point to develop SOSAT.
“Taking a best guess at some of the uncertainties is not good enough,” said Burghardt. “The method we use with SOSAT maps the uncertainties and quantifies all of the assumptions for an in-depth analysis, which gives us probability distribution of the feasible stresses.”
More recent releases of the SOSAT tool included a graphical user interface and have made a web-based version available to a wide array of users.
“When we started working on the NRAP project, talk about risk associated with carbon storage was relatively new,” said Delphine Appriou, geoscientist and NRAP project manager at PNNL. “Now, more than a decade later, there are several dozen projects planned in the US, so being confident that risks are understood and can be appropriately managed is incredibly important.”
The increased interest in large-scale deployment of carbon storage was a driving factor to move SOSAT to an online platform.
“It makes it more accessible and useful to the broader carbon storage community in this important moment in time,” said Appriou.
As more people have access to the tool, Wenjing Wang, the main contributor to the web version of SOSAT, said, “Analyzing the state of stress is the first thing operators will want to do in order to understand the downstream geomechanical risks. I’m hoping this tool we launched will be the first one people think about to use to help with carbon storage operations for site selection and management in the future.”
Learn more about SOSAT, including its technical capabilities and how to access the tool, at https://www.pnnl.gov/projects/state-stress-analysis-tool.
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