A leak – but what next?

The E&E News website, part of Politico, recently published the news that the US Envi­ronmental Protection Agen­cy (EPA) issued a violation notice to the operator of the Decatur CCS pro­ject in Illinois, USA. A leak related to a monitoring well has caused around 8,000 tonnes of CO₂ to migrate up in the overburden, but it is not thought to have threatened groundwater re­sources.

The leak was detected in March this year at one of the two moni­toring wells at a depth of around 5,000 ft, but the corrosion had been known since about October 2023. The operator of the plant is Arch­er-Daniels-Midland.

It is important to note that this project is a saline aquifer injection scheme, with wells drilled to contain and inject/monitor CO₂ . The injec­tion permit for this project specifically states that “casing and cement or oth­er materials used in the construction of the well must have sufficient struc­tural strength for the life of the ge­ologic sequestration project. All well materials must be compatible with all fluids with which the materials may be expected to come into contact.” It is, therefore, a concern that corrosion has taken place to the extent that CO₂ has been able to leak.

4.5 MILLION TONNES

The Decatur CCS project has been running on and off since 2011, when the first 3-year CO₂ injection phase started. The objectives at the time were to validate the capacity, injectivity, and containment of the Cambrian-aged Mount Simon reservoir while almost 1 million tonnes of CO₂ were injected. The top of the reservoir is at approximately 1,670 m, and its thickness is 450 m. The sealing unit is the Eau Claire Shale, which attains a thickness of around 130 m. So far, a total of 4.5 million tonnes of CO₂ have been injected, and the project is thought to run for a few more years.

The incident also sparked discus­sion on social media about monitor­ing these things more efficiently and promptly. Andres Chavarria from LUNA OptaSense, commented that more and more CCS facilities are starting to be instrumented with fi­bre optic sensors in order to monitor plumes, induced seismicity and well­bore integrity.

No stop

It is of concern that wells drilled with a carbon storage project in mind cor­rode to a point where leakage occurs. However, if we want geological CO₂ storage to become a major element in mitigating anthropogenically induced climate change, let’s not use this pro­ject as an example to shut down projects but rather focus on improving both mate­rials and monitoring techniques.