On April 3, a carbon dioxide pipeline ruptured in southwestern Louisiana, near the rural town of Sulphur, releasing more than 100,000 gallons of carbon dioxide. Officials in Calcasieu Parish set up roadblocks and issued a shelter in place warning to local residents, urging everyone within a quarter mile to close doors and windows to keep out the gas, which can be lethal in high concentrations.

No injuries were reported, this time. But it was not the first or even the largest such carbon pipeline leak in recent years, during a time of rapid growth of CO₂ pipelines and carbon capture projects, funded with federal subsidies meant to help combat climate change.

In 2020, a CO₂ pipeline rupture in Yazoo County, Mississippi sent 45 people to the hospital. Two hundred residents needed evacuation, which was made more difficult by car engines stalling because of the lack of oxygen.

Both leaks had one thing in common: the pipelines were owned by the same company, Denbury Inc.  

Denbury is one of the largest companies producing oil though enhanced oil recovery, which uses CO₂ to dislodge oil remnants from nearly depleted stores. The company owns an extensive network of CO₂ pipelines to supply its oil fields. However, data from the Pipeline and Hazardous Materials Safety Administration (PHMSA) shows Denbury is responsible for more CO₂ leakage than any other CO₂ pipeline company.  

Since 2010, there have been 76 incidents involving CO₂ pipelines reported to PHMSA, collectively releasing nearly 67,000 barrels of CO₂ into the air. Denbury was responsible for 12, releasing nearly 54,000 barrels, or 81 percent of that amount.  

Denbury, which was acquired by ExxonMobil in 2023, operates more than 1,100 miles of CO₂ pipelines in the Rocky Mountains and the Gulf Coast. Denbury’s pipelines carry CO₂ extracted from natural underground stores of CO₂, or captured from industrial sources, such as gas processing plants, forming a complex network of interconnected pipelines with multiple collection and delivery points.

Three of the five largest CO₂ pipeline leaks reported to PHMSA involved Denbury’s CO₂ pipelines, including the April 3 leak in Sulphur, which is number five at just over 2,000 barrels. On average, a leak from one of Denbury pipeline released 4,700 barrels of CO₂. The average non-Denbury leak released only 200 barrels of CO₂.  

At low concentrations, CO₂ exposure can cause headaches, dizziness, difficulty breathing, and even confusion or mental clouding. At higher concentrations, CO₂ can cause unconsciousness within minutes. CO₂ is heavier than air and tends to collect in low-lying areas and confined spaces where it can easily overwhelm the unsuspecting. A large, sudden influx of CO₂, such as a pipeline leak, can be catastrophic for the people who live nearby.

In October 2020, Denbury’s Delta pipeline ruptured near Satartia, Mississippi, releasing more than 41,000 barrels of CO₂ with enough force to create a 40-foot crater – injuring dozens of people.  

According to the investigation report, initial assessments showed that indoor CO₂ concentrations reached up to 28,000 parts per million (ppm). The National Institute for Occupational Safety and Health recommends a short term (15 minute) exposure limit of 30,000 ppm.  

Denbury’s pipeline leaks are so significant that even if the Satartia rupture were excluded, Denbury would still be responsible for about half of the CO₂ leaked into the air from pipelines.

Denbury’s pipeline network is particularly extensive, making up about one-fifth of the more than 5,000 miles of CO₂ pipelines currently operating in the United States. However, Kinder Morgan, another company delivering CO₂ to oil fields, also operates more than a thousand miles of CO₂ pipelines in Colorado, Utah, Texas, and New Mexico. While Kinder Morgan has reported 29 incidents since 2010 (more than twice Denbury with 12 incidents), its leaks tend to be much smaller, releasing about 128 barrels on average (cumulatively, about 3,700 barrels of CO₂ since 2010).

Denbury’s recent incidents have also revealed weaknesses in the warning systems and emergency response planning for CO₂ pipelines. In Mississippi, Denbury’s modeling had not anticipated a pipeline leak that could reach Satartia, which meant that local responders were not prepared for a CO₂ leak.  

In Louisiana, many residents were not aware of the pipeline leak until hours later. Sulphur resident Cindy Robertson, who runs local nonprofit Micah 6:8 Mission, said she only heard about it later that evening when a friend forwarded her a news article about officials lifting a shelter-in-place order she had not seen.  

“I went to sleep with the thought in my head, ‘Is more of it going to leak, are there going to be more problems, how are we going to be notified?’” Robertson said. “I had nightmares all night.”

In Denbury’s online reports, the company claims that it “takes many preventive measures to promote safe, reliable operations of our pipelines,” including by having 24-hour pipeline monitoring, as well as aerial and ground surveillance.  

However, these methods may not be enough to detect leaks consistently. About one in four leak incidents was not first detected by local operating personnel or an automated monitoring system. In Sulphur, emergency personnel notified Denbury of the leak, and pipeline operators arrived on scene two hours after the local fire department. In two other cases, Denbury was notified of a problem by the public.  

Denbury’s pipeline leaks are also by far the most expensive. Since 2010, CO₂ pipeline leaks have cost about $6 million in total, including property damage and lost revenue from escaped CO₂, of which Denbury makes up $4.8 million. These numbers also include more than $334,000 in emergency response and environmental remediation costs, and nearly $300,000 of that was made up by Denbury alone.  

Denbury has announced plans to expand their pipeline network even further to include 12 proposed carbon sequestration sites in Louisiana, Texas, Mississippi, Alabama, Montana, and Wyoming, where carbon dioxide will be injected underground for “permanent” storage instead of extracting oil. These expansions will require even more pipeline construction, not only to connect sequestration sites to existing pipelines, but to transport even more CO₂ emissions captured from industrial facilities.

Denbury has agreements to collect, transport, and store CO₂ emissions from at least eight industrial facilities, totaling up to 20 additional million metric tons of CO₂ per year. Denbury’s parent company, ExxonMobil, also has agreements to store CO₂ emissions from at least one ammonia plant, which may also incorporated into Denbury’s facilities.

As these plans for large pipeline networks come to fruition, these large incidents may become increasingly more common. Denbury is not the only company with plans for a large interstate CO₂ pipeline network – another is Summit Carbon. But Denbury’s safety record is especially concerning considering one of Denbury’s biggest pipelines – the Green Pipeline, which runs from Texas to Louisiana -- currently only operates at 20 to 30 percent of its total capacity,  These leaks may become larger or more frequent as the pipelines take on more CO₂ and operate at full capacity.  

PHMSA is working on updating its standards for CO₂ pipelines. Details are not yet available, but the new rules will address operational safety issues and emergency response planning. PHMSA’s proposal is expected to be released for public comment in the coming months. As pipeline companies move forward with their ambitious plans for carbon pipelines, these new regulations will be key to ensuring their safety over the next decades.

Lead photo: A Calcasieu Parish Policy Jury photo shows CO₂ vapor erupting from Denbury’s Green carbon dioxide pipeline near Sulphur, Louisiana, on April 3, 2024.