ConocoPhillips has operated offshore on the Norwegian continental shelf for decades, with legacy assets including Ekofisk, Eldfisk, Embla and Tor. As part of our commitment to reduce the impact of our activities on the local marine environment, we recently assessed the water column adjacent to produced water discharges from Ekofisk and Eldfisk offshore oil and gas installations.

“Our presence in Norway dates back to the 1960s, leading up to the discovery of Ekofisk in 1969. Studies such as this, monitoring the water column, are part of our continuous quest to improve our operations and our adherence to stringent, ever-increasing environmental standards,” said Harald Lura, Senior Environmental Advisor, ConocoPhillips Norway. Ekofisk is located in the North Sea about 180 miles offshore, halfway between Norway and the United Kingdom. Eldfisk is located about 6 miles south of Ekofisk.

For the last decade, our focus has been on optimizing our processes to reduce oil-in-water concentrations in discharges of produced water, which is the water generated during oil production. Our Ekofisk operations have a long history of improving the quality of discharged water with our oil-in-water ratio declining significantly over time, and continuing to outperform regulatory requirements. In 2022, the concentration averaged 5.5 mg/L.

Determining whether these efforts have a measurable impact on the marine life in the area near our operations was the goal of a recent water column monitoring study. The study included two ConocoPhillips assets, Ekofisk and Eldfisk, which have different discharge profiles. Ekofisk has a significant discharge of treated produced water, whereas Eldfisk has a moderate discharge. Chemical accumulation and biological effect assessments were performed on caged mussels positioned at different distances downstream of treated produced water discharge sites in the North Sea.

The research occurred in two phases. In the first, monitoring rigs were placed at different stations downstream from discharge at the Ekofisk and Eldfisk oil and gas fields, as well as at two reference stations. In the second phase, the monitoring rigs were retrieved, and the mussels were analyzed to assess chemical accumulation and biological responses. As expected, hydrocarbons from the produced water were found in the mussels closest to major discharge points, but only limited accumulation was found in mussels from stations further than 1 kilometer away.

Based on biomarkers, little impact on the mussels was detected. A biomarker study objectively measures what is happening in a cell or an organism at a given moment. Hydrocarbons measured in the mussels were lower than those recorded in earlier studies at Ekofisk and also lower than predicted by models used for environmental impact assessment.

“Simply put, we did see that mussels were absorbing hydrocarbons from the produced water, but concentrations were low, and we did not identify any negative impact to them,” Lura said.

Companies operating on the Norwegian continental shelf collaborated to study the impacts of produced water discharges. The field work and reporting of results were performed by a consortium of independent researchers and subsequently reviewed by peers appointed by the Norwegian Environment Agency (NEA). The program was prepared by the operators and approved by the NEA. The study also involved collaboration between several research institutes, the Norwegian Research Institute (NORCE), the Institute of Marine Research (IMR) and the Norwegian Institute for Water Research (NIVA) together with the University of Stavanger.

Water column monitoring surveys have taken place at various offshore oil and gas fields over the last 30 years. These began as annual programs focused on chemical measurements but have evolved to become large integrated programs performed every three years, focused on chemical and biological effects. Two drivers of environmental impact on the marine environment from offshore oil and gas activities have been drill cuttings at the seabed and produced water discharged to sea following treatment. Discharge of oil in drill cuttings was prohibited in 1993 and regulations now strictly control the use of hazardous chemicals during drilling operations, but drill cuttings discharged prior to 1993 continue to be monitored. The first water column monitoring survey at Ekofisk was performed in 1999.

“We’ve operated here for more than 50 years and we expect to be here for decades to come. We care deeply about lessening impacts to marine life near our operations,” added Lura.