Through the development of carbon capture, utilization and storage technology, an extraction area in PetroChina Liaohe Oilfield, located in Panjin, Liaoning province, has been injecting the carbon dioxide produced during the extraction process into underground storage over 3,000 meters deep. This not only effectively reduces carbon dioxide emissions, but also increases the recovery rate of petroleum.

Ma Chenglong, head of the sixth oil extraction area in Liaohe Oilfield and the person-in-charge of the CCUS cyclic injection station, said that since the trial operation of the first carbon storage facility, the 229 Block CCUS cyclic injection station, in Liaohe Oilfield in December, nearly 50,000 metric tons of liquid carbon dioxide isolated from petroleum production emissions have been injected underground.

"This is the only carbon storage facility in Liaohe Oilfield, and by 2026, it will be able to store 100,000 tons of carbon dioxide," Liang Fei, a senior engineer at the research institute, said. "The total carbon dioxide storage capacity can reach 2.36 million tons, which is equivalent to the function of reducing carbon dioxide emissions by planting a forest of 950,000 trees in an area of 10,000 mu (667 hectares)."

The construction of this carbon storage facility is an important project for Liaohe Oilfield to help reach national dual carbon targets and achieve green, low-carbon and clean development.

In September 2020, President Xi Jinping announced at the 75th United Nations General Assembly that China strives to peak carbon dioxide emissions before 2030 and achieve carbon neutrality before 2060, which is China's dual carbon goal.

Peak carbon dioxide emissions refer to the time when carbon dioxide emissions no longer increase, after which they gradually decline.

Carbon neutrality refers to offsetting carbon dioxide or greenhouse gas emissions through activities such as afforestation, achieving relatively "zero emissions".

"Liaohe Oilfield has large carbon emissions and Liaoning is also a province with high carbon emissions, making the task of carbon reduction arduous. The strategic project of carbon storage facilities in Liaohe Oilfield is not only based on favorable conditions, but also an urgent need for the national dual carbon strategic development," Wu Yi, chief expert of Liaohe Oilfield, said.

Injecting gases such as carbon dioxide underground and ensuring their stable storage without leakage places high demands on geological conditions. Wang Zhipeng, director of the injection station, said the 229 Block meets these conditions precisely — the underground rock formations have high hardness and density, and the cap rock is also firm.

Oil reserves in this area are 3.58 million tons, with the majority being heavy crude oil, which is difficult to extract. Through the operation of the CCUS cyclic injection station, not only has the carbon dioxide emissions problem been solved, but the extraction efficiency has also been increased from around 10 percent to 40 percent, Wang said.

Oil exists in different forms at different depths underground, and different geological conditions and oil states require different extraction methods. For example, in some areas, oil can be directly extracted. While in others, water injection is needed. In areas where rock formations have high density and low permeability, such as low permeable oil layers, gas injection is required to aid in oil recovery.

"The concrete floor we are standing on has high density, and it is difficult for water to pass through it. When the underground rock formations that contain oil have high density, injecting high-pressure gases like carbon dioxide can help to force out the oil stored in the formations and increase the extraction rate," Wang said.

Construction began for the CCUS cyclic injection station in the 229 Block in March last year. Since its completion in December, over 40,000 tons of carbon dioxide have been injected underground, leading to an increase of over 6,000 tons in oil production.

Liang explained that in recent years, nearly 80 percent of new geological reserves in the Liaohe region are special lithological oil reservoirs such as tight oil and shale oil, which have a large oil expansion rate and low permeability. Their carbon absorption capacity is three to four times that of water, and it has been confirmed that carbon dioxide has a significant oil displacement and energy supplementation effect, as well as good viscosity reduction effect.

It is estimated that there are 262 potential blocks suitable for CCUS applications in the Liaohe area, with a carbon storage capacity of over 200 million tons, making it a natural large carbon storage facility.

Luan Ruizhi, director of the CCUS project department at the Oilfield Technology Research Institute, said Liaohe Oilfield has the deepest burial and the most diverse types of CCUS projects in the country, which means that some problems have no domestic solutions and must be resolved independently.