Among the network of yellow pipelines that pierce the sea floor beneath the platform, one green pipeline stands out. It is through this pipe that liquid carbon dioxide (CO2) is injected into seabed. The pipe is part of China's first offshore million-ton carbon storage project, which went into operation on June 1. The project is designed to store more than 1.5 million tons of CO2 in total, equivalent to planting nearly 14 million trees.

The project captures and processes CO2 generated during the oil drilling process and then injects it into a domed geological structure at a depth of approximately 800 meters below the seabed and at a distance of more than 3 km from the platform. It takes just 20 minutes for carbon to be captured, liquidized and to reach the storage structure. The technologies applied in the process belong to a group known as carbon capture, utilization and storage (CCUS) technologies.

While the vast majority of the world's offshore oil and gas fields do not contain high volumes of CO2, estimates hold that the Enping 15-1 oilfield would release more than 800 million cubic meters of the gas if no capture and storage project was put in place. More than 20 of China's undersea oil and gas fields contain similarly high amounts of CO2 and, together, they contain around 99 billion cubic meters of the greenhouse gas.

Viable options for the storage of CO2 include old oil and gas fields that have been used up, coal beds and layers of porous and permeable sedimentary rocks saturated with salty water, known as saline aquifers.

Deep saline aquifers that have a diameter of more than 10 km and are dome-shaped are among the most suitable for storing CO2. The liquid CO2 injected into the aquifer will rise to the top of the dome as its density is lower than the salt water under the seabed. The thick, impermeable or low-permeability layer at the top of the bowl prevents the CO2 from leaking out, ensuring it is effectively contained.

Prospects 

The use of CCUS technologies is an internationally recognized method of reducing carbon emissions and addressing global warming.

According to the International Energy Agency (IEA), CCUS facilities have been operating for decades in certain industries, such as natural gas processing and fertilizer production, where the CO2 can be captured at relatively low cost; but in other areas, including cement and steel production, CCUS remains at an early stage of development. IEA estimated that global annual carbon emission reductions using CCUS technologies will reach 1.6 billion, 4 billion and 7.6 billion tons by 2030, 2035 and 2050, respectively, accounting for 4.7, 11.8 and 22.4 percent of total global carbon emissions in 2020.

CCUS will play an important role for China to reach its goals of peaking its carbon emissions before 2030 and achieving carbon neutrality before 2060. China Geological Survey, an institution of geological survey, scientific research and information service, revealed in January that CO2 storage capacity in China's sea areas is projected to be 2.58 trillion tons, about 225 times China's CO2 emissions last year, which was 11.48 billion tons according to IEA data.

China has made remarkable progress in CCUS development in the past decade. "With the continuous development of CCUS technologies, the number of domestic CCUS demonstration projects increased from 49 in 2021 to 104 in 2022," Zhang Xian, an official with the Administrative Center for China's Agenda 21 (ACCA21), told Science and Technology Daily. The ACCA21, affiliated with the Ministry of Science and Technology, has promoted the implementation of China's Agenda 21, the overall strategy of the country's sustainable development formulated based on its own conditions. The strategy was approved by the State Council in 1994 following the adoption of Agenda 21, an intergovernmental sustainable development action plan, by the United Nations Conference on Environment and Development in 1992.

Companies such as energy and chemical company China Petrochemical Corp. (Sinopec) and oil company China National Petroleum Corp. have developed CCUS demonstration projects, with petroleum, power generation, coal chemical and chemical fertilizer industries being the main sources of carbon captured and stored.

The market prospects for CCUS in China are promising. According to a report published by the Zhongshang Industrial Research Institute in March, the CCUS market in China is projected to reach more than 20 billion yuan ($2.8 billion) by 2025 and more than 330 billion yuan ($46.4 billion) by 2050, translating to an average annual growth rate of 11.87 percent.

However, the commercialization of CCUS technologies still faces many difficulties and challenges.

The cost of building and maintaining carbon capture and storage facilities is high. According to CNOOC, it cost 257 million yuan ($36.1 million) to build the carbon capture and storage facilities for Enping 15-1 and their maintenance costs around 2.5 million yuan ($351,528.4) every year. In China, the current cost of capturing and storing one ton of CO2 is 500 to 1,000 yuan ($70.3 to 140.6). However, the cost of the whole CCUS process is expected to drop to 310-770 yuan ($43-108) per ton of CO2 by 2030 and to 140-410 yuan ($20-58) per ton of CO2 by 2060, according to a report released in August 2021 by the Chinese Academy for Environmental Planning.

In addition to cost, technological innovation is a key factor affecting the scale production of the CCUS industry.

China's CCUS technologies still requires many breakthroughs. To realize the commercialization and scale production of the CCUS industry, research needs to be strengthened, costs reduced and demand stimulated.

In spite of the difficulties, companies and governments are working together to promote the commercialization of these technologies.

Last June, CNOOC, the Guangdong Provincial Development and Reform Commission, multinational oil and gas companies Shell and ExxonMobil, and a global group of energy and petrochemical companies signed a memorandum of understanding to explore the feasibility of developing a CCUS hub in Daya Bay in Huizhou, Guangdong, to capture up to 10 million tons of CO2 a year. If successful, it will be China's first offshore large-scale CCUS hub and will significantly reduce the CO2 emissions of enterprises in the area.

Qi Meisheng, General Manager of CNOOC's Shenzhen branch, said the corporation will continue to strengthen scientific and technological research to promote and upgrade CCUS technologies.

(Print Edition Title: A Green Alternative) 

Copyedited by G.P. Wilson 

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