Fill in the blanks! Enter the "water dungeon"!

On March 19, my country's first seabed carbon dioxide storage and reinjection well was officially drilled, marking that my country has initially formed a complete set of drilling and completion technologies and equipment systems for offshore carbon dioxide injection, storage and monitoring, filling the gap in my country's offshore carbon dioxide storage technology.

Written by reporter Zhao Tianyu, Photo and text editor Chen Yongjie

Interview experts:

Chen Jianwen (Researcher at Qingdao Institute of Marine Geology, China Geological Survey)

Cheng Guoming (Senior Engineer, China Institute of Geological Environment Monitoring)

According to multiple media reports, on March 19, my country's first seabed carbon dioxide storage and reinjection well was officially drilled, marking that my country has initially formed a complete set of drilling and completion technologies and equipment systems for offshore carbon dioxide injection, storage and monitoring, filling the gap in my country's offshore carbon dioxide storage technology.

▲CCUS technology is one of the important technical options for coping with global warming in the future. (Photo source: China.com)

Carbon Capture and Storage (CCS) technology refers to the process of separating carbon dioxide from industrial or related emission sources, transporting it to a storage site, and isolating it from the atmosphere for a long time. This technology is considered to be the most economical and feasible way to reduce greenhouse gas emissions and mitigate global warming on a large scale in the future. CCUS (Carbon Capture, Utilization and Storage) technology is a technology that captures and purifies carbon dioxide based on CCS technology, and then puts it into a new production process for recycling or storage. This technology is one of the important technical options for responding to global warming in the future.

At present, my country's CCUS technology is still in the stage of building demonstration projects, and will gradually move towards commercialization and scale in the future. However, for the general public, CCUS technology is relatively unfamiliar, and they know very little about this revolutionary clean development technology, which urgently needs to be interpreted and popularized.

CCUS:

Important solutions to address climate change

Carbon dioxide is the most important gas causing the greenhouse effect. With the progress of scientific research on atmospheric governance, a new theory has been proposed - since most of the carbon dioxide emitted by humans is released from fossil energy buried underground, can it be buried back underground?

CCUS technology has not been around for long, but it has been seen as an important solution to global warming. The entire process can be simply summarized as collection, transportation, storage, and use.

"Collection" refers to carbon dioxide capture, which is the process of separating carbon dioxide from industrial production, energy utilization or the atmosphere for subsequent treatment. It is mainly divided into pre-combustion capture, post-combustion capture, oxygen-enriched combustion, chemical chain capture and direct capture from the atmosphere.

At present, the commercial operation of carbon capture is relatively mature, with many companies in the industry chain, and the global annual capture capacity exceeds 40 million tons. It has even attracted Internet companies such as Tencent to join the market and cooperate with Icelandic carbon storage company Carbfix to build the first carbon dioxide mineralization storage demonstration project in China.

"Transportation" refers to the transport of carbon dioxide. The captured carbon dioxide must be transported to a suitable location for storage. It can be transported by car, train, ship or pipeline. Since there is a risk of leakage during the storage of carbon dioxide, real-time monitoring of the carbon dioxide migration process has become a hot topic in the international academic community.

"Storage" refers to the storage of carbon dioxide, which is to inject the captured carbon dioxide into deep geological reservoirs to isolate the carbon dioxide from the atmosphere for a long time, thus entering a "dormant state". Generally speaking, it can be divided into two categories: geological storage and marine storage.

▲CCUS National Demonstration Project in Huang 3 Area of ​​Changqing Oilfield, PetroChina (Photo source: China.com)

"Use" refers to the utilization of carbon dioxide, which is the process of realizing resource utilization of captured carbon dioxide through engineering and technical means, realizing the true meaning of "turning carbon into treasure".

Data from the International Energy Agency shows that CCUS technology can reduce carbon dioxide emissions by 6.9 billion tons per year in the future. After 2050, it will also help offset "necessary emissions" of carbon dioxide, and its offsetting effect will account for 15% of the cumulative carbon dioxide emissions reductions by 2070.

There are still technical barriers in the storage link

In the CCUS industry chain, carbon dioxide storage is the most important link and also the most technically difficult part. There is currently no large-scale commercial route formed internationally and it is still under continuous exploration.

For example, geological storage generally involves injecting carbon dioxide in a supercritical state (a mixture of gas and liquid) into geological structures. Oil fields, gas fields, saline layers, and unexploitable coal mines all meet these conditions. Among them, carbon storage in deep saline layers and depleted oil and gas reservoirs is the most mature technology. Saline layers, in particular, are widely distributed and have large storage capacity, and are considered the best sites for geological storage.

Although land storage technology is relatively mature at present, there are some safety hazards in the storage process of carbon dioxide due to changes in reservoir stress fields and the unpredictability of geological structures.

The most famous is the Gorgon project in Western Australia, which started producing natural gas in March 2016, but did not start up its CCS equipment until August 2019, three and a half years later than planned.

▲Gorgon Project in Western Australia (consisting of a natural gas production plant and CCS equipment) (Photo source: China.com)

The reason was that an inspection at the end of 2017 found that there was excess water in the pipeline between the factory's liquefied natural gas plant and the water injection well, causing leakage and corrosion of valves and pipelines, and sand blocked the underground gas injection wells, seriously damaging the pressure management system.

As far as my country is concerned, the current annual carbon dioxide emissions are about 10 billion tons, of which the 11 coastal provinces (cities) account for nearly half. However, due to the small area and scattered distribution of terrestrial sedimentary basins in these areas, the geological conditions suitable for carbon sequestration are relatively poor, and the storage potential is limited, so "ocean storage" has become a new path.

Marine geological carbon sequestration refers to transporting CO2 to a site in the ocean by ship or pipeline and injecting it into the geological body below the seabed for storage. Chen Jianwen, a researcher at the Qingdao Institute of Marine Geology under the China Geological Survey, explained that the geological sequestration potential of marine carbon dioxide is great because there is a thick and widely distributed saltwater layer below the seabed.

The specific method is that "the captured or separated carbon dioxide will be sent to the offshore drilling platform, and the compressor on the platform will pressurize the carbon dioxide to make it reach a supercritical state, and finally seal it into geological bodies such as deep saline layers below the seabed through injection wells." Chen Jianwen said that China already has the Enping 15-1 demonstration project in the Pearl River Mouth Basin, and is currently drilling injection wells. It is planned to inject 300,000 tons annually, and the storage volume will reach 1.5 million tons in 5 years.

▲A panoramic view of China's CCUS technology (Image source/2021 China Carbon Dioxide Capture, Utilization and Storage (CCUS) Annual Report)

Regarding the outside world's doubts that "offshore storage is not safe" and "offshore storage affects the ecological environment", Chen Jianwen said that there is no direct evidence that marine storage will pollute the ecological environment. For example, the Sleipler project in the Norwegian waters has been carrying out seabed storage since 1996. The engineering demonstration in the first five years proved that it was safe. Since then, commercial operations have been carried out and it has been injected for 27 years. It is still being injected and no abnormalities have been found. Japan injected 300,000 tons in the waters near Hokkaido from 2016 to 2019. So far, it has been monitored and no safety risks have been found.

Why is ocean storage more "safe"? Chen Jianwen said that the seawater cover can not only prevent carbon dioxide from being directly discharged into the atmosphere when it leaks, but the additional seawater pressure also reduces the requirements for the sealing of the cover layer, making the carbon dioxide stored below the seabed more stable. Due to the long-term seawater exchange, the chemical composition of the pore fluid in the seabed strata is closer to that of normal seawater, which can reduce the risk of leakage caused by fracture activity induced by pressure imbalance during carbon dioxide injection.

“Turning Carbon into Treasure”

How can carbon dioxide be used?

In addition to technology, the cost of carbon dioxide storage is also a concern for the outside world. The IPCC (Intergovernmental Panel on Climate Change) believes that CCUS can only be promoted on a large scale when the total cost of capturing and storing CO2 drops to US$25-30 per ton (approximately RMB 125-200 per ton).

However, excluding the costs of transportation and storage, the capture cost alone is currently about US$11-57 per ton (about RMB 65-400) abroad, while the current cost in my country is as high as RMB 300-900 per ton.

▲my country's first CO2 storage and reinjection well located on the seabed (Photo source: CNOOC official website)

Cheng Guoming, a senior engineer at the China Institute of Geological Environment Monitoring, believes that after the technical problems of carbon dioxide are gradually overcome, the cost will be the focus of the industry in the future. At present, the price of carbon storage is much higher than the price of carbon sinks, and companies are more willing to participate in the latter. Unless the cost is controlled, there will be great resistance to commercialization in the true sense.

"Carbon storage is not economical in China at present, but it has been proven to be economically competitive abroad," said Chen Jianwen. Cost expenditure is closely related to relevant policies, and policies will also affect carbon market prices. From a long-term perspective, the economic feasibility will gradually improve after carbon peak, and the overall trend is optimistic.

On the other hand, in addition to carbon storage, more than 80 companies around the world have begun to study another new way to use carbon dioxide - recycling and reuse. This is not only a win-win climate strategy, but may also become a new track in the CCUS field.

For example, in the field of oil exploration and production, using carbon dioxide to enhance crude oil recovery is currently the most widely used application scenario for carbon dioxide utilization technology. The revenue from increased crude oil production can offset the project costs, and the economic feasibility is high. Carbon dioxide displacement of coalbed methane technology can also significantly increase coalbed methane recovery.

Chemical products are also an important scenario for the reuse of carbon dioxide, which is very diverse in daily life, such as the production of beer and carbonated beverages; making dry ice for food refrigeration and transportation; synthesizing fine chemicals such as organic small molecules or common chemicals such as urea and hydrochloride.

At present, the construction of direct air carbon capture (DAC) plants, that is, plants that capture carbon dioxide directly from the air, has started abroad. It is expected that by 2030, 85 tons of carbon dioxide can be captured annually, and by 2050, 980 tons of carbon dioxide can be captured annually.

Perhaps one day, we will use natural gas filled with waste carbon dioxide, use dry ice supplied by CCUS technology to refrigerate food, drink canned beer and cola made with CO2 emitted by factories, and truly integrate low carbon into our daily lives. By then, you will find that CCUS is not far from you and me, and it will be a very beautiful scene.

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Produced by: Beijing Science and Technology News | Beijing Science and Technology Media

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