Carbon dioxide capture, utilization and storage technology: carbon reduction and production increase

Today, when carbon neutrality is frequently mentioned, people are exploring the possibility of achieving energy conservation and carbon reduction in many directions. This is true of the popularity of new energy vehicles, the innovation of photovoltaic industry, and the planning of afforestation. At the same time, more carbon reduction technologies are also concerned, such as carbon dioxide capture, utilization and storage (CCUS) technology. This technology refers to the technology that captures carbon dioxide from industrial or other carbon emission sources and transports it to specific locations for use or storage. It has the characteristics of large scale emission reduction and obvious emission reduction benefits, and is known as "carbon catcher".

At present, the more mature carbon dioxide storage methods include geological storage and mineral storage. Geological storage is generally to inject carbon dioxide in the supercritical state (mixture of gas and liquid) into deep geological structures for storage. Common geological structures suitable for carbon sequestration include oil fields, gas fields, salt water layers, and non exploitable coal mines. Experts said that these natural reservoirs have large space and wide distribution. However, due to the change of reservoir stress field and the existence of natural fractures, faults and other geological structures, the risk of carbon dioxide leakage must be considered. Therefore, the academia is actively looking for a good way to conduct real-time monitoring of carbon dioxide transport process. The carbon dioxide injected into the formation can be stored for more than 1000 years at the geological storage site selected after investigation and calculation under strict management.

Geological sequestration is a simple physical sequestration method. Another mineral sequestration method requires a series of chemical reactions (mainly the exothermic reaction between CO2 and minerals containing Mg and Ca). With the help of catalyst, the gas carbon dioxide is converted into stable solid carbonate (mainly magnesite and calcite). Compared with geological storage, solid carbonate minerals have no leakage risk, can permanently store carbon dioxide and are harmless to the environment.

In August this year, China's first million ton CCUS (carbon capture, utilization and storage) project was fully completed.

Chemical enterprises are the "big spenders" of carbon emissions. Limited by product characteristics, they still need to consume a large amount of fossil energy even after improving the process and optimizing the energy structure. With the rigid emission of carbon dioxide, carbon reduction pressure is heavy. For oil fields, it is feasible to use high-purity carbon dioxide to improve oil recovery. This is also the core principle of the project operation through cryogenic and compression technologies, as well as independently developed capture equipment. After the project is officially put into operation, petrochemical enterprises can recover 1 million tons of carbon dioxide every year. The captured carbon dioxide will be transported by special transport vehicles to an oil field 80 kilometers away. There, more than 10 unmanned gas injection stations will fill nearby injection wells day and night.

So, what's the use of injecting carbon dioxide into oil fields? In fact, after the purified carbon dioxide is injected into the reservoir, it can increase the fluidity of crude oil, and also make the crude oil originally hidden in the rock crevices "show up", thus greatly improving the oil recovery. The oil displacement efficiency of carbon dioxide is 40% higher than that of water, and it is estimated that the oil increase will be nearly 3 million tons in the next 15 years.

In this cooperation mode, the utilization of carbon dioxide is not only the application of new oil displacement methods, but also the underground storage of carbon dioxide injected into the oil field. Although some carbon dioxide will escape during oil production, the primary storage rate can reach 60% to 70%. The small part that escapes will be captured by the "associated gas capture and reinjection system" independently developed by the oilfield, and reinjected into the oil well, so as to finally make the storage rate close to 100%.