Abstract: Offshore carbon dioxide (CO₂) capture and storage (CCS) is one of key technologies to cope with global climate change and reduce greenhouse gases such as CO₂, and also an important solution to achieve carbon neutrality goal of China. Offshore sedimentary basins of China have huge storage potential, and the first offshore CO₂ geological storage demonstration project has been officially launched in the Pearl River Mouth Basin of the South China Sea in 2022. Japan’s Tomakomai CCS project is the most successful offshore CO₂ geological storage project in Asia so far, and its monitoring work provides important practical references and technical experiences for the development of China offshore CCS projects. Based on this consideration, this paper comprehensively reviews the case of Tomakomai CCS project, analyzes its implementation, site monitoring items and distribution, monitoring facilities and technologies, monitoring results, etc., summarizes the successful experience of the Tomakomai CCS project and the multi-level and all-round monitoring system of land-wellbore-marine integration, aiming to help offshore CCS projects of China run smoothly, and to ensure the security and safety of the marine ecological environment.

Key words: offshore CO₂ geological storage, Tomakomai CCS project, security risk, seabed seismicity, marine environment, land
and marine integrated monitoring