**5. Prospect of offshore chemical EOR potential**

At present, the offshore chemical flooding technologies represented by polymer flooding and surfactant-polymer flooding have achieved successful field tests and applications in China, and their technical reliability and economic effectiveness have been confirmed. However, it still faces some important challenges, including how to affordably develop the movable heavy crude oil with formation viscosity above 150 mPa s, how to effectively contain the water channeling to further improve oil recovery, how to achieve efficient treatment of polymer-bearing produced fluid on offshore platforms, etc. Therefore, it is necessary to continuously explore and develop novel offshore chemical flooding technologies, such as the heavy oil activator flooding, intelligent chemical flooding, and their combination technology.

As for the field application of the offshore chemical flooding in China, the cumulative oil increment is estimated to be 8.23 million cubic meters in the three oil fields currently performed. The total economic benefit is 9.3 billion yuan, and the

input-output ratio is 1:3.7. In addition, according to the present offshore chemical potential evaluation and plan, 41 reservoir units are suitable for chemical flooding in Bohai Bay, whose oil recovery could be improved by 6.53% according to prediction [27, 28]. At the same time, China offshore chemical flooding technology and field applications provide valuable and practical reference for domestic and overseas counterparts. TOTAL and Chevron have, respectively, implemented polymer flooding tests in fields in West Africa, the North Sea, and Malaysia [28]. All of these attempts will further promote the progress of offshore chemical flooding and provide technical support for enhancing oil recovery in offshore oil fields.
