*4.2.2 CO2 injection*

CO2 might be injected directly into the reservoir if the pipeline pressure is adequate. However, it is likely to bring CO2 onto platform for control pressure or to lift its pressure; certain design considerations should be considered. Below are the injection facilities' operation conditions and the process flow diagram of field test of CO2 injection in Nagaoka, Japan [43]. Some operation details of injection facilities in Nagaoka are summarized in **Table 1**.

### *4.2.3 Risers, emergency shut down valve (ESDV), compressors, and pumps*

Risers are the piping that transports the fluid between the offshore platform and the seabed. Flexible risers are used especially on floating production installations. ESDV is placed between the moving pipe infrastructure and the riser to the platform as a safeguard gadget to guarantee no leakage of CO2 when there is failure in platform. It is likely found on the seabed where there is the possibility of heavy things to be dropped on the pipeline underneath during the lifting operation work. Moreover, it is designed to counter any structural failure on the platform and any upstream failure where it will cause the valve to close.

Pressure issue related to CCS projects may require extra pumping units due to higher pressure required over long distance. In the event that the pressure drops along offshore pipeline, usually pumps would be placed on an offshore platform [44].

### *4.2.4 Fluid separation*

Due to the nature of CO2-EOR patterns, the water production is high, thus leading to the need for large separation capacity with inlet separators dominated with water rather than oil. Moreover, separation is harder because of scale, emulsion, ESP or gas lifting, and asphaltenes. A large CO2 reinjection compressors are needed due to high CO2 production that resulted from back produced CO2 in the system.
