What Are the Differences between CO2 Injection Offshore and Onshore?

CO2-EOR offshore, has the benefit of CO2 storage in addition to EOR. CO2 flooding in the offshore groups of reservoirs, will be different from the past experience of CO2 flooding onshore. Offshore developments are characterised by fewer wells, larger well spacing and higher rates per well. In this study, different aspects of CO2 flooding in these two groups of reservoirs are identified and compared, and possible opportunities for CO2 flooding offshore are identified.

To evaluate potential differences, CO2 flooding in a geological model was simulated under two different development scenarios (offshore vs onshore). Results show that both models are similarly affected by gravity. Offshore, because of larger inter well spacing, a greater degree of heterogeneity can be identified between well pairs. This makes the flow pattern more stable offshore which means that flow correcting mechanisms will be required to a lesser extent offshore.

The requirement for compression is also greater offshore. There are positive consequences for CO2 flooding offshore. The microscopic sweep efficiency increases due to higher miscibility development; the density difference between CO2 and other reservoir fluids decreases and net CO2 utilisation efficiency will be higher. This makes offshore reservoirs better candidates for coupled EOR and CCS CO2 flooding.