Greenpeace takes a hard line against CCS because they advocate for zero fossil fuels across the board, they don't want a solution that allows coal power plants or other fossil fuels to continue operating.
Because Greenpeace is adamently opposed to all fossil fuels, they are doubly opposed to using captured carbon for enhanced oil recovery. The whole idea is anathema to their philsophical approach and they hope it will not work and certainly work to convince the public that it cannot work, facts be damned.
Injecting CO2 into oil fields for EOR is a proven method to sequester CO2 permanently. 40 years of industry experience and extensive monitoring of the Weyburn field in Canada have proven that the CO2 will stay permanently sequestered. And it has been sufficiently demonstrated that there is potential for hundreds of gigatons to be sequestered in oil fields across the globe, and on top of that CO2 can be injected into shale, coalbeds and hydrate formations for enhanced gas recovery.
There are many sources of CO2 that can captured at much lower cost than from coal power plants, albeit at lower volumes. Ethanol distilleries, ethylene and hydrogen plants, oil refineries, natural gas cleanup, the list goes on.
The economics of carbon capture from coal are also greatly improved in polygeneration plants rather than straight power plants. Poygen plants that convert coal into synthetic liquid fuels or natural gas and chemicals already have the CO2 separation integrated into the process, and so the only additional costs are for the CO2 pressurization and pipelines. Biomass can also be blended with the coal in polygen plants greatly improving the overall carbon footprint.