Well, only if the patent-holder makes no effort to maximize the return on its investment in those 20 years. But if the technology is really that effective and the patent-holder is even a little bit economically rational, then presumably the patent holder will be the one pushing hardest to make this the standard thing to do with recovered CO2 well before the patent expires.
Not that patents are all roses and puppy dogs. But this is too big a part of the picture to just ignore.