1. Liquid CO2 would carry sand just as easily as any other liquid.
2. CO2 can’t contaminate groundwater.
3. CO2 can be easily separated from the nat gas and reused.
4. Process would use far less water and produce far less liquid waste.
You may want to learn a little more about C02 and the temperature/pressure required to stay at a liquid.
Sending freezing liquid, even if you could keep it from solidifying, into a Petroleum reservoir would thicken the hydrocarbons limiting the flow of the CO2. If you do start at a liquid phase on the ground, the initial cracking would enlarge the volume, creating pressure drop and solidifying the CO2 stopping the growth of the cracks, which is the whole point of fracturing process. Water is used for this method because of the very low compressible property of the fluid.
2. CO2 can’t contaminate groundwater.
Neither does hydraulic fracturing. The contamination cases have all been linked to casing failures. Those would result in contamination regardless of fracturing methods.
3. CO2 can be easily separated from the nat gas and reused.
There is significant expense in doing so. I've been part of the design team for such facilities. And you have accomplished nothing to appease the global warming crowd as you have not sequestered the CO2.
4. Process would use far less water and produce far less liquid waste.
Since item one makes it all unworkable, that is a mute point. And also your claimed method only uses a more difficult fluid to handle and maintain, the problem is more complicated.