

You’re right about biofuel… Except that biofuel is already refined biomass. The water is already removed, usually to become as close to pure hydrocarbons as possible.
Hydrocarbons.
Chains of hydrogen and carbon.
Your comment demonstrates you’re not fully understanding the chemistry of the combustion. If you remove the “water” I am talking about, you wouldn’t have a hydrocarbon. You would have only carbon.
The “water” I am talking about is the “hydro” part of the “hydrocarbon”. That “hydro” does not become CO2 when it burns. That “hydro” becomes H2O.
When burning lighter hydrocarbons, the majority of the exhaust in the stack is actually water vapor rather than CO2. Putting that hydrogen into the ground, unburnt, provides no additional benefit over putting just the CO2 into the ground. It merely fills up the reservoir faster, and requires even more energy for the same amount of carbon sequestration. Burning that biomass, it is (theoretically) possible for the energy recovered (after powering sequestration operations) to be a net positive.
Sequestering the unburned biofuel without recovering that energy, the operation must be a net negative.




Volumetric efficiency is not the relevant metric. Energy efficiency is much more important. The process you describe requires far greater energy input to complete the sequestration.
Furthermore, the physical properties are a problem. Biomass appropriate to this process is conveyed as a flammable, pelletized solid; CO2 is an inert fluid. One of these can be pumped via pipeline into empty subterranean reservoirs; the other cannot.