Carbon sequestration doesn't necessarily mean driving combustion in reverse to get oxygen and hydrocarbons again. Accelerated silicate weathering could remove a lot more atmospheric CO2 per unit of energy invested and it generates carbonate minerals rather than fuel that people would be tempted to burn again. Like this, "Enhanced weathering strategies for stabilizing climate and averting ocean acidification": http://www.southampton.ac.uk/assets/imported/transforms/cont...