Skoltech researchers have found a way to produce hydrogen from natural gas with 45% efficiency right in the gas field by injecting steam and a catalyst into a well and adding oxygen to ignite the gas. Catalyst-assisted combustion produces a mixture of carbon monoxide and hydrogen, from which the latter can be easily extracted. This technology will help accelerate the transition from fossil fuels to clean hydrogen power. The study was published in Fuel.
Natural gas is also odorless and able to displace oxygen so I don’t see how it being CO2 underground instead of natural gas changes anything from a risk perspective. Maybe because the molecules are smaller and thus more prone to leaks? I’m admittedly way out of my depth here.
Methane is lighter than air and goes up while co2 is heavier than oxygen and stays down. I don’t know maybe in case of some disaster where water leaks in the well and then pushes out the co2
I wouldn’t want to live nearby in both cases anyway