depth matters sure..... but only the seal on the top enables the sequestration. this means that the gas caverns will need to be managed in the same manner as a nuclear waste dump..... for hundreds upon hundreds of years. seals don't last forever.
this is the key fault in the reasoning around CCS and why it is a fail-doomed technology..... no company has yet been able to make CCS a sustainable proposition either economically or environmentally.
