Passing Gas: Policy Implications of Leakage From Geologic Carbon Storage Sites

Publisher Summary Increasing attention is being given to injection of carbon dioxide (CO2) into geologic reservoirs as a management technique to reduce releases of greenhouse gases (GHG) to the atmosphere. Among the many issues that need to be resolved for geologic carbon storage to be an effective GHG management technique is the leak-rate performance of the system. Storage sites must be designed to avoid sudden releases, which could pose acute risks of asphyxiation. The more complex challenge is to structure a design strategy and oversight system that not only has the goal of limiting slow leaks to the atmosphere to a de minimis level but also is robust if we, or future generations, encounter less than perfect performance in real-world operation. To be effective as a carbon mitigation strategy, geologic storage systems must not leak more than trivial amounts over time spans of hundreds of years. While individual sites can have varying slow leak rates without undermining effectiveness, the system as a whole must be close to leak-free. One might think at first blush that the choice of a stabilization target for GHG would be the strongest driver of the maximum permissible long-term leak-rate from the storage system. However, annual global GHG budgets for stabilization targets between 450 and 750 ppm tend to converge at low levels within two to three hundred years. This means the cumulative amount of carbon stored during this period has a major influence on the required performance of the storage system, regardless of the stabilization target selected.