Safe storage and effective monitoring of CO 2 in depleted gas fields

Carbon capture and storage (CCS) is vital to reduce CO 2 emissions to the atmosphere, potentially providing 20% of the needed reductions in global emissions. Research and demonstration projects are important to increase scientific understanding of CCS, and making processes and results widely available helps to reduce public concerns, which may otherwise block this technology. The Otway Project has provided verification of the underlying science of CO 2 storage in a depleted gas field, and shows that the support of all stakeholders can be earned and retained. Quantitative verification of long-term storage has been demonstrated. A direct measurement of storage efficiency has been made, confirming that CO 2 storage in depleted gas fields can be safe and effective, and that these structures could store globally significant amounts of CO 2 . Recent public opposition has caused setbacks to high-profile onshore CCS projects in Europe, such as Shell’s Barendrecht project, and Vatenfell’s in the Altmark. However, the Otway Project demonstrates that this opposition is not inevitable. As a range of our results are published, they reemphasize that geological carbon storage is sufficiently well-understood, scientifically and technically, to be scaled up to its key role in combating global warming. It is particularly important to have demonstrated that monitoring techniques are practical and quantitatively adequate to ensure safety, protect financial and physical assets, and guarantee climate abatement. No single project can answer all questions or remove all doubts, but our measurement of capacity is an empirical finding that shows previous estimates to be well-founded: There is large, useful capacity, worldwide, in depleted gas reservoirs. Obstacles to using this capacity are more social and political than scientific or technical. It is important to know the capacity of subsurface storage for CO 2 . The global volumetric pore space is large, but the realistic storage capacity is diminished by many practical factors such as depth, the presence of suitable sealing rocks, or distance from sources. In the case of depleted gas fields, an important factor is the ability of injected CO 2 to reoccupy the pore space formerly containing natural gas. The potential capacity in depleted gas fields has been estimated to be significant on a global scale ( 5 ). By monitoring the rate of filling as we injected CO 2 into the Naylor field, we made an initial direct measurement of this i