Geological storage of carbon dioxide in oceanic crust

Abstract

The rise of atmospheric carbon dioxide (CO2), due to decades of burning of fossil fuels, is a key driver of anthropogenic climate change. Carbon Capture and Storage (CCS) is one of the most promising mitigation strategies for long-term sequestration of CO2.
Unlike most conventional CCS investigations targeting deep saline aquifers, this thesis focuses on the potential of the uppermost oceanic crust, inspired by the strong evidence that basaltic seafloor has acted, in the past, as a major sink for CO2.
The study of temperature, pressure, and density of CO2 and seawater at the sediment-basement interface for the whole seafloor highlights the influence of water depth, sediment thickness, and oceanic crustal age on the relative gravitational stability of CO2. Consequently, 8% of the entire oceanic crust is recognised as suitable for gravitational and physical trapping of CO2 injected into the basement. Five potential targets are proposed, and even the smallest of these provides sufficient carbon dioxide sequestration capacity for the next centuries.
Batch experiments on the mineral dissolution of submarine mafic rocks and ophiolitic gabbro, in CO2-rich solutions, contribute to improve the fundamental understanding of geochemical reactions at mid-ocean ridge flank temperatures (40 ?C). Concentrations of silicon and calcium in solution, and particle size are identified as the key factors to quantify the rock reactivity. Ca dissolution rates suggest calcite, plagioclase and amphibole are the principal sources of calcium at pH ~5.
The attempted estimation of costs related to the transport and storage of 20 Mt/yr of CO2 in deep-sea basalts, as a function of distance from the shore, injection rate, and water depth, shows the economic feasibility of potential offshore CCS projects. Overall, the expenditures are dominated by the number of ships and wells required to deliver large volumes of CO2 to reservoirs located far from the coast, rather than by the water depth. These financial considerations could potentially improve if the CCS strategies conquered a significant place in the global market.

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ORCID for Damon Teagle: orcid.org/0000-0002-4416-8409

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