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Offshore CO2 Storage in Continental Shelf Stratigraphy – Global Research Needs, Storage Potential, and Technical Challenges

Abstract

A successful strategy for matching anthropogenic CO2 sources with regionally extensive geologic sinks is to develop offshore storage sites beneath continental shelves. The strategy has been utilized for well-known and successful ongoing and planned projects in the North Sea; it is under consideration in Australia, China, Korea, Japan, United States, Brazil, Malaysia, and South Africa. Conditions favoring this strategy include: 1) high concentrations of CO2 sources near coasts and 2) accumulations of thick, geologically young, high capacity sediments of adjacent continental shelves. In such geologically young sediments 1) original porosity is likely preserved (high injectivity); 2) thick aerially extensive (transgressive) sealing intervals are still relatively ductile, (can self-heal), and 3) structural history is geologically brief, suggesting fewer or more predictable fractures and faults than older cratonic basins that may have experienced multiple episodes of deformation. Global reconnaissance evaluation of continental shelves shows extensive potential in many other areas (e.g., Africa, India, South America, and Southeast Asia). Identification and quantification of CO2 storage resources in continental shelf settings is needed because in many regions the flat and arable land typical of onshore sedimentary basins hosts dense populations, elevating risk and decreasing public acceptance of geologic storage. These same areas are where current and developing CO2 sources are located. CO2 storage potential is related to geologic setting and basin evolution and therefore can be broadly compared globally. Continental shelf sediments typically form progradational wedges, often with thick, sand-rich accumulations associated with continental drainage fluvial systems (e.g. Congo, Rhine-Meuse, Mississippi, Indus, Ganges-Brahmaputra, etc.). In low latitudes, shelves comprising carbonate ramps, shelves, and reef complexes present diverse storage opportunities but have received little attention for CCS to date. Technical issues that are the focus of ongoing research with respect to CCS include 1) the variability/similarity of continental shelf geologic settings globally with respect to storage capacity assessment, infrastructure development and monitoring; and 2) how readily knowledge gained in one area (e.g., the North Sea) can be applied globally. Reconnaissance evaluations of global storage potential in continental shelves and options for next steps will be discussed.