Sediment routing controls on CO2 mineralisation potential

Geological storage of CO2 has the potential to decarbonise much energy production and heavy industry. The most secure mechanism for permanent trapping of CO2 is mineralisation.

Its effectiveness depends on: (1) the reactivity of mineral grains to injected CO2, and (2) rock texture, which controls dispersal of injected CO2 and the grain surface area available for mineralisation. Saline aquifers are the most attractive targets for storing injected CO2 at industrial scale, but many saline aquifers lack data required to characterise their mineralisation potential.

This project will use sediment routing concepts to develop a first-order predictive model of the mineralisation potential of sandstones, based on upstream-to-downstream trends in depositional grain size, sorting and mineralogical composition. These trends arise from selective deposition of coarse grain sizes and variations in the physico-chemical durability of different minerals during sediment transport. The grain sizes, sorting and mineralogy of sand

deposited in different segments of a sediment routing system are primary controls on the sandstone textures and geochemical characteristics that develop during burial diagenesis, and thus on their mineralisation potential. The project will focus on feldspathic sandstones, which contain calcium- and potassium-rich feldspars that react with and trap injected CO2 by precipitation of carbonate and clay minerals. However, feldspar grains also break down more

rapidly than quartz during transport - thus decreasing reactive mineral content and mineralisation potential.

1) The project will characterise trends in grain size, sorting and mineralogy in a modern sediment routing system draining the feldspar-rich, granitic and gneissic Iberian Massif, Spain.

The student will collect field data to develop a self-similarity-based depositional model for grain size, coupled to feldspar content evolution as a function of transport distance and climate.

2) The resulting model will be tested and calibrated against an ancient sediment routing system with CO2 storage potential. The feldspathic Sherwood Sandstone records deposition in fluvial, aeolian and lacustrine segments of the "Budleighensis" sediment routing system, which spanned the Wessex, Worcester, Cheshire, East Irish Sea, Solway and Carlisle basins, UK.

CO2 storage is planned or proposed in Sherwood Sandstone saline aquifers and/or depleted hydrocarbon reservoirs in these basins. Previous work implies that feldspar content in the sandstones decreases downsystem, from 20-50% in Wessex Basin to 5-8% in the Solway and Carlisle basins. The student will interpret seismic, well, core and outcrop data to document the sediment volumes, grain size characteristics and petrography of sandstones in the "Budleighensis" sediment routing system.

Results will have specific applications to CO2 storage projects in the UK, and also to generic assessment of CO2 mineralisation potential in sedimentary basins globally.