CO2 injection and storage in deepwater sediments under water depths greater than 9,000 feet (˜2,750 meters) where high pressures and low temperatures result in the CO2 being denser than seawater and therefore being buoyantly trapped in the sediments pore-fluid, could provide an attractive sequestration option for countries and regions densely populated and emitting large quantities of anthropogenic CO2 such as East and West Coasts of the United States of America, Japan, the East Coast of China and Western Europe. In these places, public opinion, government regulatory agencies, a lack of space for CO2 injection sites and few depleted oil and gas fields available necessitate the application of alternative technologies to sequester CO2 in order to mitigate a significant part of the 30 billion tons of CO2 annually released in the Earth's atmosphere.

This paper presents the results of multiple reservoir simulations and parametric studies for different types of deepwater sediments located in various regions of the globe (Pacific Ocean, Atlantic Ocean, Japan Sea and Gulf of Mexico). Since not all regions and sediments deposited below 9,000 feet of ocean waters seem to be viable to permanently store CO2, this study focuses on the critical parameters that need to be considered to successfully inject and permanently store liquid CO2 in deepwater sub-seabed sediments.

In fact, when injecting liquid CO2 through an ultra-deepwater conduit (injection pressurized riser) within the first few hundreds of sediments, several uncertain variables such as temperature, sediment type, sediment thickness, permeability, porosity and CO2 injectability greatly influence the overall integrity of the buoyant trap. Very long-time reservoir simulations (e.g. 250 years) have been used to assess the effects of different decision and uncertain variables on the behavior and the evolution of the CO2 plume within the sediments. Also, experimental design and response surface methodologies have been used to quantify the risk associated with each of the critical parameters and to determine the optimal conditions for deepwater sediments CO2 storage. Finally, the essential findings of the paper provide the offshore and carbon sequestration industries with a high-level mapping of the world's oceans and deep seas best candidates for CO2 storage in deepwater sediments.

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