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Optimization Under Uncertainties for CO₂ Sequestration in Deepwater Sediments

CO₂ injection and storage in deepwater sediments under water depths greater than 9,000 feet 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 Japan, the East coast of China, the South-west and East coasts of the U.S. 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 (central Pacific, Japan Sea, and Gulf of Mexico). Since not all regions and sediments deposited below 9,000 feet of ocean waters are appropriate for CO₂ storage, 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 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. 1000 years) are used to assess the effect of different decision and uncertain variables on the behavior and the evolution of the CO₂ plume within the sediments. Also, response surface and Monte Carlo methodologies have been used to quantify the risk associated with each of the critical parameter 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 mapping of the world’s oceans and deep seas best candidates for CO₂ storage in deepwater sediments.

AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California