CO₂ Sequestration Studies in Ocean and Deep Sea Sub-seabed Formations

Because supercritical CO₂, when injected onshore or in shallow water depths offshore, is mobile and can, therefore, migrate through any conduits or fractures, there is a need for proper physical trapping and also a necessity to monitor the CO₂ migration in the injected zone. In addition, public opinion, government regulatory agencies and the lack of space for CO₂ injection sites in some of the largest CO₂ emitting regions of the world encourage investigating other alternatives such as CO₂ sequestration in deepwater sub-seabed formations.

Indeed, at the high pressures and low temperatures reigning in deepwater sediments where water depths are greater than 9,000 feet, scientists have suggested that the CO₂ should become denser than seawater and therefore would remain buoyantly trapped when liquid CO₂ is injected within the first few hundred feet of sediments even in the absence of geological seals and traps. Furthermore, the bulk of the studies and technical papers concerning CO₂ sequestration in deepwater sediments have focused on showing the potential and the feasibility of the concept but very little has been published to demonstrate the viability of the injection and long-term storage of CO₂ in deepwater sub-seabed formations.

This paper presents the results of several case studies located in the Sea of Japan, the Gulf of Mexico, the Pacific Ocean and the North Atlantic Ocean. Large time-scale reservoir simulations have been conducted for up to 1000 years and show that injected liquid CO₂ can remain trapped in deepwater sediments. In addition, the different case studies and numerous simulations show evidences that not all regions and sediment deposited below 9,000 feet of ocean waters are appropriate for CO₂ storage. Therefore, CO₂ sequestration in deepwater sediments provide another attractive technical solution when applied under certain conditions of pressure, temperature, sediment type, thickness, permeability and porosity notably for regions where there are few depleted oil and gas fields available for storage or limited space accessible onshore.

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