Permanent carbon dioxide storage in deep-sea sediments

Abstract

Stabilizing the concentration of atmospheric CO 2 may require storing enormous quantities of captured anthropogenic CO 2 in near-permanent geologic reservoirs. Because of the subsurface temperature profile of terrestrial storage sites, CO 2 stored in these reservoirs is buoyant. As a result, a portion of the injected CO 2 can escape if the reservoir is not appropriately sealed. We show that injecting CO 2 into deep-sea sediments <3,000-m water depth and a few hundred meters of sediment provides permanent geologic storage even with large geomechanical perturbations. At the high pressures and low temperatures common in deep-sea sediments, CO 2 resides in its liquid phase and can be denser than the overlying pore fluid, causing the injected CO 2 to be gravitationally stable. Additionally, CO 2 hydrate formation will impede the flow of CO 2 (l) and serve as a second cap on the system. The evolution of the CO 2 plume is described qualitatively from the injection to the formation of CO 2 hydrates and finally to the dilution of the CO 2 (aq) solution by diffusion. If calcareous sediments are chosen, then the dissolution of carbonate host rock by the CO 2 (aq) solution will slightly increase porosity, which may cause large increases in permeability. Karst formation, however, is unlikely because total dissolution is limited to only a few percent of the rock volume. The total CO 2 storage capacity within the 200-mile economic zone of the U.S. coastline is enormous, capable of storing thousands of years of current U.S. CO 2 emissions.

Climate change and trace gases

“…Development of CO 2 capture at power plants, with below-ground CO 2 sequestration, may be a critical element. Injection of the CO 2 well beneath the ocean floor assures its stability (House et al 2006). If the power plant fuel is derived from biomass, such as cellulosic fibres 5 grown without excessive fertilization that produces N 2 O or other offsetting GHG emissions, it will provide continuing drawdown of atmospheric CO 2 .…”

Carbon Dioxide Capture and Storage

“…Concern over biological impacts and negative public opinion about ocean storage have curtailed interest and R&D in this area. 1 As an alternative to direct injection in the water column, a new approach to seabottom storage involving injection under the sea-bottom sediments that would overcome many of the concerns described here has been proposed, 10 although this option is in the early stages of R&D.…”

Carbon dioxide sequestration in deep-sea basalt

“…Important mechanisms for trapping CO 2 injected within deepsea basalt also include (i) blanketing deep-sea sediments, which form a low-permeability stratigraphic barrier impeding vertical fluid migration; (ii) the formation of CO 2 hydrate, which is denser and less soluble than liquid CO 2 in seawater Ͻ2°C (26); and (iii) gravitational trapping at water depths Ͼ2,700 m, where injected CO 2 is denser than typical seawater, causing it to sink (27)(28)(29). All three of these mechanisms are simultaneously available within ocean crust, providing independent protective barriers that could safely isolate the oceans, benthic ecosystems, and the atmosphere from leakage of CO 2 escaping from deepsea basalt aquifers.…”