A model suggests that CO2 sequestration in seabed sediments could be a viable option

A pair of researchers from Peking University found evidence that suggests liquid CO2 could be sequestered safely in deep marine sediments. In their article published on the site of free access Science Advances Yihua Teng and Zhang Dongxiao describe a model that they have built to mimic CO2 injections under the sea floor and what 39, he showed.

As the planet continues to heat up because of the continuing release of greenhouse gases into the atmosphere, scientists are looking for other places to store them. Carbon dioxide has been designated as one of the main greenhouse gases and as a result, efforts have been made to curb its release. Some approaches have focused on finding ways to prevent spread, while others are looking for ways to capture and store the product where it will not end up in the atmosphere. Such a place is in the sediments that lie at the bottom of the ocean. But, as noted by the authors, little work has been done to find out if such a site could contain CO2 without leakage into the water – and possibly into the atmosphere. In this new effort, researchers constructed a model to mimic ocean bottom sediment conditions and what could happen if liquid CO2 was injected into it.

Coal-fired power plants are one of the main contributors to the release of CO2 into the atmosphere. . Work is under way to find ways to sequester CO2 in these emissions. Such work has shown that CO2 can be captured and converted into various forms, from solids to liquids. This is the liquid form that researchers with this new effort address.

Previous research has shown that when liquid CO2 is exposed to both high pressure and low temperatures, hydrates form. The researchers added this information to their model and then performed it several times under different conditions, such as varying pressure and time scales. They found that under certain conditions, the injection of CO2 into the sediment led to the formation of hydrates, which then served as plugs, preventing the CO2 liquid from seeping upwards. They also found that over time, CO2 and hydrates dissolve in the interstitial fluids.

Emboldened by their findings, the researchers suggest actual studies on CO2 sequestration in seabed sediments to determine whether there is a viable solution.

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More information:
Yihua Teng et al. Long-term viability of carbon sequestration in deep sediments, Science Advances (2018). DOI: 10.1126 / sciadv.aao6588

Abstract

The sequestration of carbon dioxide in deep sediments has been proposed for the long-term storage of anthropogenic CO2 that can take advantage of the offshore infrastructure current. It benefits from the negative buoyancy effect and the formation of hydrates under conditions of high pressure and low temperature. However, the multiphysical process of CO2 injection and post-injection and the feasibility of subsequent CO2 removal under different geological and operational conditions have not been well studied. With a detailed study of coupled processes, we investigate whether CO2 storage in seabed sediments is viable, effective and safe in the long term. We are also studying the evolution of multiphase and multicomponent flow and the impact of hydrate formation on the efficiency of storage. The results show that the low buoyancy and high viscosity slow down the rising plume and that hydrate cap formation effectively reduces permeability and eventually becomes an impermeable seal, thus limiting the movement of CO2 to the seafloor. We identify different models of flow at various time scales by badyzing the mbad distribution of CO2 in different phases over time. We observe the formation of a fluid inclusion, consisting mainly of liquid CO2 and encapsulated by a diffusion – dominated impermeable hydrate film. The trapped liquid CO2 and the CO2 hydrate eventually dissolve in the interstitial water by diffusion of the CO2 component, resulting in permanent storage. We perform sensitivity badyzes on storage efficiency under varying geological and operational conditions. We find that in an offshore environment, CO2 sequestration in intact marine sediments is generally safe and permanent.