Exploring carbon storage deep beneath the seabed

Date:
December 2, 2021
Source:
University of Bath
Summary:
A new study sheds light on the way salty water acts in deep-sea
aquifers, paving the way for further research into carbon storage
deep beneath the seabed.



FULL STORY ========================================================================== Pools of salty water (brine) trapped beneath the seabed offer an
unparalleled opportunity to sequester carbon and keep it trapped for
millennia. Yet research in this area remains rudimentary, as little is
known about the way sodium chloride (salt) behaves when it's combined
with carbon dioxide several kilometres beneath the surface of the earth,
where conditions of heat and pressure are extreme.


==========================================================================
Now a study from the University of Bath is shedding new light on the way
saline solutions act in deep geological formations (known as aquifers),
paving the way for further research into CO₂ sequestration beneath
the seabed. The final aim of this work is for pipes to carry CO₂
from the earth's atmosphere into these aquifers, where it will be stored harmlessly, potentially forever.

Working out how CO₂-laden salty water behaves under extreme
conditions in the presence of rock is important. Will it dissolve in
the water and react with the rock, or will it simply bubble back to
the surface at the first opportunity, like the bubbles from a bottle
of cola after it has been shaken and opened? In an ideal world, the combination of seawater and CO₂ under pressure will result in the formation of rock, though it is more likely that the blend will retain
its liquid form. "Providing the rock above the solution is fault- free
and impermeable, the CO₂ will stay there," said co-author Professor Philip Salmon, from the Department of Physics.

For the study, published in the Journal of Chemical Physics, the
researchers observed saline solutions under conditions of pressure and temperatures that mimic the conditions found in deep aquifers. Their
'neutron diffraction' technique allowed them to examine saline solutions
in more extreme conditions than ever before. Using this technique, they
studied different isotopes (or versions) of sodium chloride, allowing
new insight into the way salty water behaves under different sets of
pressure and temperature conditions.

The chemistry of salty solutions mixed with CO₂ Little is known
about the chemistry of mixing saline solution and CO₂ at high
pressures and temperatures. Previous experimental efforts to find answers
have failed because the solution, under extreme conditions, is highly
corrosive and destroys the lab equipment it's contained within before
results are yielded.

"Being able to hold these solutions without the apparatus falling to
pieces was a big challenge," said co-author Dr Anita Zeidler, also
from the Department of Physics. "We overcame them through the design of high-pressure apparatus and a judicious choice of containment materials." Describing the research, Professor Salmon said: "Our experiments show
that by using neutron diffraction, you can see how the salt ions and
water molecules interact under quite extreme conditions of heat and
pressure. Next, we'll be attempting to dissolve carbon dioxide into the
saline solutions. The results from these experiments will inform models on carbon sequestration mechanisms, with the end-goal being to find a way to safely sequester carbon dioxide in deep-sea aquifers." The sequestration
of CO₂ in deep aquifers is one of the global strategies being
explored for carbon capture and storage. Pilot plants have demonstrated
the success of this strategy, but ramping-up the scale depends on solving
some key issues, such as storage capacity. It's therefore important for scientists to improve their knowledge of the physics and chemistry of
CO₂ in the environment into which it is injected.

The researchers hope to find collaborators with an expertise in
corrosion and corrosion resistance before they start the next phase
of their project. "We want to study saline solutions under even more
extreme conditions that fully fit in with real-life conditions, and these conditions will be even more corrosive. So, we could really benefit from
the input of a corrosion specialist," said Dr Zeidler.

This work was led from Bath and benefitted from the significant
contributions of two PhD students, Annalisa Polidori and Ruth
Rowlands. Also collaborating were researchers from three institutions
in France: Sorbonne Universite', Universite' Paris-Saclay and Institut Laue-Langevin in Grenoble.

========================================================================== Story Source: Materials provided by University_of_Bath. Note: Content
may be edited for style and length.


========================================================================== Journal Reference:
1. Annalisa Polidori, Ruth F. Rowlands, Anita Zeidler, Mathieu Salanne,
Henry E. Fischer, Burkhard Annigho"fer, Stefan Klotz, Philip
S. Salmon.

Structure and dynamics of aqueous NaCl solutions at high
temperatures and pressures. The Journal of Chemical Physics, 2021;
155 (19): 194506 DOI: 10.1063/5.0067166 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/12/211202141517.htm

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