The presence of even a simple chemical reaction can delay or prevent the spreading of stored carbon dioxide in underground aquifers, new research from the University of Cambridge has revealed.

The
presence of even a simple chemical reaction can delay or prevent the
spreading of stored carbon dioxide in underground aquifers, new research
from the University of Cambridge has revealed.

                           

The
findings may have implications for carbon sequestration in saline
aquifers – one of the many methods being explored to mitigate rising CO₂
levels in the atmosphere.

Depending
on the strength of the reaction between dissolved CO₂ and porous rock,
the new research shows that distinct scenarios of CO₂ transport may
occur in deep saline rock formations.

Jeanne
Andres, a Schlumberger Foundation PhD researcher at the Department of
Chemical Engineering and Biotechnology at the University of Cambridge,
said: “If one knows the physical properties of the aquifer, one can now
calculate the movement of CO2 across it, and when it will begin to mix
with the brine. In theory, one can manipulate the strength of reactions,
thereby engineering the movement of CO₂ – keeping it in one area or
moving it to another within the aquifer – to enhance its storage
underground.”

With
weak reactions, the CO₂ will spread from the top throughout the depth
of the aquifer, but with stronger reactions, the CO₂ remains near the
top of the reservoir, leaving the deeper part inactive.

The
strength of these reactions can vary significantly among deep saline
reservoirs – rock formations possess a wide range of chemical reaction
rates depending on the mineralogy (e.g. calcite, dolomite, etc) as well
as other factors such as temperature and pressure. With the new
insight this research provides, it would now be feasible to consider
creating and injecting compounds which could alter the strength of
reactions in the aquifer.

To
arrive at their conclusions, the researchers established that the basic
interaction between fluid flow and the rate of chemical reactions
(chemical kinetics) in a deep porous medium is governed by a single
dimensionless number, which measures the rate of diffusion and reaction
compared to that of the natural mixing of fluids (convection).

As
applied to the storage of CO₂ underground, the scientists demonstrate
how this new parameter controls CO₂ flow and mixing in briny porous
rock. Through numerical simulations, the researchers found that above
this parameter’s critical value, reaction stabilizes the CO₂ system and
convection no longer occurs. Below the parameter’s critical value,
stronger reactions result in longer delays in the onset of convective
mixing throughout the reservoir.

For
systems with similar convective mixing strengths, stronger reactions,
indicated by rising values of the new parameter, can increase the
minimum rate at which pure, lighter CO₂ dissolves into the brine,
enhancing storage and reducing the risk of leakage.

Dr
Silvana Cardoso, Reader in the Department and project leader, said:
“This research shows how rigorous mathematical analysis coupled with
strong physical understanding can help us grasp the complex interactions
of flow and reaction in a carbon reservoir.  Such knowledge will be
valuable in guiding future approaches to carbon storage.”

The
paper ‘Onset of convection in a porous medium in the presence of
chemical reaction’ was published in the journal Physical Review E.

Study abstract

SOURCE