FLUIDS AND ENVIRONMENT GROUP

Our advances in predicting the behaviour of the plumes of greenhouse gases CO2 and methane has the potential to limit their environmental damage.

The challengeGreenhouse gases, whether man-made or natural, are a huge threat to the planet. If their behaviour can be predicted it will be possible to limit the damage they cause.

Our world-leading research focuses on the behaviour of fluid buoyant plumes and flow in porous rocks. In the field of CO2 storage we wanted to find out if assumptions that dissolved CO2 sinks and therefore becomes safer were correct.

We also wanted to be able to predict the behaviour of methane plumes and to extend this research to industrial chemcial clouds. Methane is continuously released from the seabed in giant plumes; this process can become unstable when the temperature of seawater rises. An unstable release of methane could cause an environmental catastrophe.

Our work in tackling thisUsing ground-breaking laboratory analogues, we focus on describing the interaction of fluid dynamics and reactions in the following two key areas.

Carbon: we study the behaviour of dissolved CO2 and have made a crucial discovery about how reactions affect it spreading when it is stored underground. Carbon capture and storage (CCS) limits large quantities of CO2 from entering the atmosphere by capturing it as it is released by large fossil fuel power plants. It had been assumed that captured CO2, once dissolved, becomes denser and is carried deeper into aquifers and underwater pools by convection currents.

Deeper means less: graph shows the spreading of CO2 when stored in a saline reservoir. The coloured lines show how the concentration of dissolved CO2 diminishes with depth. Different reaction strengths are measured as Da/Ra2.

We have discovered that if dissolved CO2 is surrounded by silica-rich rocks, a reaction takes place that may shut off convection within as little as two months. This means that stored CO2 may remain in shallower regions for possibly thousands of years, while deeper areas may stay carbon-free.

Methane: it is estimated that 6,000 gigatonnes of this greenhouse gas are held in the sediment of the world’s deep and cold oceans. Mud volcanoes deep in the seabed constantly release some of this methane, which rises, either dissolved in seawater or as gas bubbles. Our research into hydrate-formation reactions focusses on how methane plumes may become unstable with very slight rises in temperature.

MethodologyWe combine modern mathematical techniques, computational modelling and lab experiments: advanced Hele-Shaw cells to mimic flow in porous rock and provide an analogue for the movement of dissolved CO2 in brine; density meters for direct sampling, which provide information on the width of the buoyancy field and its spatial variation within the plume or cloud; and particle image velocimetry (PIV) and colourimetry to provide instantaneous velocity and concentration fields

Potential applications we are working on1. Predicting the behaviour of buoyant plumes and clouds

We have also studied the spreading dynamics of chemical plumes, including leakages and explosions in the chemical industry, eg the nuclear cloud released at Fukushima Daiichi nuclear plant in Japan and the BP oil plume in the Gulf of Mexico.

2. Carbon storage Our research into the chemical reaction between stored CO2 and

the host rock in an aquifer will enhance the safety of CCS.

Our techniques and skills• In the laboratory: PIV; infra-red spectroscopy; spectrophotometry;

colourimetry; densitometry; laser-induced fluorescence imaging.• Analytical mathematical techniques: scaling; perturbation methods;

asymptotics; stability analysis.• Computational research: state-of-the-art partial differential equation

(PDE) solvers such as FastFlo, Mathematica, MatLab.

What is new about our work? We are the first team in the world to study the behaviour of dissolved CO2 underground and under the sea.

Industrial partnerships and future applicationsOur research is of global significance and we are currently seeking industrial partnerships.

Dr Silvana Cardoso, University of Cambridge, Department of Chemical Engineering and Biotechnology, Pembroke Street, Cambridge, CB2 3RA Tel: 0044 1223 331863 Email: sssc1@cam.ac.uk Web: www.ceb.cam.ac.uk/research/groups/rg-feg

The team

FLUIDS AND ENVIRONMENT GROUP continued

Shut off: laboratory experiments demonstrating the shut off of convection by chemical reaction. This sequence of photographs shows the behaviour of CO2 (pink) in brine (yellow) in a Hele-Shaw cell with a fluid-fluid interface. The speed of the reaction (Da/Ra2) affects the motion of the CO2 through the brine.

Oceanic bubbly plumes: PIV showing how a plume of CO2 bubbles or droplets rises in the deep ocean. Colour indicates the scattering of light and the speed of the chemical reaction inside the plume.

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