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Nanomechanics reveals the secrets of sedimentary rock

Porous sedimentary rocks make up a large part of Europe’s coastline and can be major oil reservoirs. However, little is known about their structure and properties at the nanoscale, even though these are linked to macro-scale behaviour.
Nanomechanics reveals the secrets of sedimentary rock
The TOMOTECH (Nanomechanics of natural materials from combining tomography and finite element modelling) project combined X-ray tomography and finite elements modelling (FE) on the nanoscale to predict the stability of chalk cliffs and the remaining oil in depleting reservoirs.

The Research Fellow selected two natural porous materials to test the validity of this approach. These were microstructured biological material in the form of the shell of the heart urchin and nanostructured geological material in the form of chalk.

Tomography was used to take 2D projections of the internal structure samples using X-rays. By rotating the sample and taking a large number of projections, it was possible to reconstruct the internal porosity of a sample in three dimensions. The 3D model was imported into finite element software and the stiffness was calculated for different parts of the heart urchin shell.

Chalk is a biogenic limestone formed from the remains of ancient algae and can serve as both an aquifer and hydrocarbon reservoir. Due to the small size of chalk grains a higher resolution was needed to investigate the sample, requiring the use of synchrotron X-ray tomography.

Mechanical simulations were carried out using the same approach as for the heart urchin, which revealed that chalk is much weaker than the heart urchin shell at the same porosity. Furthermore, its elastic properties drop rapidly with increasing porosity.

A technique known as dissipative particle dynamics (DPD) was also used to simulate the diffusion of particles in the nanoscale pore network of the chalk. This approach measured the tortuosity of the chalk samples, which showed how twisted the pore system was and was used to properly determine permeability.

Permeability is an important factor in the capability of a rock to promote fluid flow in oil production or groundwater flow. Results from the DPD simulations showed the chalk pores were very narrow, thereby significantly slowing down larger oil components. Moreover, the particles can become blocked at the surface.

TOMOMECH was successful in combining tomography and finite element simulations, thereby deriving the properties of materials. The results can be applied to coastal protection, the oil industry and biomimetic materials. It also provided important insights into the relationship between structure and function in biomineralised materials.

Related information


Sedimentary rock, TOMOTECH, nanomechanics, finite element modelling, X-ray tomography, chalk, heart urchin, aquifer, hydrocarbon reservoir, dissipative particle dynamics
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