X-Ray tomography analysis of damage in synthetic polycrystalline rock salt: effect of confining pressure, brine and strain rate

Abstract:

To meet the objectives in terms of greenhouse gases emission, green hydrogen, produced from renewable energy sources, is becoming a promising energy carrier. Its massive storage is yet still a challenge to address.  Underground salt caverns have already been in use for seasonal storage of hydrocarbons. However, the intermittency of renewable energy sources means short-term storage with more frequent injection/withdrawal cycles. The tightness and integrity of the caverns under such loading conditions need to be ensured to successfully achieve the adaptation of the storage technique to hydrogen, used as an energy vector.

In previous works, the coexistence of intra-crystalline and inter-crystalline deformation mechanisms, such as grain boundary sliding have been highlighted by microscopy observations, essentially on the surface of dry synthetic polycrystalline salt samples tested under uniaxial loading conditions. It has also been shown that these mechanisms lead to micro-cracking of the material from the early stages of the plastic deformation.

The present work aims at extending these analyses to triaxial loading conditions, which are more representative of the operating conditions in salt cavern. It focuses on the evolution of porosity and micro-cracking inside the samples. In order to achieve this, 3D imaging using X-ray microcomputed tomography (XR-µCT) combined with in situ mechanical testing has been extensively used.

Synthetic samples have been prepared in both dry and humid conditions and tested under different confining and loading rates. In situ tests with XR-µCT observations have been performed at the laboratory tomograph and on the PSICHE beamline of synchrotron SOLEIL and have allowed us to investigate the effects of different loading conditions and the presence of brine on damage development.

Short bio:

Nina Du is a PhD candidate at Laboratoire de Mécanique des Solides, in collaboration with Laboratoire Navier, under the supervision of Alexandre Dimanov (LMS) and Michel Bornert. She graduated from Ecole Centrale de Nantes and is now working on rock salt for hydrogen storage in salt caverns. Her research focuses on the mechanical behaviour and micro-mechanisms in rock salt using triaxial tests combined with X-ray tomography observations.