New Insights Brought by Micro-Tomography to Better Understand Gas Transfer Property Variation and Coupling Effects in Salt Rocks

In the context of salt cavern applications, this experimental study is dedicated to the characterization of fluid transfer and poromechanical properties of salt rock under isotropic and/or deviatoric stresses. Triaxial test was used to investigate permeability variation with deviatoric stress and time, and simultaneously to get damaged sample. Uniaxial test was also performed as it is more likely to produce damaged sample with cracks, thus highlighting the crucial role of cracking on permeability and couplings. Those pre-damaged samples were then tested again under hydrostatic loading to investigate damage effects and potential sealing/healing. Meanwhile, X-ray micro-tomography experiments were performed to evaluate the internal microstructural changes due to mechanical loadings. They revealed to be consistent with both the permeability evolution and the coupling effect intensity, which is characterized by Biot’s coefficient measurements. The damaged samples were found to have higher permeability and more significant coupling effects due to cracking. The results also support the hypothesis that fluid flows through cracks or grain joints and that couplings are mainly due to fluid pressure effect into those cracks. Time effects on permeability were detected for both hydrostatic and triaxial tests.