Speaker
Dr
Stephen Hall
(ESS / Lund University)
Description
Understanding the mechanisms of deformation and failure in rocks and their implications for fluid-flow and -storage are key to a number of important industrial/environmental applications, including geologic CO$_2$ sequestration and hydrocarbon production. The common method to analyse the deformation behaviour of rocks is triaxial compression testing where an axial load is applied to a sample under some confining pressure, which aims to simulate subsurface conditions. In such tests, stress and strain are measured at the boundaries of the sample and fluid flow can be measured by monitoring flow rates or fluid pressures at the ends of the test specimen. The standard interpretation of such data requires assumptions of homogeneity of the samples and the properties being measured/inferred. Unfortunately, this assumption is very rarely valid, as rocks are generally heterogeneous and failure occurs through some localised phenomena, such as strain localisation or fracture, which implies heterogeneity of stresses, strains and fluid flow. Therefore experimental techniques that permit full-sample observation of the deformation and flow are required.
This presentation will cover recent progress in using neutron diffraction and imaging (radiography and tomography) with in-situ experiments to characterise deformation mechanisms in rocks at different scales as well as to investigate the coupling between mechanical deformation and the evolution of the hydraulic properties of rocks. The reasons for using neutrons for these studies are two-fold: (i) neutrons can penetrate the metals used in pressure containment vessels, so enable “in-situ” measurements of samples under pertinent confining pressures (10’s MPa); (ii) sensitivity to hydrogen, which provides a highly sensitive measurement of water distributions and movements in bulk rock samples plus the possibility to exploit H$_2$O/D$_2$O contrast. Scanning neutron diffraction is used to map strains in the crystalline rock grains, which can potentially provide information on force/stress heterogeneity. A new experimental set-up and recent results from this work will be presented. In another project, neutron imaging is used to follow the 3D structural evolution of samples undergoing deformation, in-situ in the imaging set-up. 4D image analysis enables the deformation field and evolving heterogeneity to be characterized from the time-lapse images. This deformation analysis is linked to imaging of fluid flow through the samples at different stages of deformation with the ultimate aim to characterise the coupled hydro-mechanical processes
Primary author
Dr
Stephen Hall
(ESS / Lund University)
Co-authors
Dr
Erika Tudisco
(Lund University)
Ms
Maddi Etxegarai
(University of Grenoble)
Mr
stefanos athanasopoulos
(Lund University)
