Neutron imaging of coupled deformation and fluid flow in sandstones

X-ray tomography, in combination with Digital Volume Correlation (DVC), has been used in a number of recent geomechanics investigations to map the 3D heterogeneity of strain fields inside test samples, either during loading (“in-situ” tests performed with the loading device mounted within the imaging set-up) or with imaging before and after loading (pre-/post-mortem tests). In such studies, in-situ measurements have mostly been performed on sand and clays at low confining pressures. However, the poor penetration of x-rays through triaxial pressure cells capable of sustaining elevated fluid pressures limit the use of x-ray imaging for in-situ rock testing. This restriction is reduced by using neutron instead of x-ray imaging, as neutrons are more able to penetrate the metal confining vessels. Furthermore, the high sensitivity of neutrons to hydrogen makes them very useful to study water (or other hydrogen-rich fluid) related phenomena, which paves the way towards coupled deofrmation and fluid-flow studies.
In this work, the use of neutron imaging to measure deformation in sandstone samples and the resultant effect on fluid flow are explored using both pre-/post-mortem and in-situ testing. New results will be presented demonstrating the use of time-lapse neutron tomography in combination with DVC to provide 3D strain field mapping in deformed (pre-post-mortem imaging) and deforming (in-situ tests) sandstone specimens. Furthermore, analysis of fluid flow evolution through the same specimens will be presented. The coupling of the full-field deformation and flow mapping provide previously-inaccesible insight into how fluid-flow properties are changed in the regions where the most significant deformation is actually occuring, as opposed to measuring just bulk changes.