Nanometer-Scale Deformations of Berea Sandstone under Moisture-Content Variations

Sandstone mechanical stability is of key concern in projects involving injections of CO2 in sandstone geological reservoirs, for the purpose of long-term storage. We develop a method to measure nanometer-scale deformations of sandstones in real time. We demonstrate that Berea sandstone, when hydrated, changes dimensions with a relative deformation of the order of 10-4. If the moisture content increases, sandstone samples exhibit an extension and if the moisture content decreases then the samples shrink. We also discover that, immediately after exposure to water, the sandstone temporarily shrinks, just for a few seconds, after which time a slow extension begins and continues until about half of the fluid evaporates. Such shrinkage followed by an extension is also observed when the sample is exposed to acetone, mineral spirits, or vacuum oil. The results are obtained using a high-resolution nanopositioner technique and, in independent experiments, confirmed using the technique of coda wave interferometry.