Measurement of Deformation Heterogeneity during Shale Swelling using Digital Image Correlation

Rock-fluid interactions in shale formations is one of the main sources of wellbore instability issues, inadequate stimulation performance or the sealing efficiency of shales for carbon dioxide storage in subsurface formations. For better planning of these operations, it is important to understand the mechanisms behind these interactions. These issues are especially prevalent in clay-rich shales. Conventional techniques to quantify these shale-fluid interactions comprise of measuring swelling in powdered rock grains or measurement of deformation in the whole pieces of core using LVDT and strain gages. However, the contribution from individual laminae to overall deformation cannot be evaluated using these classical methods. In this study, we developed an experimental setup to evaluate the spatial deformation in shale during interaction with water using digital image correlation (DIC). Deformation of two shale samples, with 34 wt% to 51 wt% clay content, were studied. White paint was used to generate a random speckle pattern on the specimen and then immersed in deionized water. The deformation process was captured using a digital camera and images were analyzed using DIC to quantify the deformation. The implementation of the DIC technique enables the visualization and quantification of spatial deformation in the specimen during interacting with water. The results show localization of large strains in select laminations. The results provide a better understanding of shale deformation when interacting with water in comparison to traditional measurements that can provide only an average strain value.