Coupling Digital Image Correlation and Fourier Transform Infrared Spectroscopy for Identification and Characterization of Swelling Regions in Heterogeneous Shales

Abstract The swelling behavior of shales plays a pivotal role in the development of unconventional reservoirs. This phenomenon is greatly influenced by the mineral composition and variability within shale formations, which, in turn, govern the intricate response of shale to aqueous solutions. Existing methods for assessing the mineralogical attributes of shale and shale's mechanical response to surrounding fluids fall short of providing a comprehensive analysis of intact samples while preserving their inherent in-situ heterogeneity. In response to these limitations, this study introduces an innovative methodology for identifying and characterizing shale regions prone to swelling by coupling the Digital Image Correlation (DIC) non-contact optical technique with micro-Fourier Transform Infrared Spectroscopy (micro-FTIR) mineral mapping. The DIC method was employed to dynamically measure and visualize the spatially resolved complex tensile strain development in shale as it interacts with water-based fluids. The micro-FTIR technique was used to generate a full-field map of the in-situ formed mineral distribution within the regions of interest on the shale surface in the direction parallel to bedding. As the results of the micro-FTIR correlation to the spatial tensile strain maps acquired from the DIC, it was found that the most affected regions in the Eagle Ford (EF) and Tuscaloosa Marine Shale (TMS) are the clay-rich zones. Additionally, areas with a prominent presence of aliphatic hydrocarbons exhibited lateral deformation upon contact with water-based fluids. The analysis of swelling anisotropy in both unconventional formations revealed a significant predominance of transverse expansion, whereas the potential of salt to yield an isotropic response of EF shale was uncovered.