Synchrotron 4D X-Ray Imaging Reveals Strain Localization at the Onset of System-Size Failure in Porous Reservoir Rocks

Abstract

Understanding the mechanisms of strain localization leading to brittle failure in reservoir rocks can shed light on geomechanical processes such as porosity and permeability evolution during rock deformation, induced seismicity, fracturing, and subsidence in geological reservoirs. We perform triaxial compression tests on three types of porous reservoir rocks to reveal the local deformation mechanisms that control system-size failure. We deformed cylindrical samples of Adamswiller sandstone (23% porosity), Bentheim sandstone (23% porosity), and Anstrude limestone (20% porosity), using an X-ray transparent triaxial deformation apparatus. This apparatus enables the acquisition of three-dimensional synchrotron X-ray images, under in situ stress conditions. Analysis of the tomograms provide 3D distributions of the microfractures and dilatant pores from which we calculated the evolving macroporosity. Digital volume correlation analysis reveals the dominant strain localization mechanisms by providing the incremental strain components of pairs of tomograms. In the three rock types, damage localized as a single shear band or by the formation of conjugate bands at failure. The porosity evolution closely matches the evolution of the incremental strain components of dilation, contraction, and shear. With increasing confinement, the dominant strain in the sandstones shifts from dilative strain (Bentheim sandstone) to contractive strain (Adamswiller sandstone). Our study also links the formation of compactive shear bands with porosity variations in Anstrude limestone, which is characterized by a complex pore geometry. Scanning electron microscopy images indicate that the microscale mechanisms guiding strain localization are pore collapse and grain crushing in sandstones, and pore collapse, pore-emanated fractures and cataclasis in limestones. Our dynamic X-ray microtomography data brings unique insights on the correlation between the evolutions of rock microstructure, porosity evolution, and macroscopic strain during the approach to brittle failure in reservoir rocks.

The Permeability of Porous Volcanic Rock Through the Brittle‐Ductile Transition

“…Indeed, the porosity of the samples deforming in the brittle regime decreased up to the peak stress (Figure 4b). These data are supported by recent image correlation analyses for volcanic rock deforming in the brittle regime, which showed evidence for the compaction of void space in off-fault volumes of the sample prior to the formation of the macroscopic shear fracture (McBeck et al, 2019; see also; Heap, Baud, et al, 2020; see also image correlation analysis for porous sedimentary rocks in the brittle regime by; Kandula et al, 2022).…”

Spatiotemporal evolution of seismicity during the cyclic operation of the Hutubi underground gas storage, Xinjiang, China

“…Both boundaries extended SW, in accordance with the extensions of the two clusters’ initiations. Strain localizations are believed to relate to small earthquakes 48 , 49 . Although we still lack enough information to carry out detailed 3-D modeling, we propose that the elastic and poroelastic stress changes together with injection induced strain localizations are responsible for the initiation of the two clusters during the capacity expansion stage.…”

Upgraded imaging capabilities at the BAMline (BESSY II)

“…Synchrotron X-ray imaging (SXI) is applied at synchrotron sources around the world in a broad range of scientific fields, such as materials science, biology, cultural heritage, geoscience and medicine (Arhatari et al, 2021;Olbinado et al, 2018;Schmelzle et al, 2021;Gao et al, 2021;Nogueira et al, 2017;Longo et al, 2007;Chen et al, 2020;Kandula et al, 2022;Rau et al, 2010). Relevant to BAM (Bundesanstalt fu ¨r Materialforschung und -Pru ¨fung) competencies, SXI proves suitable for nondestructive studies of materials and (small) components (Mayo et al, 2012;Heenan et al, 2019;Lin et al, 2017).…”