Sandstone formations often hold vast stores of hydrocarbons or are viable candidates for sequestering large volumes of CO₂. The ability of a particular sandstone to support hydrocarbon extraction or carbon storage is related to its porosity, permeability, and changes in these properties due to deformation. Traditional methods of investigating sandstone properties rely on examining two-dimensional slices of extracted samples. However, much information about sandstone structure and mechanical behavior is simply inaccessible using the thin-sectioning approach. 

Now for the first time scientists have used three complimentary X-ray methods to investigate a sandstone sample under compression. The sample consisted of Nugget sandstone, prevalent in the American West and characteristic of low-porosity sandstones found elsewhere. Three-dimensional imaging of the sample was performed at beamline 1-ID-E of the Advanced Photon Source, a U.S. Department of Energy (DOE) Office of Science user facility at DOE’s Argonne National Laboratory. Researchers made use of X‐ray computed tomography (XRCT), along with far-field and near-field high‐energy diffraction microscopy (ff-HEDM and nf-HEDM). 

The results provide new insights into sandstone properties under compression. For instance, sandstone grains featured cements on their surfaces that reduced porosity and responded to induced stresses similarly to the grains in non‐cohesive materials. This study highlights the efficacy of using these complimentary 3D imaging techniques to study bulk sandstone under compression, which helps characterize its potential as a storage site for CO₂.

Sandstone is a polycrystalline rock, composed of sand grains locked together. During formation, sand grains are cemented together through dissolution and precipitation of silica or other minerals. Sandstones are riddled with voids, making them porous and allowing fluids to flow through them. The ease with which fluids can flow through a sandstone is indicated by its permeability, which is related to but distinct from porosity.

Nugget sandstone originated from wind-blown sand and is prevalent in the American West. The grains and cements in Nugget sandstone are heterogeneous, and the rocks feature porosities from one to twenty-five percent. This study utilized Nugget sandstone from Colorado, composed of roughly 90 percent quartz, 10 percent finely-textured clay kaolinite, and trace amounts of other clays.

Measuring slightly under one cubic millimeter, the tiny sample nevertheless allowed measurements of crystal orientations, structure, and stresses in hundreds of grains in 3D, something unobtainable using conventional 2D-sectioning techniques. A monochromatic X-ray beam, shaded yellow, was focused on the sandstone sample, which was slowly compressed in steps using an in-grip deformation device known as the Rotational and Axial Motion System 3 (RAMS3). Note that the XRCT and nf-HEDM detectors are close to the sample, while the ff- HEDM detector is much further away (about 1.6 meters).

Near-field HEDM was used to map the lattice orientations of individual grains in 21 distinct layers within the sample prior to compression. The use of specialized software was essential for discerning one grain from another based upon the nf-HEDM data. Crystalline misorientation, meaning the divergence in crystallographic orientation within individual sand grains, was determined to be greater for larger grains.

XRCT data was collected following each compression step. Fig. 1A shows one XRCT slice through the sample, corresponding to Layer 1 from the nf-HEDM imaging. Fig. 1B shows Layer 1 following “watershed segmentation”, a technique that isolates individual pores and grains. Fig. 1C shows the entire sample captured by XRCT.

The stress evolution of the sandstone sample following repeated compression steps was determined using ff-HEDM. Fig. 2 depicts compressive stresses experienced by individual grains over five distinct compression steps. The sandstone grains exhibited resistance to vertical compressive forces while also simultaneously opposing lateral expansion. The specifics of this behavior indicates the emergence of so-called force chains, or stress bridges, in the sandstone sample. Similar force chains also appear in non-cohesive granular materials. This finding is the first to experimentally indicate a similar response to compaction in both sandstone and cohesion-less granular substances.

This study demonstrated the effectiveness of combining synchrotron 3D absorption and diffraction methods to provide new information about the texture, structure, micromechanics, and stress evolution of Nugget sandstone following compaction. This information is vital for characterizing sandstone properties relevant to hydrocarbon extraction and CO₂ storage. Follow-on experiments will involve diverse sample types and stress states. Moreover, recent APS upgrades will allow samples up to one-half centimeter across. – Philip Koth

See: R.C. Hurley¹, Y. Tian^1,2, .M.M. Thakur¹, J-S. Park³, P. Kenesei³, H. Sharma³, A. Gupta¹, K. Lee¹, “Crystallographic texture, structure and stress transmission in nugget sandstone examined with X-ray tomography and diffraction microscopy,” Journal of Geophysical Research: Solid Earth, 130, 7,  e205JB031690 (2025)

Author affiliations: ¹Johns Hopkins University; ²Liaonying Academy of Materials; ³Argonne National Laboratory.

RCH, YT, AG, and KL acknowledge support from the U.S. Department of Energy Grant DE-SC0023024. RCH and YT acknowledge support from the Johns Hopkins Unviersity Catalyst Award. Experiments were performed under General User Proposal (GUP)-81757 at the Advanced Photon Source (APS) beamline ID-1. The authors are grateful for this beamtime. Use of APS, an Office of Science User Facility operated for the U.S. Department of Energy (DOE) Office of Science by Argonne National Laboratory, was supported by the U.S. DOE under Contract No. DE-AC02-06CH11357. 

The U.S. Department of Energy's APS at Argonne National Laboratory is one of the world’s most productive X-ray light source facilities. Each year, the APS provides high-brightness X-ray beams to a diverse community of more than 5,000 researchers in materials science, chemistry, condensed matter physics, the life and environmental sciences, and applied research. Researchers using the APS produce over 2,000 publications each year detailing impactful discoveries and solve more vital biological protein structures than users of any other x-ray light source research facility. APS X-rays are ideally suited for explorations of materials and biological structures; elemental distribution; chemical, magnetic, electronic states; and a wide range of technologically important engineering systems from batteries to fuel injector sprays, all of which are the foundations of our nation’s economic, technological, and physical well-being.

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