Name: stress distribution during cold compression of rocks and mineral aggregates using synchrotron-based x-ray diffraction
Uploaded: 2018-05-20T12:30:00
Description: Watch this Scientific Journal Video about Stress Distribution During Cold Compression of Rocks and Mineral Aggregates Using Synchrotron-based X-Ray Diffraction at JoVE.com

The authors would like to gratefully acknowledge two anonymous peer reviewers and JoVE senior review editor Dr. Alisha DSouza for their invaluable comments. This research was performed at 6-BM-B of the Advanced Photon Source (APS) at Argonne National Laboratory. The use of this facility has been supported by Consortium for Materials Properties Research in Earth Sciences (COMPRES) under National Science Foundation (NSF) cooperative agreement EAR 11-57758, EAR 1661511 and by the Mineral Physics Institute, Stony Brook University. The authors acknowledge NSF for research funding for this program through EAR 1361463, EAR 1045629, and EAR 1141895. This research used resources of the Advanced Photon Source, a U.S. Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by Argonne National Laboratory under contract DEAC02-06CH11357. The cell assemblies are under COMPRES multi-anvil cell assembly development project. All the data files are available from the authors upon request (scheung9@wisc.edu). The samples and data are archived at Mineral Physics Institute at Stony Brook University.

1. Sample Preparation
<ol>
	<li>Choose the test and/or reference sample; this can be either a rock core (step 1.2) or a mineral aggregate (step 1.3), depending the focus of the experimental study. 
	NOTE: The following method is certainly not the only way to prepare good quality samples (e.g., other machines can be used). However, the sample preparation adopted in the present study is fully illustrated to achieve the goal of accurate replication.</li>
	<li>Rock core samples
	<ol>
		<li>Sa...

We present the detailed procedure for carrying out XRD experiments using the multi-anvil cell at 6-BM-B. Perhaps the most critical, and yet most challenging, steps in the above protocol involve optimizing the quality of the sample. Such importance on sample quality applies to almost all rock and mineral deformation experiments. Firstly, it is critical for the end surface of the rock cores to be flat, with both ends parallel to each other and at the same time, perpendicular to the cylindrical surface. That will ensure the...

The rationale behind the method presented in this article is to quantify the stress distribution within rock and mineral aggregate samples during compression and subsequent compaction. Understanding the compaction in rocks and mineral aggregates is of great importance to reservoir and geotechnical engineering8,17,18,19,20,28,33. Compaction acts to reduce porosity, and therefore, leads to an increase in pore pressure. Any such increase in pore pressure leads to a decrease in effective pressure35. The consequence is that it will significantly weaken the reservoir rock, and can therefore be subjected to premature failure at lower stress. Some examples of the resulting consequences of inelastic deformation in the subsurface include: failure in sustaining long term production in oil and gas reservoirs28,33, surface subsidence8,18,19,20, and alteration of fluid flow patterns17. Therefore, a comprehensive knowledge of compaction processes in rocks and mineral aggregates could aid in reducing the possibility of such potentially negative consequences.
The great advantage of using the method highlighted here is that it provides a means to quantify stress distribution internally within a geomaterial5,6 with respect to the globally-averaged externally applied pressure12,22. Moreover, as an in situ experiment, the evolution of the stress distribution is time-resolved. The externally applied pressures considered range from relatively low values (tens of megapascals) to high values (several gigapascals). The stress within the sample is measured indirectly by using the atomic lattice spacing within individual mineral grains as a measure of the local elastic strain5,6. The atomic lattice spacing is determined with the aid of X-radiation, commonly in either the mode of white or monochromatic X-ray. For the white X-ray mode (e.g., DDIA at 6BM-B beamline of the Advanced Photon Source (APS), Argonne National Laboratory), the intensity of the diffracted beam X-ray beam is determined by not just one, but by an array of 10-element Ge detectors (Figure 1) distributed along a fixed circle at azimuthal angles of 0&#176;, 22.5&#176;, 45&#176;, 67.5&#176;, 90&#176;, 112.5&#176;, 135&#176;, 157.5&#176;, 180&#176;, 270&#176;. For the monochromatic X-ray mode, the diffracted pattern is recorded using a CCD detector (e.g., DDIA-30 at 13-ID-D beamline of the GSECARS, APS, Argonne National Laboratory)18,23. Both X-ray modes allow quantification on how the stress varies in different orientations. This approach is fundamentally different from all previous studies of compaction in geomaterials.
In typical compaction studies, a cylindrical sample is compressed by an axial force that is applied across the cross-sectional area by the actuator25. Under such conditions, the magnitude of the applied stress magnitude is generally calculated by simply dividing the axial force (measured by a load cell) by the initial cross-sectional area of the sample. It should be noted that this applied stress magnitude is merely an average, bulk value and, as such, does not realistically represent how the local stress state varies, or is distributed, within a complex, heterogeneous, granular material. Detrital sedimentary rocks, which are examples of complex granular materials, are formed by aggregation of mineral grains that are subsequently compacted and cemented through depositional and diagenetic processes1,7,21,30,31. These aggregates naturally inherit pores that comprise the void spaces between grains, which are intrinsic from the geometry of grain packing modified by secondary dissolution. Hence, any applied stress is expected to be supported by and concentrated at grain-to-grain contacts, and to vanish at grain-pore interfaces.
In addition to the complexity of stress variation within a granular material, other factors further complicate studying compaction in these scenarios. First, the local stress field is vulnerable to any changes due to microstructural artifacts (e.g., grain shape, preexisting fractures) that are inevitably present within any detrital sedimentary rock. Second, although the magnitude of the applied stress acting upon the sample surfaces can be fully quantified, the distribution of stresses within the sample body remained poorly constrained. An end effect32 &#8212; a boundary effect whereby the average stress is concentrated near the contact between the loading rams and the samples due to interface friction &#8212; is well known to be exhibited in cylindrical samples loaded in compression. As an example, Peng26 demonstrated strain heterogeneity within uniaxially compressed granite samples subjected to a variety of end conditions. Hence, to accurately compute the local stress distribution in granular material, we present the following detailed protocol for performing X-ray diffraction (XRD) experiments on rocks and mineral aggregates, using a multi-anvil deformation apparatus at beamline 6-BM-B of the APS at Argonne National Laboratory.

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stress distribution during cold compression of rocks and mineral aggregates using synchrotron-based x-ray diffraction

We report detailed procedures for performing compression experiments on rocks and mineral aggregates within a multi-anvil deformation apparatus (D-DIA) coupled with synchrotron X-radiation. A cube-shaped sample assembly is prepared and compressed, at room temperature, by a set of four X-ray transparent sintered diamond anvils and two tungsten carbide anvils, in the lateral and the vertical planes, respectively. All six anvils are housed within a 250-ton hydraulic press and driven inward simultaneously by two wedged guide blocks. A horizontal energy dispersive X-ray beam is projected through and diffracted by the sample assembly. The beam is commonly in the mode of either white or monochromatic X-ray. In the case of white X-ray, the diffracted X-rays are detected by a solid-state detector array that collects the resulting energy dispersive diffraction pattern. In the case of monochromatic X-ray, the diffracted pattern is recorded using a two-dimensional (2-D) detector, such as an imaging plate or a charge-coupled device (CCD) detector. The 2-D diffraction patterns are analyzed to derive lattice spacings. The elastic strains of the sample are derived from the atomic lattice spacing within grains. The stress is then calculated using the predetermined elastic modulus and the elastic strain. Furthermore, the stress distribution in two-dimensions allow for understanding how stress is distributed in different orientations. In addition, a scintillator in the X-ray path yields a visible light image of the sample environment, which allows for the precise measurement of sample length changes during the experiment, yielding a direct measurement of volume strain on the sample. This type of experiment can quantify the stress distribution within geomaterials, which can ultimately shed light on the mechanism responsible for compaction. Such knowledge has the potential to significantly improve our understanding of key processes in rock mechanics, geotechnical engineering, mineral physics, and material science applications where compactive processes are important.

We show one representative result example from an XRD experiment (experiment SIO2_55) run in the multi-anvil press at 6BM-B on a compound quartz aggregate5,6 and novaculite core sample6. The grain sizes of the quartz aggregate and novaculite are ~4 &#181;m and ~6&#8211;9 &#181;m, respectively5,6. Selected diffraction spectra collected during this ex...

Watch this Scientific Journal Video about Stress Distribution During Cold Compression of Rocks and Mineral Aggregates Using Synchrotron-based X-Ray Diffraction at JoVE.com

Stress Distribution During Cold Compression of Rocks and Mineral Aggregates Using Synchrotron-based X-Ray Diffraction

We report detailed procedures for compression experiments on rocks and mineral aggregates within a multi-anvil deformation apparatus coupled with synchrotron X-radiation. Such experiments allow quantification of the stress distribution within samples, that ultimately sheds light on compaction processes in geomaterials.

We report detailed procedures for performing compression experiments on rocks and mineral aggregates within a multi-anvil deformation apparatus (D-DIA) ...

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