# A new mini-triaxial cell for combined high-pressure and high-temperature in situ synchrotron X-ray microtomography experiments up to 400°C and 24 MPa

Marco Voltolini, Harold Barnard, Patrice Creux, Jonathan Ajo-Franklin

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## To cite this version:

Marco Voltolini, Harold Barnard, Patrice Creux, Jonathan Ajo-Franklin. A new mini-triaxial cell for combined high-pressure and high-temperature in situ synchrotron X-ray microtomography experiments up to 400°C and 24 MPa. Journal of Synchrotron Radiation, 2019, 26 (1), pp.238-243. 10.1107/S1600577518015606. hal-02004152

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Submitted on 15 Feb 2026

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# A New Mini-Triaxial Cell for Combined High Pressure and Temperature In-Situ Synchrotron X-ray Micro Tomography experiments up to 400°C and 24 MPa

Marco Voltolini<sup>a</sup>, Harold Barnard<sup>b</sup>, Patrice Creux<sup>c,d</sup>, Jonathan Ajo-Franklin<sup>a</sup>

<sup>a</sup>Earth and Energy Science Area, Energy Geoscience Division, Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, CA 94720, USA.

<sup>b</sup>Advanced Light Source, Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, CA 94720, USA.

<sup>c</sup>Department of Energy Resources Engineering, Stanford University, Stanford, CA 94305, USA.

<sup>d</sup>Laboratoire des Fluides Complexes et leurs Réservoirs-IPRA, UMR5150, CNRS/TOTAL/Univ Pau & Pays Adour, 64000, Pau, France.

## Abstract

A new experimental cell for in situ synchrotron X-ray micro computed tomography, aimed at measuring samples of ~6 mm × 19 mm in size, and able to reach 400 °C in temperature and 24 MPa in pressure, with flow capabilities and pressurization in a fashion similar to triaxial cells, has been developed and tested at the 8.3.2. beamline at the Advanced Light Source. The characteristics of this new experimental rig are described, along with the challenges (mainly concerning X-ray transparency combined with mechanical properties of materials at high temperature) and solutions found during the development stage. An experiment involving oil shale pyrolysis at subsurface conditions, highlighting the importance of a device able to operate in this P/T range, is also introduced. The availability of this cell enables an unprecedented range of experiments in the Earth Sciences, with a special focus on subsurface geothermal processes.

Keywords: X-ray Micro-Tomography, High Pressure and Temperature, In Situ X-ray Imaging, Earth Sciences.
# 1. Introduction

X-ray micro computed tomography (XRµCT), using either conventional or unconventional X-ray sources, is an established experimental technique in the field of the Earth Sciences because of its 3D (or 4D, in case of dynamic systems) visualization capability in a non-destructive fashion, thus enabling the study of a large variety of phenomena at the microscale (Gualda et al., 2010; Cnudde & Boone, 2013 for general reviews). But the success of the technique is due to several factors, beyond the simple 3D visualization. XRµCT data can be used to describe the sample microstructure in a quantitative fashion via morphometric analysis, and several dedicated software packages are available: both commercial (e.g. Avizo®, Visualization Science Group; Dragonfly, Object Research System) or developed by research institutes [e.g. iMorph (Brun & Camille, 2009); Pore3D (Brun et al., 2010)]. More recently, the development of software tools used to simulate experiments starting from XRµCT datasets originated the field of digital rock physics. Modeled properties include ultrasonic wave velocities (Madonna et al., 2012), mercury intrusion porosimetry and drainage in general (Voltoliniª et al., 2017), permeability and electrical conductivity (Andrä et al., 2013), gas flow (Degruyter et al., 2010), etc. opening new opportunities for the geoscientists to better understand the role of morphological features related to specific physical properties. The availability of high brilliance X-ray sources such as synchrotrons, coupled with in situ cells, facilitates 4D XRµCT experiments, where the evolution of the sample is monitored in time. The in situ cells built for SXRµCT experiments can address several variables of interest for the Earth scientist: samples can be imaged when subject to e.g. uniaxial pressure, freezing, heating, reactive flow, etc. A series of examples concerning Earth Sciences where five different variables are investigated is described in Voltoliniᵇ et al. (2017). When considering subsurface processes, two main variables are usually considered: pressure and temperature. In general, in situ cells for XRµCT consider large variations for only one of these parameters, since either heating or compressing a sample often requires a setup not exceedingly complicated. This segment of cells is often focusing towards the extremes, e.g. very high temperatures, which are of interest mostly for volcanologists (Baker et al., 2012; Lee et al., 2016). Pressure-only experimental rigs (uni- and tri- axial) are often used in testing mechanical properties of different materials (e.g. Buffiere et al., 2010), including soils. A third important parameter concerning the subsurface environment is transport: reactive and unreactive flow in rocks is usually studied at room temperature, with or without pressurization. While flow experiments at both ambient P and T can be attained with a simple setup, adding confinement and pore fluid pressures requires more specialized cells. A few research groups developed such in situ cells: a simple low P cell for reactive transport is shown in Voltoliniᵇ et al. (2017), and room or low temperature cells able to operate at high pressure ("high" intended as tens of MPa maximum) for flow have been developed to be used at different synchrotron beamlines (e.g. Menke et al., 2015; Al-Khulaifi et al., 2017; Voltolini et al., 2017ᵃ). Cells with confining pressure have also been used for rock deformation experiments at ~room temperature and different amounts of confining and pore pressures (e.g. Desrues et al., 1996; Viggiani et al., 2004; Renard et al., 2009). Cells combining high pressure and temperature exist (Fusseis et al., 2014), but temperature-wise they are limited to ~200 °C because of material constraints, even if a cell able to operate at significantly high pressure (Renard et al., 2016) has been developed. For extreme high temperatures and pressures, Drickamer-type cells have been employed (Wang et al., 2005), with all the limitations intrinsic to these setups (heavy and bulky, limited sample size, issues with sample rotation, flow, etc.).

A mini-triaxial XRµCT cell breaking the limit of the 200 °C and going up to 400 °C would allow to study processes in the whole hydrothermal temperature (and pressure) range, which is currently not available. This P/T interval is increasing in importance because of the recent geothermal energy impulse, and a significant range of mineralization processes important for the industry
occurs in that range as well. Additionally, geochemical reactions too slow to be observed with in situ measurements can have their reaction rates boosted by an increase in temperature.

In this work we'll describe such a cell able to reach 400 °C at the sample up to 24 MPa in pressure, discussing the solutions employed to solve the various issues encountered during the development, and present an example showing the importance of a cell able to perform measurements in this P/T range.

## 2. Description of the apparatus

The home-designed Mini-Triaxial Cell for Combined High Pressure and Temperature One of the novel elements of this experimental set-up is rotation sample holder.

The full apparatus has been built to fit the 8.3.2. beamline at the Advanced Light Source (ALS) synchrotron, at the Lawrence Berkeley National Laboratory, and it is composed by a pressurization system with three high pressure syringe pumps and relative plumbing, a temperature controller for the heating system of the cell, and the cell main body. The three pumps are shortened (in order to fit underneath the optic table in the experimental hutch) versions of 260D Teledyne Isco pumps and are connected to the cell via 1/16" stainless steel tubing. Two main configurations are available with this three pumps system: 1) The first pump controls the lateral confining pressure, the second one controls the axial load, and the third one controls the pore pressure, all working in constant pressure mode. 2) The first pump is connected to both axial and lateral confining pressure lines, the second is connected to the sample in constant flow mode, the third is connected to the opposite end of the sample and sets the pore pressure. The configuration #1 is used for experiments requiring differential pressure (axial loading deformation, etc.), while #2 typically targets reactive flow experiments (weathering, mineralization, etc.). This flexibility of the system allows for a large range of experiments to be performed. The cell itself is a mini-triaxial cell built by Coretest Systems Inc. (Morgan Hill, CA, USA), and conceptually derived from the cell presented in Voltoliniª et al. (2017). In Fig. 1a the schematics of the cell is displayed. Fig. 2b shows the cell partially dismantled, to highlight the inner baffles system. In Fig. 1c the cell deployed at the beamline during the first experiment is shown. The high temperature cell is built to host cylindrical samples 6.35 mm in diameter, up to 19 mm tall, and the upper and lower stainless steel pistons are sized accordingly. Each piston accommodates a slot for a 50 W heating cartridge, two thermocouple (J-type) slots, and a flow line. On the top of the upper piston, a pressure-driven ram connected to the pump systems provides the axial load. The top assembly also houses a support bracket connected to the piston and a clamp to allow mounting a linear variable differential transformer device (connected to a computer outside the hutch), thus enabling the measurement and recording of the vertical strain in real time during the experiments. The cylindrical sample is included in a thin metal jacket (either titanium grade 5 or annealed copper) connected to the pistons endplugs with conical compression nuts. The sample jacket is surrounded by the inner PEEK or Vespel sleeve, acting as the first thermal insulator. The whole sample assembly is again surrounded by a second PEEK or Vespel sleeve to create a baffle system to prevent thermal loss from the sample. This assembly is included by an Aluminum (7075-T651) outer shell providing the enclosure for the lateral confinement pressure medium. This outer shell is threaded to the Inconel bottom of the body, and a top gland nut system with a Kalrez® O-ring seals the connection with the upper axial piston. The two heating cartridges are controlled by a PTC10 programmable temperature controller (Stanford Research Systems) with J-type thermocouples monitoring the upper and lower piston, and a K-type thermocouple monitoring the temperature of the outer shell, which is actively cooled by a fan system inside of the hutch. For such a cell, the choice of suitable materials was challenging and several problems needed to be addressed simultaneously: especially for the outer shell, the ideal building material needs to be X-ray transparent at the energies available at 8.3.2. (at the sample level), *and* maintain proper mechanical properties to withstand the pressurization while at 400 °C. Concerning the X-ray attenuation issue vs. mechanical strength, the discussion
for the cell presented in Fig.1 in Voltolini<sup>a</sup> et al. (2017) is still valid, but with the non-trivial addition of the temperature issue. Given the X-ray spectrum at 8.3.2. when using filtered white light, peaking at ~30 keV of X-ray energy, the use of dense materials such as found with the titanium shell presented in Renard et al. (2016), aimed at a beamline with significantly harder X-rays, has to be excluded. From the X-ray transparency point of view, plastics are the ideal material, but the polymer with the best mechanical properties at high temperature, Kalrez<sup>®</sup>, is rated up to 327 °C. It has been used only for the seal on the upper piston, where the temperature is higher and the mechanical properties are not essential. Vespel<sup>®</sup> has a slightly lower temperature performance, and it has been chosen for the first sleeve around the sample jacket. Other materials that can be considered for the outer shell are beryllium alloys, which pose significant safety issues related to Be toxicity. Aluminum alloys provide a good X-ray transparency, good mechanical properties, it's safe and easy to work with, but mechanical properties in aluminum alloys tend to degrade above ~150 °C where irreversible modifications in the alloy microstructure start to occur, degrading the mechanical performance (e.g. Summers et al., 2015). Except for this last issue, aluminum was the best candidate, we built the outer shell out of 7075-T651 alloy and engineered a system to avoid the shell reaching above ~100 °C in temperature (being the damage cumulative, we need to stay in a temperature range where the damage develops with an extremely low rate). An active cooling system through an electric fan provides cooling for the outer shell; the baffle system ensures that this cooling only marginally affects the sample, which should be kept at high temperature. The whole cell has been designed to both minimize heat transfer from the pistons and sample to the outer cell to protect the aluminum shell, and to slow thermal diffusion in order to obtain a faster and more homogeneous heating of the sample itself. Another problem arises when considering the confining pressure medium: in triaxial cells pressure media are usually low compressibility fluids, typically water or oil. These fluids are not suitable to be used at 400 °C, therefore we decided to use inert gas (N₂). Gas pressurization has the advantage of lower thermal conductivity, and has lower X-ray attenuation as well, but it stores a much larger amount of energy when compressed and heated, generating safety concerns in case of failure of the cell (a protective shield is in place during the experiments). The two plastic baffle systems set in the space between the sample and the outer aluminum shell efficiently decrease heat transfer. An additional critical issue for the cell was the choice of the sample jacket: plastics cannot be used at 400 °C, so thin (~100 µm) titanium sleeves were tested. These sleeves perform well, but they are extremely stiff, making deformation experiments very difficult. To overcome this problem, we machined copper sleeves of similar thickness. On the other hand, different problems arise from thin copper sleeves: while they are temperature resistant and mechanically soft, allowing to conform and adapt to the sample during pressurization and deformation, their higher X-ray attenuation decreases the quality of the images, they are more prone to puncturing issues (leaks), and they are more chemically reactive. A filler material, such as graphite powder with a very small amount of high-temperature epoxy used as a binding agent, or thin carbon composites sheets, is generally used with the stiff jackets to fill the sample-jacket gap. The combination of these materials provides an adequate X-ray transparency at the sample level, while maintaining the system safe at the highest temperature. The main problem related to image quality with the current setup is the presence of a highly attenuating sample jacket: the quality rapidly decreases close to the outer rim of the sample, because of the increasing length of the path the X-rays need to go through the dense jacket. This issue is effectively minimized by adding a thin layer (~100 µm thick) of more X-ray transparent filler material to avoid having the sample in direct contact with the jacket, since the thickness of the path of the X-rays in the jacket increases ~exponentially from the center of the sample until the inner surface of the jacket, even such a thin layer of material greatly increases the final overall data quality.

The maximum temperature this system can reach, and was also tested in actual experiments, is 400 °C. Pressure-wise our system has been successfully tested up to 15 MPa, but it has been built to reach 24 MPa, with flow capabilities.
## 2.1 Use at the 8.3.2. beamline at ALS

The experimental rig has been tailored to the 8.3.2. beamline at the ALS (MacDowell et al., 2012). As previously mentioned, the three high pressure pumps have been modified to fit underneath the optics table in the experimental hutch, allowing a rapid deployment of the whole system, set on carts. The temperature controller is placed outside, so the temperature can be monitored and varied without the need of opening and closing the hutch. Given the spectrum of the X-ray beam from the insertion device, the cell is intended to be operated using filtered white light, with a 6 mm in line aluminum filter, and a 0.5 mm copper filter placed before the cell. The general sample size was chosen because of the compromise between resolution and field of view (FOV); this specific sample size was chosen to be optimal with the following optics system available at the beamline: 500 µm LuAG scintillator, 2x Mitutoyo objective lenses, PCO-Edge 2560 px × 2560 px CCD detector, resulting in a pixel size of 3.22 µm with a lateral FOV of 8.24 mm, allowing for a full field tomography of the sample, including jacket and some eventual bulging due to deformation, to obtain the full set of boundary conditions in case modeling with the data is required. Vertical FOV is limited by the X-ray beam vertical size and is ~4.5 mm. The system has also been successfully tested with 5× optics in a “local area” setup, with a 1.29 µm px size and 3.3 mm FOV. A high-quality single volume (vertical stacking of multiple volumes is required for taller samples) with 1025 projections in continuous tomography is collected in ~2 minutes, making the data collection of the tallest possible sample last ~15 minutes. Scanning times can be significantly reduced using the available PCO.dmax camera, at expense of image quality, in case of fast evolving systems.

## 3. Oil shale artificial maturation at subsurface pressure conditions

As an application example, we show the main results from an experiment involving Green River oil shale confined pyrolysis. This kind of experiment is extremely important in order to understand natural and artificial (i.e. induced by heating) oil shale maturation (Moyer & Prasad, 2017). Previous experiments of oil shale pyrolysis have been carried out without confinement, and a fracture network development was observed (Panahi et al., 2014; Saif et al., 2016). Results from unconfined experiments cannot be directly extended to reservoirs, where confining pressure plays an important role. In the experiment we are showing, the rigid titanium jacket was used. The sample was heated up to 375 °C, at 13.8 MPa of confining pressure and 5.5 MPa of pore pressure (such large difference was set to test how deformable the titanium jacket is, and eventual leakage issues). The experiment shows that the oil shale at high temperature and pressure displays a markedly plastic behavior, with no fracturing. Fracturing is observed during depressurization and cooling, and at this stage the sample microstructure resembles the one obtained in unconfined experiments. In Fig. 2 (top) a vertical section of the whole sample is shown for three stages: baseline (room temperature), the sample after maximum pressurization and heating, and finally the sample after depressurizing and venting the cell. In Fig. 2 (bottom) three matching horizontal slices of the sample at the three different stages are shown to highlight both the behavior of the sample, and the high quality of the data collected.

## 4. Conclusions

We have presented a new cell aimed at in situ SXRµCT measurements in an unprecedented range of combined pressure and temperature, with flow capabilities. The FOV/resolution range makes it suitable for a large number of experiments in very different fields. Concerning Earth Sciences, this cell enables experiments targeted to high temperature processes in the subsurface. While temperatures related to e.g. magma generation cannot be reached, being able to operate up to 400 °C the whole geothermal temperature spectrum becomes accessible, making new experiments about subsurface high temperature weathering, mineralization, induced seismicity, fracturing,
study of mechanical properties, etc. possible. An example where oil shale was subject to pyrolysis
at subsurface pressure conditions highlighted the importance of having such a P/T range
available: the differences from the confined and unconfined experiments shows that any
interpretation of this process from unconfined experiments cannot be extended to the subsurface,
hence the necessity of new experimental devices such as the one described here.

Acknowledgements

Total S.A. supported the development of the experimental cell through the Stanford Total
Enhanced Modeling of Source Rock (STEMS) project; The Advanced Light Source is supported
by the Director, Office of Science, Office of Basic Energy Sciences, of the US Department of
Energy (award No. DE-AC02-05CH11231).
References

Al-Khulaifi, Y., Lin, Q., Blunt, M.J. and Bijeljic, B., 2017. Reaction rates in chemically heterogeneous rock: Coupled impact of structure and flow properties studied by X-ray microtomography. *Environmental Science & Technology*, 51(7), pp.4108-4116.

Andrä, H., Combaret, N., Dvorkin, J., Glatt, E., Han, J., Kabel, M., Keehm, Y., Krzikalla, F., Lee, M., Madonna, C. and Marsh, M., 2013. Digital rock physics benchmarks—Part II: Computing effective properties. *Computers & Geosciences*, 50, pp.33-43.

Baker, D.R., Brun, F., O'shaughnessy, C., Mancini, L., Fife, J.L. and Rivers, M., 2012. A four-dimensional X-ray tomographic microscopy study of bubble growth in basaltic foam. *Nature Communications*, 3, p.1135.

Brun, E. and Camille, M., 2009. *De l'imagerie 3D des structures à l'étude des mécanismes de transport en milieux cellulaires* (Doctoral dissertation, Aix-Marseille 1).

Brun, F., Mancini, L., Kasae, P., Favretto, S., Dreossi, D. and Tromba, G., 2010. Pore3D: A software library for quantitative analysis of porous media. *Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment*, 615(3), pp.326-332.

Buffiere, J.Y., Maire, E., Adrien, J., Masse, J.P. and Boller, E., 2010. In situ experiments with X ray tomography: an attractive tool for experimental mechanics. *Experimental mechanics*, 50(3), pp.289-305.

Cnudde, V. and Boone, M.N., 2013. High-resolution X-ray computed tomography in geosciences: A review of the current technology and applications. *Earth-Science Reviews*, 123, pp.1-17.

Degruyter, W., Burgisser, A., Bachmann, O. and Malaspinas, O., 2010. Synchrotron X-ray microtomography and lattice Boltzmann simulations of gas flow through volcanic pumices. *Geosphere*, 6(5), pp.470-481.

Fusseis, F., Steeb, H., Xiao, X., Zhu, W.L., Butler, I.B., Elphick, S. and Mäder, U., 2014. A low-cost X-ray-transparent experimental cell for synchrotron-based X-ray microtomography studies under geological reservoir conditions. *Journal of synchrotron radiation*, 21(1), pp.251-253.

Godinho, J., Lee, P., Lavallée, Y., Kendrick, J. and Von-Aulock, F., 2016, April. In situ visualization of magma deformation at high temperature using time-lapse 3D tomography. In *EGU General Assembly Conference Abstracts* (Vol. 18, p. 14369).

Gualda, G.A., Baker, D.R. and Polacci, M., 2010. Introduction: Advances in 3D imaging and analysis of geomaterials. *Geosphere*, 6(5), pp.468-469.

Madonna, C., Almqvist, B.S. and Saenger, E.H., 2012. Digital rock physics: numerical prediction of pressure-dependent ultrasonic velocities using micro-CT imaging. *Geophysical Journal International*, 189(3), pp.1475-1482.

Menke, H.P., Bijeljic, B., Andrew, M.G. and Blunt, M.J., 2015. Dynamic three-dimensional pore-scale imaging of reaction in a carbonate at reservoir conditions. *Environmental science & technology*, 49(7), pp.4407-4414.

Moyer, J. and Prasad, M., 2017. Property changes of oil shale during artificial maturation: The Irati Formation from the Paraná Basin, Brazil. *Geophysics*, 82(6), pp.MR175-MR190.
Panahi, H., Kobchenko, M., Renard, F., Mazzini, A., Scheibert, J., Dysthe, D.K., Jamtveit, B., Malthe-Sørenssen, A. and Meakin, P., 2014. A 4D synchrotron X-ray tomography study of the formation of hydrocarbon migration pathways in heated organic-rich shale. *arXiv preprint arXiv:1401.2448*.

Renard, F., Bernard, D., Desrues, J. and Ougier-Simonin, A., 2009. 3D imaging of fracture propagation using synchrotron X-ray microtomography. *Earth and Planetary Science Letters*, 286(1-2), pp.285-291.

Renard, F., Cordonnier, B., Dysthe, D.K., Boller, E., Tafforeau, P. and Rack, A., 2016. A deformation rig for synchrotron microtomography studies of geomaterials under conditions down to 10 km depth in the Earth. *Journal of synchrotron radiation*, 23(4), pp.1030-1034.

Saif, T., Lin, Q., Singh, K., Bijeljic, B. and Blunt, M.J., 2016. Dynamic imaging of oil shale pyrolysis using synchrotron X-ray microtomography. *Geophysical Research Letters*, 43(13), pp.6799-6807.

Summers, P.T., Chen, Y., Rippe, C.M., Allen, B., Mouritz, A.P., Case, S.W. and Lattimer, B.Y., 2015. Overview of aluminum alloy mechanical properties during and after fires. *Fire Science Reviews*, 4(1), p.3.

Viggiani, G., Lenoir, N., Bésuelle, P., Di Michiel, M., Marello, S., Desrues, J. and Kretzschmer, M., 2004. X-ray microtomography for studying localized deformation in fine-grained geomaterials under triaxial compression. *Comptes rendus Mécanique*, 332(10), pp.819-826.

Voltoliniª, M., Kwon, T.H. and Ajo-Franklin, J., 2017. Visualization and prediction of supercritical CO 2 distribution in sandstones during drainage: An in situ synchrotron X-ray micro-computed tomography study. *International Journal of Greenhouse Gas Control*, 66, pp.230-245.

Voltoliniᵇ, M., Haboub, A., Dou, S., Kwon, T.H., MacDowell, A.A., Parkinson, D.Y. and Ajo-Franklin, J., 2017. The emerging role of 4D synchrotron X-ray micro-tomography for climate and fossil energy studies: five experiments showing the present capabilities at beamline 8.3. 2 at the Advanced Light Source. *Journal of synchrotron radiation*, 24(6).

Voltolini M. and Ajo-Franklin, J., 2018. The Effect of CO₂-Induced Dissolution on Flow Properties in Indiana Limestone: an *In Situ* Synchrotron X-Ray Micro-Tomography Study. *International Journal of Greenhouse Gas Control*. Under review.

Wang, Y., Uchida, T., Westferro, F., Rivers, M.L., Nishiyama, N., Gebhardt, J., Lesher, C.E. and Sutton, S.R., 2005. High-pressure x-ray tomography microscope: Synchrotron computed microtomography at high pressure and temperature. *Review of scientific instruments*, 76(7), p.073709.
## Figure captions

Figure 1.

Section of the schematics of the HP/HT cell (a). The partially dismantled cell, showing the baffle system used to slow heat transfer down (b). The cell mounted onto the rotating stage at the 8.3.2. beamline at the ALS during the first experimental run.

Figure 2.

The evolution of the oil shale sample used during one of the experiments: on the top row the volume rendering of vertical sections of the whole sample are shown for the sample at ambient temperature ("Baseline"), at 13.8 MPa of confining pressure and 5.5 MPa of pore pressure at 375 °C ("High P and T"), and after depressurizing and cooling the sample ("After decompression"). In the bottom row, equivalent horizontal slices from the top part of the sample (see arrow) are displayed.
<figure><img src="image_3.png" /><figcaption>Figure 1.</figcaption></figure>

Section of the schematics of the HP/HT cell (a). The partially dismantled cell, showing the baffle
system used to slow heat transfer down (b). The cell mounted onto the rotating stage at the 8.3.2.
beamline at the ALS during the first experimental run.
<figure><img src="image_4.png" /><figcaption>Figure 2.</figcaption></figure>

The evolution of the oil shale sample used during one of the experiments: on the top row the volume rendering of vertical sections of the whole sample are shown for the sample at ambient temperature (“Baseline”), at 13.8 MPa of confining pressure and 5.5 MPa of pore pressure at 375 °C (“High P and T”), and after depressurizing and cooling the sample (“After decompression”). In the bottom row, equivalent horizontal slices from the top part of the sample (see arrow) are displayed.