We gratefully thank Abu Dhabi National Oil Company (ADNOC) and ADNOC Onshore (previously known as Abu Dhabi Company for Onshore Petroleum Operations Ltd) for funding this work.

The high resolution X-ray micro-tomography datasets reported in this paper are available at the Digital Rocks Portal: 
www.digitalrocksportal.org/projects/151&#160; 
The codes used to run automatic measurements of contact angle and fluid/fluid interface curvature are available at GitHub: 
https://github.com/AhmedAlratrout/ContactAngle-Curvature-Roughness&#160;

The most critical steps for an in situ wettability characterization at high pressure and temperature to be successful are as follows. 1) Generate a good image segmentation that is essential to obtain accurate contact angle measurements. 2) Avoid including large impermeable grains in the mini-samples that could seal off the flow, and large vugs resulting in a very fragile sample with non-representative porosity. 3) A well-controlled flow experiment with no leaks is important because mini-samples are very sensitive to the amount of injected fluid (i.e., one pore volume is about 0.1 mL). 4) Avoid the presence of air (as a fourth phase) in the pore space. 5) Maintain a temperature control of the sample during the whole flow experiment. 6) Avoid any interface relaxation during the scan acquisition by waiting for the system to reach equilibrium. 7) Use an appropriate center shift correction, which is necessary for the effective X-ray image reconstruction.
The automated contact angle method is limited by the accuracy of the image segmentation because it is applied to segmented images only. Image segmentation depends largely on imaging quality that depends on the imaging protocol and the performance of the microtomography scanner. Furthermore, it is sensitive to the image reconstruction and the noise reduction filters, as well as the segmentation method such as the TWS32 or the seeded watershed method57. In this work, the TWS method provided more accurate contact angle measurements on raw X-ray images compared to those by a watershed method applied to filtered X-ray images (using noise reduction filters). The use of noise reduction filters makes the interface appear to be less oil-wet at some parts of the rock, due to the voxel averaging especially close to the three-phase contact line31. TWS can capture not only the amount of remaining oil saturation but also the shape of the remaining oil ganglia. This is especially the case for the remaining oil in the mixed-wet cases, in which oil is retained in the pore space as thin sheet-like structures, making it a challenge to be segmented based on gray-scale threshold values only.
This in situ wettability determination provides a thorough description of the wetting conditions of reservoir rocks compared to other conventional wettability measurement methods. It takes into account all important pore-scale rock parameters, such as rock surface roughness, rock chemical compositions, and pore size and geometry, that are not possible by wettability indices7,8&#160;and ex situ contact angle methods4,9,10,11. The use of an automated in situ contact angle measurement at the micron scale is robust and removes any subjectivity associated with the manual method24. Moreover, it is more effective in removing voxelization artefacts compared to other automated methods25,26. The in situ contact angle distribution measured using the automated method was relatively rapid. For example, the runtime for measuring the contact angle on any of the three sample images that contain 595 million voxels is approximately 2 h, using a single 2.2&#8239;GHz CPU processor.
In the future, this protocol can be used to characterize other reservoir rock systems saturated with formation brine and crude oil. The same method is not limited to the petroleum industry only and can be modified and adapted to characterize the wettability from any segmented three-dimensional images with two immiscible fluids in porous media with a variety of wettability conditions.

Wettability (the contact angle between immiscible fluids at a solid surface) is one of the key properties that control fluid configurations and oil recovery in reservoir rocks. Wettability affects macroscopic flow properties including relative permeability and capillary pressure1,2,3,4,5,6. However, measuring the in situ wettability of reservoir rock has remained a challenge. Reservoir rock wettability has been determined traditionally at the core scale, indirectly using wettability indices7,8, and directly ex situ on flat mineral surfaces4,9,10,11. Both wettability indices and ex situ contact angle measurements are limited and cannot characterize the mixed-wettability (or range of contact angle) that typically exist in hydrocarbon reservoirs. Moreover, they do not account for pore-scale rock properties, such as rock mineralogy, surface roughness, pore-geometry, and spatial heterogeneity, that have a direct impact on the fluid arrangement at the pore scale.
Recent advances in non-invasive three-dimensional imaging using X-ray microtomography12, in combination with the use of an elevated temperature and&#160;pressure apparatus13, have allowed the study of multiphase flow in permeable media14,15,16,17,18,19,20,21,22,23. This technology has facilitated the development of manual in situ contact angle measurements at the pore scale in an opaque porous medium (quarry limestone rock) at subsurface conditions24. A mean contact angle value of 45&#176; &#177; 6&#176; between CO2 and potassium iodide (KI) brine was obtained by hand from raw images at 300 points. However, the manual method is time-consuming (i.e., 100 contact angle points could take up to several days to be measured) and the values obtained could have a subjective bias.
The measurement of an in situ contact angle has been automated by different methods applied to segmented three-dimensional X-ray images25,26,27. Scanziani et al.25 improved the manual method by placing a circle at the fluid-fluid interface that intersects with a line placed at the fluid-rock interface on slices orthogonal to the three-phase contact line. This method has been applied to small sub-volumes extracted from three-dimensional images of quarry limestone rock saturated with decane and KI brine. Klise et al.26 developed a method to quantify the in situ contact angle automatically by fitting planes to the fluid-fluid interfaces and fluid-rock interfaces. The contact angle was determined between these planes. This method was applied to three-dimensional images of beads saturated with kerosene and brine. Both automated methods were applied to voxelized images that might introduce error, and in both methods, lines or planes were fitted at the fluid-fluid and fluid-rock interfaces and the contact angle was measured between them. Applying these two approaches on voxelized segmented images of complex rock geometry could lead to errors while also being time-consuming.
In this protocol, we apply the automated in situ contact angle method developed by AlRatrout et al.27 that removes voxelization artefacts by applying Gaussian smoothing to the fluid-fluid and fluid-solid interfaces. Then, a uniform curvature smoothing is applied only to the fluid-fluid interface, which is consistent with the capillary equilibrium. Hundreds of thousands of contact angle points are measured rapidly in combination with their x-, y-, and z-coordinates. The approach of AlRatrout et al.27 has been applied to water-wet and mixed-wet quarry limestone samples saturated with decane and KI brine.
In this protocol, we employ the latest advances in X-ray microtomography combined with a high-pressure and high-temperature apparatus to conduct an in situ wettability characterization of complex carbonate reservoir rocks, extracted from a very large producing oil field located in the Middle East. The rocks were saturated with crude oil at subsurface conditions to reproduce the reservoir conditions upon discovery. It has been hypothesized that parts of the reservoir rock surfaces (with direct contact with crude oil) become oil-wet, while others (filled with initial formation brine) remain water-wet28,29,30. However, the reservoir rock wettability is even more complex due to several factors controlling the degree of wettability alteration, including the surface roughness, the rock chemical heterogeneity, the crude oil composition, the brine composition and saturation, and the temperature and pressure. A recent study31 has shown that there is typically a range of contact angle in reservoir rocks with values both above and below 90&#176;, measured using the automated method developed by AlRatrout et al.27.
The main objective of this work is to provide a thorough protocol to characterize the in situ wettability of reservoir rocks (mixed-wettability) at subsurface conditions. An accurate measurement of an in situ contact angle requires a good segmentation quality. Hence, a machine learning-based segmentation method known as Trainable WEKA Segmentation (TWS)32 was used to capture not only the amount of remaining oil but also the shape of the remaining oil ganglia, thus facilitating more accurate contact angle measurements. Recently, TWS has been used in a variety of applications, such as the segmentation of packed particle beds, liquids within textile fibers, and pores of tight reservoirs33,34,35,36,37,38,39,40. To image the remaining oil accurately at a high resolution and at subsurface conditions, a novel experimental apparatus was used (Figure&#160;1 and Figure&#160;2). Mini-samples of rock were loaded into the center of a Hassler-type core holder41 made of carbon fiber. The use of a long and small diameter carbon fiber sleeve allows an X-ray source to be brought very close to the sample, hence increasing the X-ray flux and reducing the required exposure time, resulting in a better image quality in a shorter period of time. The carbon fiber sleeve is strong enough to handle high pressure and temperature conditions while remaining sufficiently transparent to X-rays21.
In this study, we outline the steps followed to characterize the in situ wettability of reservoir rocks at subsurface conditions. This includes drilling representative mini-samples, the core holder assembly, the flow apparatus and flow procedure, the imaging protocol, the image processing and segmentation, and finally running the automated contact angle code to generate contact angle distributions.

<table><tbody><tr><td>Xradia VersaXRM-500 X-ray micro-CT</td><td>ZEISS</td><td>Quote</td><td>X-ray microtomography scanner, https://www.zeiss.com/microscopy/int/products/x-ray-microscopy.html</td></tr><tr><td>Teledyne Isco syringe pumps</td><td>Teledyne Isco</td><td>Quote</td><td>Model 100DM, Model 260D and Model 1000D, http://www.teledyneisco.com/en-uk</td></tr><tr><td>Core holder</td><td>Airborne</td><td>Quote</td><td>9.5 ID Coreholder, www.airborne-international.com</td></tr><tr><td>Gas pycnometer</td><td>Micromeritics</td><td>Quote</td><td>AccuPyc II 1340 Pycnometer, http://www.micromeritics.com/Product-Showcase/AccuPyc-II-1340.aspx</td></tr><tr><td>Thermocouple</td><td>Omega</td><td>KMTSS-IM025U-150</td><td>0.25 to 1.0 mm Fine Diameter MI Construction Thermocouples Terminated With A Mini Pot-Seal and 1m PFA Lead Wire, https://www.omega.co.uk/pptst/TJMINI_025-075MM_IEC.html</td></tr><tr><td>Flexible heating jacket</td><td>Omega</td><td>KH-112/5-P</td><td>Kapton Insulated Flexible Heaters, https://www.omega.co.uk/pptst/KHR_KHLV_KH.html</td></tr><tr><td>PEEK tubing</td><td>Kinesis</td><td>1533XL</td><td>PEEK Tubing 1/16&amp;rdquo;OD X 0.030&amp;rdquo; (0.75mm) ID Green, http://kinesis.co.uk/tubing-tubing-peek-green-1-16-x-0-030-0-75mm-x100ft-1533xl.html</td></tr><tr><td>Tube cutter</td><td>Kinesis</td><td>003062</td><td>Tube cutter, http://kinesis.co.uk/tubing-tube-cutter-003062.html</td></tr><tr><td>PEEK fingertight fitting</td><td>Kinesis</td><td>F-120X</td><td>Fingertight Fitting, single piece, for 1/16&quot; OD Tubing, 10-32 Coned, PEEK, Natural, http://kinesis.co.uk/fingertight-fitting-single-piece-for-1-16-od-tubing-10-32-coned-peek-natural-f-120x.html</td></tr><tr><td>PEEK adapters and connectors</td><td>Kinesis</td><td>P-760</td><td>Adapters &amp;amp; Connectors: PEEK&amp;trade; ZDV Union, for 1/16&quot; OD Tubing, 10-32 Coned, http://kinesis.co.uk/catalogsearch/result/?q=P-760</td></tr><tr><td>PEEK plug</td><td>Kinesis</td><td>P-551</td><td>Plug, 10-32 Coned, PEEK, Natural, http://kinesis.co.uk/plug-10-32-coned-peek-natural-p-551.html</td></tr><tr><td>Digital Caliper</td><td>RS</td><td>50019630</td><td>Digital caliper, http://uk.rs-online.com/web/</td></tr><tr><td>Three-way valve</td><td>Swagelok</td><td>SS-41GXS1</td><td>Stainless Steel 1-Piece 40G Series 3-Way Ball Valve, 0.08 Cv, 1/16 in. Swagelok Tube Fitting, https://www.swagelok.com/en/catalog/Product/Detail?part=SS-41GXS1</td></tr><tr><td>Viton sleeve</td><td>Cole-Parmer</td><td>WZ-06435-03</td><td>Viton FDA Compliant Tubing, 3/16&quot; (4.8 mm) ID, https://www.coleparmer.com/i/mn/0643503</td></tr><tr><td>Drilling bit</td><td>dk-holdings</td><td>quote</td><td>Standard wall drill *EDS540, 5mm internal diameter x continental shank, reinforced stepped shank 5mm of the tube behind 20mm of diamond, http://www.dk-holdings.co.uk/glass/stanwall.html</td></tr><tr><td>Heptane</td><td>Sigma-Aldarich</td><td>246654-1L</td><td>Heptane, anhydrous, 99%, http://www.sigmaaldrich.com/catalog/product/sial/246654?lang=en&amp;amp;region=GB</td></tr><tr><td>Potassium iodide</td><td>Sigma-Aldarich</td><td>231-659-4&amp;nbsp;</td><td>purity &amp;ge; 99.0%, https://www.sigmaaldrich.com/catalog/product/sigma/60399?lang=en&amp;amp;region=GB</td></tr><tr><td>ParaView</td><td>Open source</td><td>Free</td><td>Data visiualization software (Protocol step 6.6), https://www.paraview.org/</td></tr><tr><td>Avizo Software</td><td>FEI</td><td>License</td><td>Data visiualization and analysis software (Protocol step 1.2, 5.7.1), https://www.fei.com/software/amira-avizo/</td></tr><tr><td>Recontructor Software</td><td>ZEISS</td><td>License</td><td>https://www.zeiss.com/</td></tr></tbody></table>

pore-scale imaging and characterization of hydrocarbon reservoir rock wettability at subsurface conditions using x-ray microtomography

In situ wettability measurements in hydrocarbon reservoir rocks have only been possible recently. The purpose of this work is to present a protocol to characterize the complex wetting conditions of hydrocarbon reservoir rock using pore-scale three-dimensional X-ray imaging at subsurface conditions. In this work, heterogeneous carbonate reservoir rocks, extracted from a very large producing oil field, have been used to demonstrate the protocol. The rocks are saturated with brine and oil and aged over three weeks at subsurface conditions to replicate the wettability conditions that typically exist in hydrocarbon reservoirs (known as mixed-wettability). After the brine injection, high-resolution three-dimensional images (2 &#181;m/voxel) are acquired and then processed and segmented. To calculate the distribution of the contact angle, which defines the wettability, the following steps are performed. First, fluid-fluid and fluid-rock surfaces are meshed. The surfaces are smoothed to remove voxel artefacts, and in situ contact angles are measured at the three-phase contact line throughout the whole image. The main advantage of this method is its ability to characterize in situ wettability accounting for pore-scale rock properties, such as rock surface roughness, rock chemical composition, and pore size. The in situ wettability is determined rapidly at hundreds of thousands of points. 
The method is limited by the segmentation accuracy and X-ray image resolution. This protocol could be used to characterize the wettability of other complex rocks saturated with different fluids and at different conditions for a variety of applications. For example, it could help in determining the optimal wettability that could yield an extra oil recovery (i.e., designing brine salinity accordingly to obtain higher oil recovery) and to find the most efficient wetting conditions to trap more CO2 in subsurface formations.

For the 3 samples studied, the measured in situ distribution of the contact angle is shown in Figure 6, with the oil recovery shown in Figure 11. Figure 12 shows images of the remaining oil distributions for different wetting conditions at the end of the waterflooding. The mixed-wettability (or the range of the contact angle) was measured using the automated contact angle method27. The measured contact angle distributions are considered to be representative results if there is a good match between the contact angle points measured using the automated method from segmented images compared to the manually measured contact angles from raw X-ray images. Figure 10 shows an example of a good match of a comparison measurement between the automated contact angles and the manual contact angles at the same locations for a sub-volume from mini-sample 1 (weakly water-wet).
Three aging protocols were performed to treat the 3 samples and generate 3 wetting conditions (Figure 6). Aging the sample at a lower temperature (60 &#176;C) and statically (no oil injection during the aging period) could result in a weakly water-wet condition, such as the distribution shown for sample 1 in blue (Figure 6). On the other hand, aging the sample at a higher temperature (80 &#176;C) and with partially dynamic aging (an oil injection during the aging period) could result in mixed-wet conditions with more oil-wet surfaces, like that of sample 2 shown in gray (Figure 6).
The oil recovery was found to be a function of wettability, similar to earlier core-scale studies51. However, at that time, the oil recovery was shown as a function of the core-scale wettability index. Similar oil recovery behavior has been observed at the pore scale and was plotted as a function of the mean value of the in situ contact angle distribution (Figure 11). The low oil recovery of sample 1 (weakly water-wet) was due to the trapping of oil in larger pore spaces. The brine percolated through the small pore corners, leaving the oil trapped as disconnected ganglia in the center of the pore spaces with quasi-spherical shapes (Figure 12a), similar to what has been observed in previous investigations in water-wet media52,53,54,55. In contrast, sample 2 (a mixed-wet case with more oil-wet surfaces) had oil layers that were largely connected (Figure 12b). These thin layers only allowed a slow oil production, leaving a high remaining oil saturation at the end of the waterflooding. The highest oil recovery was achieved in sample 3 (mixed-wet with a mean contact angle close to 90&#176;) which was neither water-wet (so there is less trapping in large pores) nor strongly oil-wet (less oil is retained in small pore spaces)1. In the mixed-wet cases of sample 2 and 3, oil was left in connected, thin sheet-like structures (Figure&#160;12b and 12c) similar to other studies in oil-wet porous media52,53,56.
<img alt="Figure 1" class="xfigimg" src="/files/ftp_upload/57915/57915fig1.jpg" /> 
Figure 1: A schematic illustration diagram of the core holder assembly. Components of the core holder are labeled, and the internal cross-section view of the core holder is shown. <a href="https://www.jove.com/files/ftp_upload/57915/57915fig1large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 2" class="xfigimg" src="/files/ftp_upload/57915/57915fig2.jpg" /> 
Figure 2: The high-pressure, high-temperature flow apparatus. The flow apparatus is comprised of four high-pressure syringe pumps: (A) an oil pump, (B) a receiving pump, (C) a brine pump, and (D) a confining pump. Panel (E) shows the core holder assembly, (F) shows the PID controller, and (G) shows the CO2 cylinder. <a href="https://www.jove.com/files/ftp_upload/57915/57915fig2large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 3" class="xfigimg" src="/files/ftp_upload/57915/57915fig3.jpg" /> 
Figure 3: Images demonstrating the drilling of representative mini-samples. (a) This cartoon illustrates the orthogonal marks with a good drilling location. x and y are the distances from the center of the core plug used to find where to drill. (b) This panel shows a dry X-ray three-dimensional image of the core plug (rendered semi-transparent) with a mini-sample (in dark gray). (c) This is a horizontal cross-sectional view of the core plug (scanned at 40 &#181;m/voxel). The rock grains and pores are shown in gray and black, respectively. (d) This panel shows a horizontal cross-sectional view&#160;of the mini-sample (scanned at 5.5 &#181;m/voxel). (e) This is a vertical cross-sectional view of the core plug showing the complex and heterogeneous pore sizes and geometries along with the location of the mini-sample indicated by the black box. (f) This is a magnified vertical cross-sectional view of the highlighted mini-sample shown in panel e that was scanned at 5.5 &#181;m/voxel. <a href="https://www.jove.com/files/ftp_upload/57915/57915fig3large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 4" class="xfigimg" src="/files/ftp_upload/57915/57915fig4.jpg" /> 
Figure 4: A phase contrast scan. (a) This panel shows a contrast scan of crushed rock (light gray) mixed with brine (dark gray) and oil (black) phases. This was used to determine the appropriate doping of the brine to ensure a good phase contrast. (b) This is a histogram of the gray-scale value of the three phases. <a href="https://www.jove.com/files/ftp_upload/57915/57915fig4large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 5" class="xfigimg" src="/files/ftp_upload/57915/57915fig5.jpg" /> 
Figure 5: A horizontal cross-sectional view of raw and segmented X-ray images of three mini-samples. Panels (a), (b), and (c) show xy cross-sectional views of mini-samples 1, 2, and 3, respectively. The top row shows the raw gray-scale X-ray images (oil, brine, and rock, are in black, dark gray, and light gray, respectively). The lower images show the segmented images of the same slice using Trainable WEKA Segmentation (oil, brine, and rock, are in black, gray, and white, respectively). <a href="https://www.jove.com/files/ftp_upload/57915/57915fig5large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 6" class="xfigimg" src="/files/ftp_upload/57915/57915fig6.jpg" /> 
Figure 6: Distributions of the contact angle measurement of the three mini-samples. Sample 1 has a mean contact angle of 77&#176; &#177; 21&#176; with 462,000 values shown in blue. Sample 2 has a mean contact angle of 104&#176; &#177; 26&#176; with 1.41 million values shown in gray. Sample 3 has a mean contact angle of 94&#176; &#177; 24&#176; with 769,000 values shown in red. <a href="https://www.jove.com/files/ftp_upload/57915/57915fig6large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 7" class="xfigimg" src="/files/ftp_upload/57915/57915fig7.jpg" /> 
Figure 7: The workflow for an automated contact angle measurement. (a) This is a three-dimensional segmented image showing brine in blue and oil in red, while rock is rendered transparent. (b) This panel shows extracted surfaces of the whole image. The oil/brine surfaces are shown in green, while the oil/rock surfaces are shown in red. (c) This panel shows the smoothed surfaces of the whole image. (d) This panel shows the three-phase contact line of the whole image. (e) This is an example of the smoothed surfaces of an oil ganglion highlighted by the black square. (f) This panel shows the three-phase contact line of the highlighted oil ganglion. (g) This is an example of a single contact angle measuring at point i (highlighted in panel f). The oil/brine, oil/rock, and brine/rock surfaces are shown in green, red, and blue, respectively. <a href="https://www.jove.com/files/ftp_upload/57915/57915fig7large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 8" class="xfigimg" src="/files/ftp_upload/57915/57915fig8.jpg" /> 
Figure 8: Three sub-volumes extracted from the three mini-samples. (a) This panel shows the sub-volume extracted from mini-sample 1 (weakly water-wet). (b) This panel shows the sub-volume extracted from mini-sample 2 (mixed-wet). (c) This panel shows the sub-volume extracted from mini-sample 3 (mixed-wet). <a href="https://www.jove.com/files/ftp_upload/57915/57915fig8large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 9" class="xfigimg" src="/files/ftp_upload/57915/57915fig9.jpg" /> 
Figure 9: A one-to-one contact angle measurement workflow. (a) This is a visualization of a randomly selected contact angle point (60&#176;) measured using the automated code (the image is obtained from the data visualization software used). (b) This panel shows how to identify the location of the same point using the data visualization and analysis software. (c) This panel shows how to conduct a manual contact angle measurement at the same location. (d) This is an example of the manually measured contact angle point at the same location (61&#176;). <a href="https://www.jove.com/files/ftp_upload/57915/57915fig9large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 10" class="xfigimg" src="/files/ftp_upload/57915/57915fig10.jpg" /> 
Figure 10: Automated contact angle measurements compared to the manual contact angle measurements at the same locations of the sub-volume from mini-sample 1. The values were measured following the procedure described in Figure 9. <a href="https://www.jove.com/files/ftp_upload/57915/57915fig10large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 11" class="xfigimg" src="/files/ftp_upload/57915/57915fig11.jpg" /> 
Figure 11: Oil recovery as a function of wettability. The oil recoveries of sample 1, 2, and 3 are 67.1%, 58.6%, and 84.0%, respectively. <a href="https://www.jove.com/files/ftp_upload/57915/57915fig11large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 12" class="xfigimg" src="/files/ftp_upload/57915/57915fig12.jpg" /> 
Figure 12: The remaining oil morphology for different wetting conditions. (a) In sample 1 (weakly water-wet), the remaining oil was trapped at the center of the pores as disconnected ganglia with quasi-spherical shapes. Panels (b) and (c) show how in samples 2 and 3 (mixed-wet), the remaining oil was left in connected, thin sheet-like structures in small pores and crevices. The different colors represent disconnected oil ganglia. <a href="https://www.jove.com/files/ftp_upload/57915/57915fig12large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>

Watch this Scientific Journal Video about Pore-scale Imaging and Characterization of Hydrocarbon Reservoir Rock Wettability at Subsurface Conditions Using X-ray Microtomography at JoVE.com

Pore-scale Imaging and Characterization of Hydrocarbon Reservoir Rock Wettability at Subsurface Conditions Using X-ray Microtomography

This protocol is presented to characterize the complex wetting conditions of an opaque porous medium (hydrocarbon reservoir rock) using three-dimensional images obtained by X-ray microtomography at subsurface conditions.

In situ wettability measurements in hydrocarbon reservoir rocks have only been possible recently. The purpose of this work is to present a protocol to ...

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13.8K Views.  Imperial College London. Het algemene doel van dit werk is om een grondig protocol te bieden om de in situ nattigheid van reservoirrotsen bij ondergrondse omstandigheden te karakteriseren. Deze methode kan helpen bij het beantwoorden van belangrijke vragen in multifase stroom poreuze media met toepassing op olieterugwinning, verontreiniging verwijdering en kooldioxide opslag. Het belangrijkste voordeel van deze techniek is dat we verplaatsingsprocessen en nattigheid in natuurlijke systemen kunnen bestuderen.Di...

Video: Pore-scale Imaging and Characterization of Hydrocarbon Reservoir Rock Wettability at Subsurface Conditions Using X-ray Microtomography

Characterization of Electrode Materials for Lithium Ion and Sodium Ion Batteries Using Synchrotron Radiation Techniques

Intercalation compounds such as transition metal oxides or phosphates are the most commonly used electrode materials in Li-ion and Na-ion batteries. During insertion or removal of alkali metal ions, the redox states of transition metals in the compounds change and structural transformations such as phase transitions and/or lattice parameter increases or decreases occur. These behaviors in turn determine important characteristics of the batteries such as the potential profiles, rate capabilities, and cycle lives. The extremely bright and tunable x-rays produced by synchrotron radiation allow rapid acquisition of high-resolution data that provide information about these processes. Transformations in the bulk materials, such as phase transitions, can be directly observed using X-ray diffraction (XRD), while X-ray absorption spectroscopy (XAS) gives information about the local electronic and geometric structures (e.g.&#160;changes in redox states and bond lengths). In situ experiments carried out on operating cells are particularly useful because they allow direct correlation between the electrochemical and structural properties of the materials. These experiments are time-consuming and can be challenging to design due to the reactivity and air-sensitivity of the alkali metal anodes used in the half-cell configurations, and/or the possibility of signal interference from other cell components and hardware. For these reasons, it is appropriate to carry out ex situ experiments (e.g.&#160;on electrodes harvested from partially charged or cycled cells) in some cases. Here, we present detailed protocols for the preparation of both ex situ and in situ samples for experiments involving synchrotron radiation and demonstrate how these experiments are done.

We describe the use of synchrotron X-ray absorption spectroscopy (XAS) and X-ray diffraction (XRD) techniques to probe details of intercalation/deintercalation processes in electrode materials for Li-ion and Na-ion batteries. Both in situ and ex situ experiments are used to understand structural behavior relevant to the operation of devices

Intercalation compounds such as transition metal oxides or phosphates are the most commonly used electrode materials in Li-ion and Na-ion batteries. ...

Reservoir Condition Pore-scale Imaging of Multiple Fluid Phases Using X-ray Microtomography

X-ray microtomography was used to image, at a resolution of 6.6 &#181;m, the pore-scale arrangement of residual carbon dioxide ganglia in the pore-space of a carbonate rock at pressures and temperatures representative of typical formations used for CO2 storage. Chemical equilibrium between the CO2, brine and rock phases was maintained using a high pressure high temperature reactor, replicating conditions far away from the injection site. Fluid flow was controlled using high pressure high temperature syringe pumps. To maintain representative in-situ conditions within the micro-CT scanner a carbon fiber high pressure micro-CT coreholder was used. Diffusive CO2 exchange across the confining sleeve from the pore-space of the rock to the confining fluid was prevented by surrounding the core with a triple wrap of aluminum foil. Reconstructed brine contrast was modeled using a polychromatic x-ray source, and brine composition was chosen to maximize the three phase contrast between the two fluids and the rock. Flexible flow lines were used to reduce forces on the sample during image acquisition, potentially causing unwanted sample motion, a major shortcoming in previous techniques. An internal thermocouple, placed directly adjacent to the rock core, coupled with an external flexible heating wrap and a PID controller was used to maintain a constant temperature within the flow cell. Substantial amounts of CO2 were trapped, with a residual saturation of 0.203 &#177; 0.013, and the sizes of larger volume ganglia obey power law distributions, consistent with percolation theory.

We present a methodology for the imaging of multiple fluid phases at reservoir conditions by the use of x-ray microtomography. We show some representative results of capillary trapping in a carbonate rock sample.

X-ray microtomography was used to image, at a resolution of 6.6 &#181;m, the pore-scale arrangement of residual carbon dioxide ganglia in the pore-space ...

Energy Dispersive X-ray Tomography for 3D Elemental Mapping of Individual Nanoparticles

Energy dispersive X-ray spectroscopy within the scanning transmission electron microscope (STEM) provides accurate elemental analysis with high spatial resolution, and is even capable of providing atomically resolved elemental maps. In this technique, a highly focused electron beam is incident upon a thin sample and the energy of emitted X-rays is measured in order to determine the atomic species of material within the beam path. This elementally sensitive spectroscopy technique can be extended to three dimensional tomographic imaging by acquiring multiple spectrum images with the sample tilted along an axis perpendicular to the electron beam direction.
Elemental distributions within single nanoparticles are often important for determining their optical, catalytic and magnetic properties. Techniques such as X-ray tomography and slice and view energy dispersive X-ray mapping in the scanning electron microscope provide elementally sensitive three dimensional imaging but are typically limited to spatial resolutions of &gt; 20 nm. Atom probe tomography provides near atomic resolution but preparing nanoparticle samples for atom probe analysis is often challenging. Thus, elementally sensitive techniques applied within the scanning transmission electron microscope are uniquely placed to study elemental distributions within nanoparticles of dimensions 10-100 nm.
Here, energy dispersive X-ray (EDX) spectroscopy within the STEM is applied to investigate the distribution of elements in single AgAu nanoparticles. The surface segregation of both Ag and Au, at different nanoparticle compositions, has been observed.

The use of energy dispersive X-ray tomography in the scanning transmission electron microscope to characterize elemental distributions within single nanoparticles in three dimensions is described.

Energy dispersive X-ray spectroscopy within the scanning transmission electron microscope (STEM) provides accurate elemental analysis with high spatial ...

Failure Analysis of Batteries Using Synchrotron-based Hard X-ray Microtomography

Imaging morphological changes that occur during the lifetime of rechargeable batteries is necessary to understand how these devices fail. Since the advent of lithium-ion batteries, researchers have known that the lithium metal anode has the highest theoretical energy density of any anode material. However, rechargeable batteries containing a lithium metal anode are not widely used in consumer products because the growth of lithium dendrites from the anode upon charging of the battery causes premature cell failure by short circuit. Lithium dendrites can also form in commercial lithium-ion batteries with graphite anodes if they are improperly charged. We demonstrate that lithium dendrite growth can be studied using synchrotron-based hard X-ray microtomography. This non-destructive imaging technique allows researchers to study the growth of lithium dendrites, in addition to other morphological changes inside batteries, and subsequently develop methods to extend battery life.

Synchrotron-based hard X-ray microtomography is used to image the electrochemical growth of dendrites from a lithium metal electrode through a solid polymer electrolyte membrane.

Imaging morphological changes that occur during the lifetime of rechargeable batteries is necessary to understand how these devices fail. Since the advent ...

Measurement of X-ray Beam Coherence along Multiple Directions Using 2-D Checkerboard Phase Grating

A procedure for a technique to measure the transverse coherence of synchrotron radiation X-ray sources using a single phase grating interferometer is reported. The measurements were demonstrated at the 1-BM bending magnet beamline of the Advanced Photon Source (APS) at Argonne National Laboratory (ANL). By using a 2-D checkerboard &#960;/2 phase-shift grating, transverse coherence lengths were obtained along the vertical and horizontal directions as well as along the 45&#176; and 135&#176; directions to the horizontal direction. Following the technical details specified in this paper, interferograms were measured at different positions downstream of the phase grating along the beam propagation direction. Visibility values of each interferogram were extracted from analyzing harmonic peaks in its Fourier Transformed image. Consequently, the coherence length along each direction can be extracted from the evolution of visibility as a function of the grating-to-detector distance. The simultaneous measurement of coherence lengths in four directions helped identify the elliptical shape of the coherence area of the Gaussian-shaped X-ray source. The reported technique for multiple-direction coherence characterization is important for selecting the appropriate sample size and orientation as well as for correcting the partial coherence effects in coherence scattering experiments. This technique can also be applied for assessing coherence preserving capabilities of X-ray optics.

The measurement protocol and data analysis procedure are given for obtaining transverse coherence of a synchrotron radiation X-ray source along four directions simultaneously using a single 2-D checkerboard phase grating. This simple technique can be applied for complete transverse coherence characterization of X-ray sources and X-ray optics.

A procedure for a technique to measure the transverse coherence of synchrotron radiation X-ray sources using a single phase grating interferometer is ...

Microfluidic Devices for Characterizing Pore-scale Event Processes in Porous Media for Oil Recovery Applications

Microfluidic devices are versatile tools for studying transport processes at a microscopic scale. A demand exists for microfluidic devices that are resistant to low molecular-weight oil components, unlike traditional polydimethylsiloxane (PDMS) devices. Here, we demonstrate a facile method for making a device with this property, and we use the product of this protocol for examining the pore-scale mechanisms by which foam recovers crude oil. A pattern is first designed using computer-aided design (CAD) software and printed on a transparency with a high-resolution printer. This pattern is then transferred to a photoresist via a lithography procedure. PDMS is cast on the pattern, cured in an oven, and removed to obtain a mold. A thiol-ene crosslinking polymer, commonly used as an optical adhesive (OA), is then poured onto the mold and cured under UV light. The PDMS mold is peeled away from the optical adhesive cast. A glass substrate is then prepared, and the two halves of the device are bonded together. Optical adhesive-based devices are more robust than traditional PDMS microfluidic devices. The epoxy structure is resistant to swelling by many organic solvents, which opens new possibilities for experiments involving light organic liquids. Additionally, the surface wettability behavior of these devices is more stable than that of PDMS. The construction of optical adhesive microfluidic devices is simple, yet requires incrementally more effort than the making of PDMS-based devices. Also, though optical adhesive devices are stable in organic liquids, they may exhibit reduced bond-strength after a long time. Optical adhesive microfluidic devices can be made in geometries that act as 2-D micromodels for porous media. These devices are applied in the study of oil displacement to improve our understanding of the pore-scale mechanisms involved in enhanced oil recovery and aquifer remediation.

The goal of this procedure is to easily and rapidly produce a microfluidic device with customizable geometry and resistance to swelling by organic fluids for oil recovery studies. A polydimethylsiloxane mold is first generated, and then used to cast the epoxy-based device. A representative displacement study is reported.

Microfluidic devices are versatile tools for studying transport processes at a microscopic scale. A demand exists for microfluidic devices that are ...

Environment

Using Synchrotron Radiation Microtomography to Investigate Multi-scale Three-dimensional Microelectronic Packages

Synchrotron radiation micro-tomography (SR&#181;T) is a non-destructive three-dimensional (3D) imaging technique that offers high flux for fast data acquisition times with high spatial resolution. In the electronics industry there is serious interest in performing failure analysis on 3D microelectronic packages, many which contain multiple levels of high-density interconnections. Often in tomography there is a trade-off between image resolution and the volume of a sample that can be imaged. This inverse relationship limits the usefulness of conventional computed tomography (CT) systems since a microelectronic package is often large in cross sectional area 100-3,600 mm2, but has important features on the micron scale. The micro-tomography beamline at the Advanced Light Source (ALS), in Berkeley, CA USA, has a setup which is adaptable and can be tailored to a sample&#39;s properties, i.e., density, thickness, etc., with a maximum allowable cross-section of 36 x 36 mm. This setup also has the option of being either monochromatic in the energy range ~7-43 keV or operating with maximum flux in white light mode using a polychromatic beam. Presented here are details of the experimental steps taken to image an entire 16 x 16 mm system within a package, in order to obtain 3D images of the system with a spatial resolution of 8.7 &#181;m all within a scan time of less than 3 min. Also shown are results from packages scanned in different orientations and a sectioned package for higher resolution imaging. In contrast a conventional CT system would take hours to record data with potentially poorer resolution. Indeed, the ratio of field-of-view to throughput time is much higher when using the synchrotron radiation tomography setup. The description below of the experimental setup can be implemented and adapted for use with many other multi-materials.

For this study synchrotron radiation micro-tomography, a non-destructive three-dimensional imaging technique, is employed to investigate an entire microelectronic package with a cross-sectional area of 16 x 16 mm. Due to the synchrotron&#39;s high flux and brightness the sample was imaged in just 3 min&#160;with an 8.7 &#181;m spatial resolution.

Synchrotron radiation micro-tomography (SR&#181;T) is a non-destructive three-dimensional (3D) imaging technique that offers high flux for fast data ...

Protocol of Electrochemical Test and Characterization of Aprotic Li-O2 Battery

We demonstrate a method for electrochemical testing of an aprotic Li-O2 battery. An aprotic Li-O2 battery is made of a Li-metal anode, an aprotic electrolyte, and an O2-breathing cathode. The aprotic electrolyte is a solution of lithium salt with aprotic solvent; and porous carbon is commonly used as the cathode substrate. To improve the performance, an electrocatalyst is deposited onto the porous carbon substrate by certain deposition methods, such as atomic layer deposition (ALD) and wet-chemistry reaction. The as-prepared cathode materials are characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray absorption near edge structure (XANES). A Swagelok-type cell, sealed in a glass chamber filled with pure O2, is used for the electrochemical test on a battery test system. The cells are tested under either capacity-controlled mode or voltage controlled mode. The reaction products are investigated by electron microscopy, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy, and Raman spectroscopy to study the possible pathway of oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). This protocol demonstrates a systematic and efficient arrangement of routine tests of the aprotic Li-O2 battery, including the electrochemical test and characterization of battery materials.

Protocol of Electrochemical Test and Characterization of Aprotic Li-O2 Battery

A protocol for the electrochemical testing of an aprotic Li-O2 battery with the preparation of electrodes and electrolytes and an introduction of the frequently used methods of characterization is presented here.

We demonstrate a method for electrochemical testing of an aprotic Li-O2 battery. An aprotic Li-O2 battery is made of a Li-metal anode, an aprotic ...

Dynamic Pore-scale Reservoir-condition Imaging of Reaction in Carbonates Using Synchrotron Fast Tomography

Underground storage permanence is a major concern for carbon capture and storage. Pumping CO2 into carbonate reservoirs has the potential to dissolve geologic seals and allow CO2 to escape. However, the dissolution processes at reservoir conditions are poorly understood. Thus, time-resolved experiments are needed to observe and predict the nature and rate of dissolution at the pore scale. Synchrotron fast tomography is a method of taking high-resolution time-resolved images of complex pore structures much more quickly than traditional &#181;-CT. The Diamond Lightsource Pink Beam was used to dynamically image dissolution of limestone in the presence of CO2-saturated brine at reservoir conditions. 100 scans were taken at a 6.1 &#181;m resolution over a period of 2 hours. The images were segmented and the porosity and permeability were measured using image analysis and network extraction. Porosity increased uniformly along the length of the sample; however, the rate of increase of both porosity and permeability slowed at later times.

Synchrotron fast tomography was used to dynamically image dissolution of limestone in the presence of CO2-saturated brine at reservoir conditions. 100 scans were taken at a 6.1 &#181;m resolution over a period of 2 h.

Underground storage permanence is a major concern for carbon capture and storage. Pumping CO2 into carbonate reservoirs has the potential to dissolve ...

Applying X-ray Imaging Crystal Spectroscopy for Use as a High Temperature Plasma Diagnostic

X-ray spectra provide a wealth of information on high temperature plasmas; for example electron temperature and density can be inferred from line intensity ratios. By using a Johann spectrometer viewing the plasma, it is possible to construct profiles of plasma parameters such as density, temperature, and velocity with good spatial and time resolution. However, benchmarking atomic code modeling of X-ray spectra obtained from well-diagnosed laboratory plasmas is important to justify use of such spectra to determine plasma parameters when other independent diagnostics are not available. This manuscript presents the operation of the High Resolution X-ray Crystal Imaging Spectrometer with Spatial Resolution (HIREXSR), a high wavelength resolution spatially imaging X-ray spectrometer used to view hydrogen- and helium-like ions of medium atomic number elements in a tokamak plasma. In addition, this manuscript covers a laser blow-off system that can introduce such ions to the plasma with precise timing to allow for perturbative studies of transport in the plasma.

X-ray spectra provide a wealth of information on high temperature plasmas. This manuscript presents the operation of a high wavelength resolution spatially imaging X-ray spectrometer used to view hydrogen- and helium-like ions of medium atomic number elements in a tokamak plasma.

Pore-scale Imaging and Characterization of Hydrocarbon Reservoir Rock Wettability at Subsurface Conditions Using X-ray Microtomography

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