PERM Inc.’s Tomographic Imaging & Porous Media Laboratory is one of the largest tomographic facilities in North America which is focused on CT Scanning Core and Laboratory Experiments for the Oil & Gas Industry.

This is an example of an axial CT scan slice through full diameter core. It is colourized for density. Both density and porosity can be accurately derived from core with CT Scanners.

• CT Scanners use an x-ray source and pass x-rays through the object being scanned to a detector on the other side.
• We can obtain 1-D projections of X-Ray attenuation at different angles; When just one angle is scanned it is like a regular chest x-ray.
• Numerical algorithms construct a 2-D cross-section of the object from all the 1-D projections and allow you to see inside the object.
  • X-ray attenuation is proportional to density, so CT effectively gives a 2-D density cross-section of the sample.
  • We can derive porosity from the images.
  • This is very accurate quantitative data.
• Scanning is 100% non-intrusive.
• PERM Inc. can scan full diameter cores (3″ to 4″+) in core tubes or coreholders.
• The core can be frozen (native state) OR at reservoir temperature and pressure.
• PERM Inc. can scan many other types of laboratory experiments to gain visualization and further understanding.
• Resolution = 400 um x 400 um x thickness of the slice (usually 1-3 mm)

1. Scout Scans (Longitudinal) 1-D projections
2. Axial Scans (Cross Sectional) 2-D projections

CT Scout Scan of Core while core is still in the tubes, at 0° and 90°.

CT Scanning Core in Core Tubes to Identify Core Recovery

CT Axial Scans allow us to see inside the core and find fractures or potential flow blockages.

From each image or axial slice (typically 1-3 mm thick) we get quantitative data for density and porosity of the core.

With enough axial scans, you can generate a density and porosity log that has a very high resolution. These can be calibrated against downhole logs. The resolution can be as low as one axial image every 4 cm or as high as one axial image every 1 mm.

While CT Scanning gives a precise density of a core, if it is an unconsolidated core, then density may appear lower due to the absence of overburden pressure. As a result, for an unconsolidated core, the density may not match the logs precisely. In this circumstance, we can apply a correction to account for the reservoir pressure in order to match the logs. An alternative to this would be to take the core and put it in a coreholder and CT Scan while the core is under pressure.

For unconsolidated core (such as oilsand), it is important to check for artificial fractures created during coring. In the example above, we scanned an oilsand core at reservoir pressure (in a core tube) to see the initial state of the core prior to flooding. We found many artificial fractures and the density did not match log density. A very mild pressure cycling procedure was utilized to heal the fractures and then we re-scanned the core for verification. The result was core that had all artificial fractures removed and a density that matched the downhole log. The sample is then prepared to begin the coreflood and/or SCAL tests. This is an important step to take if you do not wish to flow through artificial fractures and get incorrect results.

CT Scan during a coreflood to add visualization and help understand and interpret the test results.

Identify how the different types of rock in your reservoir will affect oil recovery.

The above example was a vertical EOR coreflood; CT Scanning was used to determine end capillary effects at the bottom of the core. The oil saturation at the bottom was much higher due to these end capillary effects, which can lead one to expect lower oil recovery from the core test. Since we could tell where the oil was, we can take that into account when determining overall recovery factors that would be expected in the field.

This is an example of porosity distribution for a carbonate core.

Some reservoirs are difficult to quantify “pay” versus other non-pay zones when everything is mixed and interbed. Mineralogical mapping was done with density data to figure out net pay in this mixed dolomite/shale reservoir.

Further analysis can be conducted on unconventional reservoirs to help with core characterization. This is one core tube that was scanned every one mm and then digitally reconstructed; it was then digitally slabbed. Beside the digital slab image, is the density and porosity log.

Bulk mineralogical data can be derived for some core by conducting dual energy CT Scanning on the core.

This example shows a density and porosity log, beside a Scout Scan at 0° and 90°. Beside that is a reconstruction of 1500 axial slices that have been digitally slabbed to see inside the core. Also included, is every 15th axial slice in greyscale along with the same axial images colourized for density.

If you take enough Axial CT Scan Images side by side, every ~1 mm, then you can do a reconstruction and see inside the core as well. A tremendous amount of detail is available.