Techniques for image enhancement and segmentation of tomographic images of porous materials

Sheppard, Adrian; Sok, Robert; Averdunk, Holger

doi:10.1016/j.physa.2004.03.057

Cited by 367 publications

(233 citation statements)

References 19 publications

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“…The effective segmentation of the resulting images can be a real challenge with these systems, as the segmentation of images containing a partial saturation of multiple fluids is significantly more challenging that the segmentation of dry images, so the use of simple grey-scale universal thresholding is insufficient 51 . The use of watershed segmentation not only gives the most reliable results, compared to other algorithms in the literature, but is also the most effective at dealing with ring and partial volume artifacts…”

Section: Discussionmentioning

confidence: 99%

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

Andrew

Bijeljic

Blunt

2015

JoVE

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X-ray microtomography was used to image, at a resolution of 6.6 µm, 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 CO 2 storage. Chemical equilibrium between the CO 2 , 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 CO 2 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 CO 2 were trapped, with a residual saturation of 0.203 ± 0.013, and the sizes of larger volume ganglia obey power law distributions, consistent with percolation theory.

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Section: Discussionmentioning

confidence: 99%

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

Andrew

Bijeljic

Blunt

2015

JoVE

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“…Take Changqing sample for example, the first step is to reconstruct CQ-N1000-R1 from raw images, and typical image processing procedures are applied [45]. The other step is to change size and resolution to obtain structure such as CQ-N500-R0.25 from CQ-N1000-R1.…”

Section: Structure Reconstruction Proceduresmentioning

confidence: 99%

“…Base structure is reconstructed following typical image processing procedure, that is, pre-processing, image segmentation and post-processing [45,46]. In pre-processing part, brightness and contrast of the raw images are adjusted to make the images clearer, and median filter is used to smooth the images and reduce background noises.…”

Section: Structure Reconstruction Proceduresmentioning

confidence: 99%

Critical Resolution and Sample Size of Digital Rock Analysis for Unconventional Reservoirs

Liu

Wang

2018

Energies

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Digital rock analysis (DRA) has exhibited strong ability and significant potential to help people to image geological microstructures and understand transport mechanisms in rocks underground, especially for unconventional reservoirs like tight sandstone and shale. More and more new technologies have been developed for higher resolutions, which always come with higher expense. However, the balance between cost (money and time) and benefit has never been figured out quantitatively for these studies. As the cost and benefit are directly related to image resolution and size, this work is focusing on whether there is a critical resolution and sample size when using DRA for accurate enough predictions of rock properties. By numerically changing the digital resolutions of the reconstructed structures from high-resolution micro-computed tomography (CT) scanned tight rock samples, it is found that the permeability predictions get stable when the resolution is higher than a cut-off resolution (COR). Different from physical rocks, the representative element volume (REV) of a digital rock is influenced by the digital resolution. The results of pore-scale modeling indicate that once sample size is larger than the critical sample size and the scan resolution higher than the critical resolution for a given rock, the predicted rock properties by DRA are accurate and representative.

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“…The resulting images obtained from the CT scanning process are not sharp enough and can present significant light scattering and noise. These issues are corrected prior to segmentation by applying image intensity adjustments (to enhance contrast), unsharp masking (sharpens the edges) (Sheppard et al 2004), and 2-D median filtering (to reduce noise). Due to the nature of the images, it has been noticed that careful selection of the image adjustment parameters is necessary, since it can greatly affect the final outcome of the volume rendering procedure.…”

Section: Image Processingmentioning

confidence: 99%

Pore-Scale Numerical Investigation of Pressure Drop Behaviour Across Open-Cell Metal Foams

et al. 2017

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The development and validation of a grid-based pore-scale numerical modelling methodology applied to five different commercial metal foam samples is described. The 3-D digital representation of the foam geometry was obtained by the use of X-ray microcomputer tomography scans, and macroscopic properties such as porosity, specific surface and pore size distribution are directly calculated from tomographic data. Pressure drop measurements were performed on all the samples under a wide range of flow velocities, with focus on the turbulent flow regime. Airflow pore-scale simulations were carried out solving the continuity and Navier-Stokes equations using a commercial finite volume code. The feasibility of using Reynolds-averaged Navier-Stokes models to account for the turbulence within the pore space was evaluated. Macroscopic transport quantities are calculated from the pore-scale simulations by averaging. Permeability and Forchheimer coefficient values are obtained from the pressure gradient data for both experiments and simulations and used for validation. Results have shown that viscous losses are practically negligible under the conditions investigated and pressure losses are dominated by inertial effects. Simulations performed on samples with varying thickness in the flow direction showed the pressure gradient to be affected by the sample thickness. However, as the thickness increased, the pressure gradient tended towards an asymptotic value.

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Techniques for image enhancement and segmentation of tomographic images of porous materials

Cited by 367 publications

References 19 publications

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

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

Critical Resolution and Sample Size of Digital Rock Analysis for Unconventional Reservoirs

Pore-Scale Numerical Investigation of Pressure Drop Behaviour Across Open-Cell Metal Foams

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