Pavel Iassonov

Bio: Pavel Iassonov is an academic researcher from University of Arizona. The author has contributed to research in topics: Tomography & Image segmentation. The author has an hindex of 3, co-authored 3 publications receiving 484 citations.

Segmentation of X‐ray computed tomography images of porous materials: A crucial step for characterization and quantitative analysis of pore structures

Abstract: [1] Nondestructive imaging methods such as X-ray computed tomography (CT) yield high-resolution, three-dimensional representations of pore space and fluid distribution within porous materials. Steadily increasing computational capabilities and easier access to X-ray CT facilities have contributed to a recent surge in microporous media research with objectives ranging from theoretical aspects of fluid and interfacial dynamics at the pore scale to practical applications such as dense nonaqueous phase liquid transport and dissolution. In recent years, significant efforts and resources have been devoted to improve CT technology, microscale analysis, and fluid dynamics simulations. However, the development of adequate image segmentation methods for conversion of gray scale CT volumes into a discrete form that permits quantitative characterization of pore space features and subsequent modeling of liquid distribution and flow processes seems to lag. In this paper we investigated the applicability of various thresholding and locally adaptive segmentation techniques for industrial and synchrotron X-ray CT images of natural and artificial porous media. A comparison between directly measured and image-derived porosities clearly demonstrates that the application of different segmentation methods as well as associated operator biases yield vastly differing results. This illustrates the importance of the segmentation step for quantitative pore space analysis and fluid dynamics modeling. Only a few of the tested methods showed promise for both industrial and synchrotron tomography. Utilization of local image information such as spatial correlation as well as the application of locally adaptive techniques yielded significantly better results.

Application of Segmentation for Correction of Intensity Bias in X-Ray Computed Tomography Images

Abstract: Nondestructive imaging methods such as x-ray computed tomography (CT) yield high-resolution, grayscale, three-dimensional visualizations of pore structures and fluid interfaces in porous media. To separate solid and fluid phases for quantitative analysis and fluid dynamics modeling, segmentation is applied to convert grayscale CT volumes to discrete representations of media pore space. Unfortunately, x-ray CT is not free of artifacts, which complicates segmentation and quantitative image analysis due to obscuration of significant features or misinterpretation of attenuation values of a single material in different image sections. Images or volumes emanating from polychromatic (industrial) scanners are especially prone to high noise levels, beam hardening, scattered x-rays, or ring artifacts. These problems can be alleviated to a certain extent through application of metal filters, careful detector calibration, and sample centering, but they cannot be completely avoided. We have developed a simple three-dimensional approach to numerically correct for image artifacts using sequential segmentation. This procedure leads to a significant improvement of grayscale data as well as final segmentation results with reasonable computational demand.

Two-dimensional finite-difference model of seafloor compliance

Abstract: SUMMARY Seafloor compliance is the measure of seafloor deformation under a pressure signal. Our new 2-D finite-difference compliance modelling algorithm presents several advantages over the existing compliance models, including the ability to handle any gridded subsurface structure with no limitations on the gradients of the material properties, as well as significantly improved performance. Applying this method to some of the problems inaccessible to previously existing methods, demonstrates that lateral variations in subsurface structure must be accounted for to adequately interpret compliance data. In areas with significant lateral variations, the utilization of 1-D modelling and inversion is likely to result in high interpretation errors, even when additional subsurface structure information is available. We find that flattened pure melt bodies have a significantly higher compliance than cylindrical melt bodies with the same cross-sectional area. The compliance created by such bodies often has side peaks over their edges, which are as strong as or stronger than the central peak, requiring a series of measurements to best constrain their size and shear velocity. Finally, we find that the compliance data are far and away most sensitive to the broad, thick, lower-crustal partial melt zone. Our simple data fitting model for the compliance measurements on the East Pacific Rise at 9°48′N required shear velocities as low as 700 m s−1 in the centre of this zone, far below the values previously estimated using 1-D model based inversions, suggesting higher melt percentages than those previously estimated, while small melt bodies in the upper part of the crust were found to have little or no effect on the measured compliance.

Characterization and Analysis of Porosity and Pore Structures

Abstract: Porosity plays a clearly important role in geology. It controls fluid storage in aquifers, oil and gas fields and geothermal systems, and the extent and connectivity of the pore structure control fluid flow and transport through geological formations, as well as the relationship between the properties of individual minerals and the bulk properties of the rock. In order to quantify the relationships between porosity, storage, transport and rock properties, however, the pore structure must be measured and quantitatively described. The overall importance of porosity, at least with respect to the use of rocks as building stone was recognized by TS Hunt in his “Chemical and Geological Essays” (1875, reviewed by JD Dana 1875) who noted: > “Other things being equal, it may properly be said that the value of a stone for building purposes is inversely as its porosity or absorbing power.” In a Geological Survey report prepared for the U.S. Atomic Energy Commission, Manger (1963) summarized porosity and bulk density measurements for sedimentary rocks. He tabulated more than 900 items of porosity and bulk density data for sedimentary rocks with up to 2,109 porosity determinations per item. Amongst these he summarized several early studies, including those of Schwarz (1870–1871), Cook (1878), Wheeler (1896), Buckley (1898), Gary (1898), Moore (1904), Fuller (1906), Sorby (1908), Hirschwald (1912), Grubenmann et al. (1915), and Kessler (1919), many of which were concerned with rocks and clays of commercial utility. There have, of course, been many more such determinations since that time. There are a large number of methods for quantifying porosity, and an increasingly complex idea of what it means to do so. Manger (1963) listed the techniques by which the porosity determinations he summarized were made. He separated these into seven methods for …