A1 Journal article (refereed), original research

Statistical methods to enable practical on-site tomographic imaging of whole-core samples


Publication Details
Authors: Mendoza Alberto, Roininen Lassi, Girolami Mark, Heikkinen Jere, Haario Heikki
Publisher: Society of Exploration Geophysicists
Publication year: 2019
Language: English
Related Journal or Series Information: Geophysics
ISSN: 0016-8033
eISSN: 1942-2156
JUFO-Level of this publication: 1
Open Access: Not an Open Access publication

Abstract
Statistical
methods enable the use of portable industrial scanners with sparse
measurements, suitable for fast on-site whole-core X-ray computerized
tomography (CT), as opposed to conventional (medical) devices that use
dense measurements. This approach accelerates an informed first-stage
general assessment of core samples. To that end, this novel industrial
tomographic measurement principle is feasible for rock sample imaging,
in conjunction with suitable forms of priors in Bayesian inversion
algorithms. Gaussian, Cauchy, and Total Variation (TV) priors yield
different inversion characteristics for similar material combinations.
An evaluation of the inversion performance in rock samples considers, in
discrete form, conditional mean (CM) estimators, via Markov Chain Monte
Carlo (MCMC) algorithms with noise-contaminated measurements.
Additionally, further assessment shows that this statistical approach
better characterizes the attenuation contrast of rock materials,
compared to simultaneous reconstruction techniques (SIRT). Benchmarking
includes X-ray CT from numerical simulations of synthetic and
measurement-based whole-core samples. To this end, we consider
tomographic measurements of fine- to medium-grained sandstone core
samples, with igneous-rich pebbles from the Miocene, off the Shimokita
Peninsula in Japan, and fractured welded tuff from Big Bend National
Park, Texas. Bayesian inversion results confirm that with only 16
radiograms, natural fractures with aperture of less than 2mm wide are
detectable. Additionally, reconstructed images show approximately
spherical concretions of 6mm diameter. To achieve similar results,
filtered back projection (FBP) techniques require hundreds of
radiograms, only possible with conventional laboratory scanners.

Last updated on 2019-25-01 at 09:29