Statistical Methods To Enable Practical On-Site Tomographic Imaging of Whole-Core Samples
- Alberto Mendoza (Imperial College London) | Lassi Roininen (University of Oulu) | Mark Girolami (Imperial College London) | Jere Heikkinen (Finnos) | Heikki Haario (Lappeenranta University of Technology)
- Document ID
- Society of Petrophysicists and Well-Log Analysts
- SPWLA 59th Annual Logging Symposium, 2-6 June, London, UK
- Publication Date
- Document Type
- Conference Paper
- 2018. held jointly by the Society of Petrophysicists and Well Log Analysts (SPWLA) and the submitting authors.
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We show that 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 (with dense measurements). This approach accelerates an informed first-stage general assessment of core samples. To that end, we show that this novel industrial tomographic measurement principle is feasible for rock sample imaging, in conjunction with suitable forms of priors in Bayesian inversion algorithms. We assess the performance of the inversion with Gaussian, Cauchy, and Total Variation (TV) priors. In so doing, we consider, in discrete form, conditional mean (CM) estimators, via Markov Chain Monte Carlo (MCMC) algorithms with noise-contaminated measurements.
To benchmark the reliability of whole-core imaging with sparse radiograms via Bayesian inversion, in our study we include X-ray CT from numerical simulations of synthetic and measurement-based whole-core samples. To that 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 show that with only 16 radiograms, natural fractures with aperture of less than 2mm wide are detectable. Additionally, images show approximately spherical concretions of 6mm diameter. We show that to achieve similar results, filtered back projection (FBP) techniques require hundreds of radiograms, only possible with conventional (medical) laboratory scanners.
This paper shows that Bayesian inversion on whole-core X-ray CT is capable of imaging coarse sedimentary features that, with faster, simplified measurement principles, would aid in more efficient operational petrophysical decisions for planning further core analysis.
In evaluation of oil and gas reservoirs, one function of X-ray CT is to allow non-destructive initial examination of the internal structure of conventional whole-core (Varhaugh & Smithson 2015), and it is a valuable technique in efficiently selecting sub-samples for further analysis. Additionally, whole-core tomographic imaging is an effective tool for stratigraphy characterization, categorizing geological horizons, visualizing coarse sedimentary features, and core-log correlation (Inagaki et al. 2013, 2016, Kuras et al. 2016). Crain (2017) describes X-ray computed tomography as the current technology for “whole-core inspection at the macro level, core-log correlation, and plug sample characterization” across the oil and gas industry.
|File Size||8 MB||Number of Pages||17|