Estimating properties from millimetric sized rock cuttings using micro computed tomography (CT)

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Author(s): Goldfarb, Eric J.; Ikeda, Ken; Ketcham, Richard A.; Tisato, Nicola
Author Affiliation(s): Primary:
University of Texas at Austin, Austin, TX, United States
Volume Title: AGU 2018 fall meeting
Source: American Geophysical Union Fall Meeting, Vol.2018; American Geophysical Union 2018 fall meeting, Washington, DC, Dec. 10-14, 2018. Publisher: American Geophysical Union, Washington, DC, United States
Note: In English
Summary: Properties obtained from physical rock samples are necessary for calibrating accurate subsurface models. Models of rock type, porosity, density and elastic wave velocities are useful for civil, mining, and petrophysical engineers; hydrogeologists and municipal planners; and scientists (e.g. IODP). Cylindrical samples tens of centimeters in size are typically required to measure these properties in the laboratory. Collecting in situ samples such as drill cores is important for understanding how rock properties change with depth; however, this is extremely expensive, and rarely done. Drilling is generally common, but rare for the purpose of collecting cores. Byproducts of all drilling activities include rock cuttings, which are millimetric sized pieces of the rock that break off and are brought to the surface in the drilling mud. Like cores, these cuttings come from in situ conditions. However, their small sizes and irregular shapes make them hard to test for elastic properties in the lab. Nevertheless, advances in micro-computed tomography offer new opportunities to digitally characterize such samples. In the laboratory, we measured rock properties of a Berea sandstone core and then used micro-computed tomography to estimate rock properties on millimetric sized pieces of that core comparable to drill cuttings. To create our three-dimensional rock model we used the "targeted method" that does not involve segmentation. By scanning the sample along with phantoms of known density (air, two types of glass, and quartz), an empirical curve is created and used to convert X-ray attenuation to density for each voxel. Porosity is then estimated from its inverse relationship to density. An effective medium theory is used to translate the 3D distribution of porosity into elastic properties. Finally, we numerically simulated the same tests that we performed on the laboratory core. Elastic wave velocities, density, and porosity results from individual cuttings are accurate within 10% from the laboratory-measured core. When averaging multiple cuttings, the results converge to within 5% of the laboratory core values. This suggests that at first order, scanning many cuttings can provide an analogue for an equivalent core.
Year of Publication: 2018
Research Program: IODP2 International Ocean Discovery Program
Key Words: 15 Miscellaneous and Mathematical Geology; Civil engineering; Computed tomography; International Ocean Discovery Program; Tomography
Record ID: 2019061705
Copyright Information: GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data supplied by, and/or abstract, Copyright, American Geophysical Union, Washington, DC, United States

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