EAST TENNESSEE GEOLOGICAL SOCIETY
  MAY 2018


Monday, May 14, 2018
6:00 - 7:30 pm

Pellissippi State Technical Community College
10915 Hardin Valley Road, Knoxville
J.L Goins Administration Building
Faculty/Staff Dining Room

MAY PRESENTATION

Award Winning Student Presentations

Inverse Estimation of Surface Fractal Dimension and Aperture Width for Rock Fracture
from Spontaneous Imbibition Measurements

Presented By
Jared W. Brabazon, MS Candidate
Department of Earth and Planetary Sciences
University of Tennessee, Knoxville, Tennessee
(Co-authors include E. Perfect, C. L. Cheng, H.Z. Bilheux, A.S. Tremsin, and L.J. Santodonato)

Abstract

Spontaneous imbibition is a capillary-driven flow process, in which a wetting fluid moves into a porous medium displacing a preexisting non-wetting fluid. The phenomenon has been shown to be markedly faster in fractured porous media than in the surrounding matrix. Differences in fracture imbibition rates are influenced by the fracture width and overall roughness of the fracture surface. Fractal dimensions are an excellent way to characterize surface roughness across multiple scales. In the present study, we derive a theoretical model for early-time spontaneous imbibition (i.e., ignoring gravity) of a wetting fluid that allows for the inverse estimation of fracture surface fractal dimensions and mean aperture widths. The model was tested using previously published data for the spontaneous imbibition of water into four initially dry fractured Berea sandstone cores of varying permeability. The data were collected using dynamic neutron radiography at ORNL’s Neutron Imaging Facility (beam line CG-1D, HFIR). The theoretical model was fitted to the experimental data using non-linear least squares regression. Analyses for three of the four cores investigated yielded surface fractal dimensions with values between two and three, providing plausible characterization of multi-scale fracture surface roughness. The estimated mean fracture aperture widths compared favorably with independent measurements from image analysis. The proposed model is physically-based and could be useful in applications as diverse as the deep disposal of hazardous wastes and assessing caprock integrity. Future research should focus on forwardly predicting spontaneous imbibition through independent measurements of the fractal dimension. Forward prediction of this model has potential to help reduce leak-off in hydraulic fracturing operations as well as increase oil and gas recovery.

Biography

Research of Jared Brabazon focuses on the hydraulic properties of fractured low-porosity rocks. In particular, Jared is focusing on measuring and modeling spontaneous imbibition, a capillary-driven flow process, of water into fractured granite, limestone, sandstone, and shale. His research can be applied to applications such as deep disposal of waste, caprock integrity, and leak-off in hydraulic fracturing. While research is at the forefront of his life, he can also be found rock climbing with his wife, backpacking, kayaking, or enjoying geology on a hike. He has played both guitar and saxophone for over 10 years and enjoys the occasional music recording session.


Volatile Characterization on Near Earth Asteroids

Presented By
Lauren E. McGraw, PhD Candidate
Department of Earth and Planetary Sciences
University of Tennessee, Knoxville, Tennessee
(Co-authors include J. P. Emery, C. A. Thomas, A. R. Rivkin, and N. R. Wigton)

Abstract

Near Earth Asteroids (NEAs) are excellent laboratories for processes that affect the surfaces of airless bodies. Most NEAs are not expected to contain surface volatiles such as OH/H2O since they formed in the anhydrous regions of the solar system and since their surface temperatures are high enough to evaporate such volatiles. However, OH/H2O has been discovered on other seemingly dry bodies in the inner solar system, such as the Moon and Vesta. Possible sources for OH/H2O on these bodies include carbonaceous chondrite impacts and interactions with protons implanted by solar wind. NEAs should be subjected to the same processes as other “dry” bodies in the inner solar system so are hypothesized to also contain OH/H2O on their surfaces.

We observed NEAs using SpeX on NASA’s Infrared Telescope Facility on Mauna Kea, Hawaii. Spectra were collected using both prism (0.7-2.52 Ám) and LXD_short (1.67-4.2 Ám) modes in order to accurately characterize asteroid type and the 3-Ám region, where the OH/H2O signature is present.

We have made 28 observations of 20 NEAs as part of this ongoing project, with three more observations scheduled for this Summer
1. Of those, at least 3 NEAs exhibit an absorption feature in the 3-Ám region: (433) Eros, (1036) Ganymed, and (3122) Florence. All three have both been observed multiple times and by multiple observers (e.g., Wigton, 2015; Rivkin et al. 2017), including two observations of Eros in Fall 2016, and one observation of Florence in September 2017. Of the other 17 NEAs studied, eight do not exhibit a 3-Ám spectral feature, two are inconclusive, and the rest have not yet been processed.

Characterizing the shape of the 3-Ám absorption feature can yield information on the source of the OH/H2O on the surface. Shallow features that gradually slope upward towards the continuum, such as is present in the spectra of Eros and Ganymed, indicate the presence of OH, which is inferred to have formed due to solar wind proton bombardment. Further study of these objects will shed more light on how volatiles are brought to the surface of “dry” NEAs.

1Four observations are scheduled to occur between the writing of this abstract and the presentation date, so these numbers may change if observations are not successful.

Biography

Lauren McGraw is finishing her second year as a PhD student at the University of Tennessee. She received with honors her B. S. degree in geology from the University of Oklahoma with minors in math, chemistry, and meteorology. Lauren graduated Summa Cum Laude and was recognized as the Outstanding Senior for the College of Earth and Energy. She now works with Josh Emery studying near-Earth Asteroids (NEAs). Research focuses on studying the 3-Ám spectral region using telescopic observations to characterize volatiles on NEAs. To date, she has logged over 60 hours on NASA’s Infrared Telescope Facility for this project. Lauren is also a graduate research assistant to Josh for the OSIRIS-REx asteroid sample return mission, which is scheduled to reach the NEA Bennu this Fall.


Constraining the Origin of Jupiter’s Trojan Asteroids

Presented By
Audrey C. Martin, PhD Candidate
Department of Earth and Planetary Sciences
University of Tennessee, Knoxville, Tennessee

Abstract

Determining the origin of asteroids provides an effective means of constraining the solar system’s dynamic past. Jupiter Trojan asteroids (hereafter Trojans) may help in determining the amount of radial mixing that occurred during giant planet migration. Previous studies aimed at characterizing surface composition show that Trojans have low albedo surfaces and are spectrally featureless in the near infrared. The thermal infrared (TIR) wavelength range has advantages for detecting silicates on low albedo asteroids such as Trojans. The 10 ?m region exhibits strong features due to the Si-O fundamental molecular vibrations. Silicates that formed in the inner solar system tend to be crystalline and Mg-rich, whereas silicates that accreted in the outer solar system are more likely to be in an amorphous phase and Fe-rich. We hypothesize that the Trojans formed in the outer solar system (i.e., the Kuiper Belt), and therefore will have a more dominant amorphous and Fe-rich spectral silicate component. With TIR spectra from the Spitzer Space Telescope, we identify mineralogical features from the surface of 11 Trojan asteroids. Fine-grain mixtures of crystalline pyroxene and olivine exhibit a 10 ?m feature with sharp cutoffs between about 9 ?m and 12 ?m, which create a broad flat plateau. Amorphous phases, when present, smooth the sharp emission features, resulting in a dome-like shape. Emissivity peaks associated with olivine and pyroxene shift from shorter to longer wavelengths with decreasing Mg/(Mg+Fe). Preliminary results indicate that the surface of analyzed Trojans contain primarily amorphous silicates. Emissivity spectra of asteroids 1986 WD and 4709 Ennomos include small peaks in the 10 ?m region, diagnostic of small amounts of crystalline pyroxene. The general abundance of amorphous silicates on the surface of Trojans suggest formation beyond their current position at 5.2 AU. One explanation is that Trojans formed in the same region as Kuiper Belt objects, and when giant planet migration ensued, they were swept into Jupiter’s stable Lagrange points where they are found today. As such, it is possible that an ancestral group of Kuiper Belt objects were separated from Trojans during large planet migration.

Biography

Originally, Audrey went to college to study theatre, but found herself intrigued by the natural world. She ended up graduating from Saint Louis University with a B.S. in physics and minors in Mathematics and Geology. After undergrad, Audrey decided to study planetary science at the University of Tennessee, where she is now perusing a PhD by studying a population of small bodies called Trojan asteroids.

Most asteroids in the inner Solar System are found in the Main Asteroid Belt, however Trojans are found slightly further out in Jupiter’s stable Lagrange points. They have gravitationally stable orbits around the Sun, and probably haven’t moved for nearly 4.5 billion years. Trojan asteroids are ‘primitive bodies’ and hold useful information about the environment in the early solar system. I study Trojan asteroids to understand major events that shaped our solar system.


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