Brady Flinchum

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Brady Flinchum
Brady-Flinchum.jpg
BSc Geophysics
BSc university University of Nevada Reno

Brady Flinchum has always been a curious and enthusiastic individual who loves physics and mathematics. When he discovered the University of Nevada Reno (UNR) offered a geophysics degree, a subject that applied physics and mathematics to understand the Earth, he enthusiastically selected that as a major and never looked back. In 2011, the summer before graduation, Brady was selected as an Incorporated Research Institutions for Seismology (IRIS) intern. He studied slow slip earthquakes along the Cascadia Subduction Zone. Upon his return to UNR at the end of summer, Brady began working on a research project simulating earthquakes and the ground motion response of the Las Vegas basin, which led to his first publication. In 2012, Brady graduated with a B.S. degree in geophysics and accepted employment by Multi-Phase Technologies (MPT) as a staff geophysicist. He worked on a variety of projects including using electrical resistivity to locate abandoned mine tunnels and monitoring heat sources between two wells using time-lapse resistivity measurements.

Brady left MPT to pursue his Ph.D. at the University of Wyoming. He is currently in his third year and part of the Wyoming Center for Environmental Hydrology and Geophysics (WyCEHG). Brady is interested in using near-surface geophysical methods as an imaging tool to provide new and unique perspectives of the subsurface that will improve our understanding of hydrologic systems, ecosystems, weathering, and erosional processes in the top 10 to 100 meters of the Earth’s subsurface. Furthermore, he is interested in improving the ability to estimate the spatial distribution of parameters influencing groundwater flow and storage, specifically porosity. Brady is trying to exploit the sensitivity of seismic velocities in the vadose zone and surface nuclear magnetic resonance’s unique ability to determine pore scale properties in the saturated zone to provide spatially exhaustive estimates of porosity. Currently, Brady is working with an extensive geophysical data set comprised of 25 seismic refraction profiles, 27 electrical resistivity lines, and 5 surface nuclear magnetic resonance soundings in a granite catchment in the Laramie Range, Wyoming. He is using these data, in combination with borehole data, to image subsurface structure, characterize preferential flow paths, and estimate porosity on large scales (hundreds of meters).

2016 Near Surface Research Award Recipient

Abstract

Fresh water, or the lack of it, impacts almost every environment on Earth—its availability governs ecosystems, influences human activity, and sculpts landscapes. Groundwater is a significant piece of the fresh water reservoir and in this project, I focus on improving the ability to estimate the spatial distribution of parameters influencing groundwater flow and storage, specifically porosity. Although a unique porosity exists in the subsurface, it is difficult to characterize lateral distributions of porosity at depths greater than a few meters. In an attempt to provide porosity estimates across large spatial scales (hundreds of meters) in the saturated and unsaturated zones, I will rely on non-invasive geophysical measurements—but estimates of porosity from different geophysical measurements do not always agree. I compare seismically estimated porosities using a 2D rock physics Bayesian inversion to estimates from surface nuclear magnetic resonance (NMR) on a sandstone and a fractured granite aquifer. The seismically estimated porosities were 5 times higher in the granite aquifer and 3 times lower in the sandstone aquifer (Flinchum et al., 2015). In this study, I seek to understand why seismically estimated porosities are different than NMR-derived porosities—can the difference provide additional information about the aquifer? I hypothesize the difference between the two measurements can be used to differentiate between shallow confined and unconfined aquifers because confining pressure affects seismically estimated porosities but will not affect surface NMR estimates.

To address this hypothesis, I propose a combined geophysical approach using P- and S-wave velocities and surface NMR data ground-truthed by lab measurements conducted on samples. The seismic data will be used to estimate porosity in the unsaturated zone and the surface NMR data will constrain estimates in the saturated zone. I will collect geophysical data on two geologically distinct sites: a confined sandstone aquifer and an unconfined weathered and fractured granite aquifer. To collect samples, I will use a geoprobe and a backpack drill and measure porosities in the laboratory by drying and weighing known sample volumes. To obtain porosities at depths greater than the geoprobe can sample, I will utilize existing boreholes and a downhole NMR logging system. Using this unique data set, I will be able to estimate unsaturated and saturated porosity over large spatial scales and improve our ability to characterize shallow groundwater aquifers. The results of this project will improve the understanding of the relationship between hydrophysical properties and near-surface geophysical parameters on different lithologies and at large spatial scales. Currently, we have access and resources to run the required geophysical equipment and only require funding for labor, operations, and materials pertaining to the geoprobe data acquisition.

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Brady Flinchum
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