Browsing by Author "Fahrman, Benjamin Paul"

Now showing 1 - 2 of 2
  • Thumbnail Image
    Geophone Array Optimization for Monitoring Geologic Carbon Sequestration using Double-Difference Tomography
    Fahrman, Benjamin Paul (Virginia Tech, 2011-12-05)
    Analysis of synthetic data was performed to determine the most cost-effective tomographic monitoring system for a geologic carbon sequestration injection site. Artificial velocity models were created that accounted for the expected velocity decrease due to the existence of a CO₂ plume after underground injection into a depleted petroleum reservoir. Seismic events were created to represent induced seismicity from injection, and five different geophone arrays were created to monitor this artificial seismicity. Double-difference tomographic inversion was performed on 125 synthetic data sets: five stages of CO₂ plume growth, five seismic event regions, and five geophone arrays. Each resulting velocity model from tomoDD—the double-difference tomography program used for inversion—was compared quantitatively to its respective synthetic velocity model to determine an accuracy value. The quantitative results were examined in an attempt to determine a relationship between cost and accuracy in monitoring, verification, and accounting applications using double-difference tomography. While all scenarios resulted in little error, no such relationship could be found. The lack of a relationship between cost and error is most likely due to error inherent to the travel time calculation algorithm used.
  • Thumbnail Image
    Numerical Modeling of Room-and-Pillar Coal Mine Ground Response
    Fahrman, Benjamin Paul (Virginia Tech, 2016-03-28)
    Underground coal mine ground control persists as a unique challenge in rock mass engineering. Fall of roof and rib continue to present a hazard to underground personnel. Stability of underground openings is a prerequisite for successful underground coal mine workings. An adaptation of a civil engineering design standard for analyzing the stability of underground excavations for mining geometries is given here. The ground response curve--developed over seventy years ago for assessing tunnel stability--has significant implications for the design of underground excavations, but has seen little use in complex mining applications. The interaction between the small scale (pillar stress-strain) and the large scale (ground response curve) is studied. Further analysis between these two length scales is conducted to estimate the stress on pillars in a room-and-pillar coal mine. These studies are performed in FLAC3D by implementing a two-scale, two-step approach. This two-scale approach allows for the interaction between the small, pillar scale and the large, panel scale to be studied in a computationally efficient manner.