• Metal-insulator-metal diodes towards THz and optical energy harvesting: development of materials design principles

      O'Hayre, Ryan P.; Ginley, D. S. (David S.); Periasamy, Prakash; Parilla, Philip A.; Berry, Joseph J.; Ohno, Timothy R.; Knauss, Daniel M.; Furtak, Thomas E. (Thomas Elton), 1949- (Colorado School of Mines. Arthur Lakes Library, 2012)
      Metal-Insulator-Metal (MIM) structures are attractive candidates for high-frequency rectification applications such as THz imaging and sensors, and infrared/visible energy harvesting (rectenna) devices. This thesis develops materials selection principles to guide the choice of material pairs for MIM stacks with desired rectification performance. In particular, a first-of-its kind MIM materials space map is developed that correlates materials properties to rectification performance for different MIM combinations. The materials space diagram is generated based on systematic experimental studies that explore the role of both the metals and the insulator in the MIM stack in determining MIM device performance by evaluating the current-voltage response of a combinatorial set of MIM materials at low frequencies. A novel modified point-contact geometry is developed to rapidly examine a number of MIM material combinations. Material properties such as work function (Phi M) of the metals and electron affinity(Chi) of the insulator, as well as the thermodynamic chemical stability of the interface are identified as crucial elements for MIM materials selection. Investigations performed to identify the role of metals revealed that it is sufficient to choose the metals such that their [Delta Phi] is greater than ~ 300 meV to achieve desired rectification characteristics (high asymmetry and nonlinearity). Using the Nb/Nb2O5 bilayer as the model system, the asymmetry and the nonlinearity were found to be only weakly dependent [Delta Phi] above ~ 0.4 eV. A hypothesis is developed and tested that guides the insulator selection criteria. The proposed hypothesis states that, "to minimize the turn-on voltage and maximize asymmetry and nonlinearity, the electron affinity of the insulator should be close to one of the metal work function values so as to produce a low barrier height". Although the study validated the hypothesis across the material systems studied, preliminary experiments on two additional high potential MIM systems (Hf/TiO2/Pt and Sm/ZrOx/Pt) unexpectedly yielded much lower asymmetry and nonlinearity than predicted by the hypothesis. Thermodynamic and TEM cross-sectional analysis on these systems (Hf/TiO2 and Sm/ZrO2) revealed a critical observation that these interfaces are reactive even at RT and result in an interfacial compound (~ 3 nm thick). It is speculated that this reaction layer adversely influences the rectification performance. Thus it is proposed that in addition to choosing the materials based on their work function and electron affinity it is important to consider the thermodynamic stability of these interfaces as well. Band-offsets (electronic barrier height) at metal/insulator interfaces are measured via x-ray photoelectron spectroscopy (XPS). Band-diagrams constructed using the band-offset values agree well with their I-V response, verifying the proposed material design criteria. Measured electronic barrier height values are 0.1 (Nb2O5/Nb), 0 (Nb2O5/Ti), 0.6 (Nb2O5/Cu) and 0.6 eV(Nb2O5/Pt).
    • Examination of solute transport in highly heterogeneous media at the Macrodispersion Experiment (MADE) Site, Columbus, MS

      Benson, David A.; Stumb, Morgan Elizabeth; Santi, Paul M. (Paul Michael), 1964-; Maxwell, Reed M. (Colorado School of Mines. Arthur Lakes Library, 2013)
      The Macrodispersion Experiment (MADE) Site in Columbus, MS was developed to examine the reliability and predictive power of macrodispersion transport theories, used to describe the hydrodynamic spreading of solutes at the field-scale. Prior to the initial investigation reported in 1992, it was believed that the classical advection dispersion equation (ADE) was a valid model for solute transport if the subsurface hydraulic conductivity (K) was sufficiently characterized. However, the injected plume at the MADE Site displayed anomalous behavior and the classical ADE was unable to capture the early arrival time and the heavy tailing seen in the heterogeneous aquifer. At highly heterogeneous sites tracer often returns quickly after extraction begins. This quick arrival of tracer creates an early peak, likely a result of channelized preferential flow paths. Heterogeneous sites also display late-time heavy tails, which seemingly represent low K zones or dead-end pores where dissolved solute becomes relatively immobile. The resultant asymmetric breakthrough curves (BTC) led some investigators to show that non-local models may be more appropriate for modelling transport within the MADE aquifer. A temporal non-local model, the time fractional advection dispersion equation (t-FADE) may be more suitable for highly heterogeneous media because it is capable of matching the power-law tails exhibited in the MADE BTCs. This work aims to examine the accuracy of the ADE and t-FADE for the singlewell injection-withdrawal (SWIW) test conducted by Liu et al. (2010). The SWIW test was completed in the Intensively Cored Area (ICA), and used the conservative tracer NaBr. Within this area there were 4,962 recorded K values, with samples retrieved every 1.5 cm from 9 cores. This study is unique in that two components will be investigated: (1) the inclusion of the vadose zone which is often neglected in unconfined aquifers, and (2) examination of various subsurface configurations from a homogeneous domain to a detailed K-field. The inclusion of the vadose zone may account for the lowering of the water table during the extraction phase, seen in other modelling efforts (Liu et al., 2010 and Ronayne et al., 2010), and tracer being trapped in previously unsaturated areas. Also, the effects of refining the K detail will be examined, i.e., what improvements does each simulation gain by increasing the fineness of the K.
    • On the interplay between scaling small-scale reactions, mixing, and aquifer heterogeneity: human health risk implications

      Maxwell, Reed M.; Siirila, Erica R. (Colorado School of Mines. Arthur Lakes Library, 2013)
      Given the rising number of groundwater contamination scenarios involving reactive solutes, understanding fundamental interactions between aquifer heterogeneity and solute transport is crucial in assessing human health risk. Aquifer heterogeneity is known to affect solute characteristics such as spatial spreading, mixing, and residence time, all of which may influence solute concentrations. Dispersion resulting from different scales of heterogeneity is examined, ranging from the local scale (sub-grid dispersion as small as a millimeter) to the regional scale (macrodispersion due to advection as large as tens of kilometers). Finely discretized, large extent aquifers are simulated stochastically to test for parameter sensitivity and to quantify uncertainty. Stochastic numerical simulations allow the flexibility to perform controlled experiments across a range of spatial and temporal scales, and are especially advantageous when applied to probabilistic risk assessment where statistically analyzing environmental conditions can be used to inform risk management decisions. For example, by varying the spatial persistence patterns of aquifer material, feedbacks between the degree of statistical anisotropy (i.e. aquifer stratification) and plume migration are observed and quantified. I demonstrate that both the degree of statistical anisotropy and the model of heterogeneity have significant impacts not only on uncertainty quantification of solute travel time and concentration parameters, but also uncertainty quantification of human health risk. Results show that the impact of local and small-scale reactions (such a kinetic sorption) up-scale and affect far field plume behavior, where the impact is largely a function of larger, maco-scale heterogeneities. The development of a framework for time dependent risk assessment (TDRA) is also presented, and highlights how hydro-geologic processes can be used to inform a risk assessment. In contrast to traditional, time independent assessments of risk, this new formulation relays information on when the risk occurs, how long the duration of risk is, and how risk changes with time. These results are especially pertinent for forecasting risk in time, and for risk assessors and managers who are assessing the uncertainty of risk. Finally, the communication difficulties in conveying technical information in post-normal science are discussed using the example of hydraulic fracturing, or fracking. The use of documentaries in opposing information campaigns is used as an illustration. In this example we show that these techniques, and specifically the focus on a "data battle" prevent a constructive dialogue between not only the opposing information campaigns within a debate, but also between the public and scientists or technical experts.
    • Geology of the Enterprise hydrothermal nickel deposit, eastern Kabompo Dome, North-Western Province, Zambia

      Hitzman, Murray Walter; Capistrant, Patricia L.; Kelly, Nigel; Kuiper, Yvette (Colorado School of Mines. Arthur Lakes Library, 2013)
      The Enterprise nickel deposit (41 Mt at 1.07% Ni) is located within the western Domes region in the North-Western Province of Zambia. The deposit represents an apparently new style of hydrothermal nickel mineralization. The deposit area contains basement schists overlain by metasedimentary rocks of the Lower Roan Subgroup of the Katangan Supergroup. Nickel sulfide mineralization is hosted in a sequence of quartz-, carbonate-, and carbonaceous-rich metasedimentary rocks deposited within a northeast-trending graben that interfinger with and overlie the Lower Roan Subgroup basal siliciclastic metasedimentary rocks. A low angle structural zone occupied by polylithic breccia that is interpreted to have formed by halokinesis separates these rocks from overlying siltstones and dolomitic siltstones of the overlying Mwashya Subgroup and diamictites of the Nguba Group. Mafic igneous rocks occur throughout the sequence but are most abundant within and adjacent to the sequence hosting the ore. Lufilian deformation between 590 and 500 Ma produced low angle structures along the edges of Upper Roan Subgroup and locally along the basement-Katangan contact. Lufilian age metamorphism affected the entire sequence of rocks at Enterprise but well developed schistose fabrics and kyanite-bearing assemblages are restricted to the basement and the Lower Roan Subgroup rocks. Intense silicification and magnesian metasomatism apparently occurred nearly concurrently with a regional metamorphic event and resulted in talc, chlorite, and kyanite alteration of the host rocks. Mineralization resulted in the precipitation of nickel and iron-nickel sulfide minerals in veins and as semi-massive replacements of the host rocks. Nickel sulfide minerals precipitated in two main stages: 1) a millerite-vaesite-pyrite assemblage in vuggy textured rocks that forms disseminations and semi-massive replacements, and 2) a later millerite-bravoite-molybdenite assemblage that forms semi-massive replacements and occurs in quartz-kyanite veins. A discrete zone of copper sulfides underlies the nickel sulfide zones. Sulfur isotopic studies indicate Neoproterozoic marine sulfate was the primary source of sulfur at Enterprise. Carbon and oxygen isotope values at Enterprise suggest that organic carbon was not highly oxidized during the mineralization event though mineralized zones occur adjacent to highly carbonaceous sediments with total organic contents up to 17%. Re-Os geochronology yielded a 540.6 [plus-minus sign] 1.8 Ma age for mineralization at Enterprise.
    • Mineralogical and geochemical fingerprints of alteration associated with the Cripple Creek alkaline-magmatic Au-Te deposit, Colorado

      Kelly, Nigel; Rahfeld, Anne; Monecke, Thomas; Kelley, Karen (Colorado School of Mines. Arthur Lakes Library, 2013)
      The Cripple Creek alkaline-magmatic Au-Te deposit, located in southern Colorado, USA, represents a world-class gold deposit. The deposit formed within an alkaline volcanic complex dominated by a central diatreme that records a complex history of brecciation, alteration and mineralizing events. The origin of gold and tellurium in the diatreme remains enigmatic. Questions also remain about why near-mine satellite intrusions of similar magmatic affinities and inferred age are weakly mineralized or barren. The broad aim of this study was to investigate controls on mineralization by characterizing the type, intensity and timing of alteration events in the satellite intrusions and comparing the results to alteration within gold-bearing mineralized samples from within the Cripple Creek diatreme. A complex history of overprinting mineral growth and alteration could be deciphered that is interpreted to have formed as a result of an evolution of fluid composition and temperature during at least two separate fluid influx events. Alteration of trachyte in the district is described in terms of intensity of potassic alteration that controls the preservation of pre-potassic alteration events and is texturally destructive when developed intensely. Partial replacement of igneous sanidine by albite and growth of secondary amphibole is preserved in weakly altered trachyte and is part of an early sodic alteration event. With increasing intensity of potassic alteration primary igneous textures and albite are completely erased due to replacement by potassium feldspar. Potassium feldspar is overprinted by sericite, which occurs pervasively in the groundmass and is concentrated around vugs formed in intensely altered trachyte. Kaolinite partially replaces both sericite and potassium feldspar and is also most commonly formed around vugs and along fractures. This progression in alteration mineralogy from a potassium feldspar-dominated groundmass, to abundant formation of kaolinite after sericite, is interpreted to reflect the cooling path of a single hydrothermal fluid that was most likely of magmatic origin. It is possible that this fluid evolved from the same fluid that caused early sodic alteration. In intensely potassium-altered zones adjacent to breccia, potassium feldspar, sericite, and kaolinite are overprinted by biotite and Fe-hydroxide minerals that typically form along fractures in trachyte. Biotite and associated, most likely supergene, Fe-hydroxide minerals are interpreted to have formed from a hot, Fe-rich hydrothermal fluid, likely sourced from a different magmatic fluid than that responsible for the sodic-potassic alteration in these rocks. Weakly altered intrusive rocks, which formed the breccia of the satellite bodies, are preserved in the center of the breccia complexes. They are silica-poor, and relatively high in Fe compared with trachyte. These silica-poor rocks may have affinities similar to lamprophyre rocks that intrude the main diatreme. Textural relationships of clasts and matrix suggest the breccia formed after the potassic alteration event, but before both trachyte and silica-poor intrusive rocks were altered by a high-T, Fe-bearing hydrothermal fluid. It is possible this was related to a deeper, basic magmatic body. Au-telluride minerals were observed in biotite-Fe-hydroxide altered fractures, indicating a possible correlation to fluids formed in association with basic magmatic activity. Furthermore, based on comparisons between rocks of the satellite intrusive and the diatreme, gold mineralization was probably primarily controlled by the exposure to fluids, which was limited in the satellite bodies by poor availability of major fluid pathways.
    • Computational analysis of cellobiohydrolase Cel7b from Melanocarpus albomyces

      Maupin, C. Mark; Granum, David; Neeves, Keith B.; Sum, Amadeu K. (Colorado School of Mines. Arthur Lakes Library, 2013)
      Cellulases are a broad class of enzymes responsible for decomposing lignocellulosic biomass. These enzymes have several industrial applications, most notably in the production of 2nd generation biofuels from cellulosic feedstock. However, current degradation technologies involving cellulase cocktails are not sufficiently optimized for economical biofuel production on an industrial scale. Thus, there is significant incentive to further understand and improve the enzymatic degradation of cellulose by cellulase enzymes. In this thesis, constant pH molecular dynamics simulations (CpHMD), classical molecular dynamics (MD), docking calculations and kinetic modeling were utilized to evaluate the fundamental interactions impacting cellulose degradation by the cellobiohydrolase Cel7B from Melanocarpus albomyces (Ma). Presented in this thesis is an extensive evaluation of the ionizable residues in [alpha]-Conotoxin by both CpHMD and [superscript 1]H NMR, which serves as a validation of the computational pKa prediction procedures used in the subsequent thesis chapters. The procedures established in the study of [alpha]-Conotoxin were then utilized in the simulations of active site residues in Ma Cel7B. The pKa values of active site residues predicted by the simulations support the role of Glu217 as the catalytic acid-base and Glu212 as the catalytic nucleophile. In addition to predicting pKa values, the simulations identified significant charge correlations and hydrogen bonding networks that are critical to hydrolysis of the glycosidic bond. The results from the CpHMD simulations were then incorporated into a kinetic model, which further supports the hypothesis that hydrogen bonding and charge coupling are needed to achieve an optimal activity near the experimental active pH of Ma Cel7B. Beyond residue pKa values and their influence on the observed enzymatic rate, standard MD and CpHMD simulations were used to evaluation protein dynamics and loop flexibility. Investigation of peripheral loops enclosing the active site revealed structural fluctuations that are likely crucial to the binding and threading of the cellulose polymer substrate, as well as contributing to the pH and temperature tolerance of Ma Cel7B. It was found that the protonation of several residues on adjacent peripheral loops are responsible for the observed loop fluctuations and overall conformation in the free enzyme. Simulations with substrate bound in the active site reveal significant changes in the conformation and fluctuation patterns of several peripheral loop regions. The substrate induced response of the loop regions secures the cellulose polymer in the catalytic tunnel, creating an environment that is conducive for hydrolysis of the glycosidic bond. Similar loop fluctuations and dynamics are also observed when a free enzyme resides on a cellulose microfibril, indicating the role of the peripheral loops in guiding substrate into the catalytic tunnel. To further probe enzyme-substrate interactions on the hydrolysis of cellulose, the confirmation of the sugar ring at the catalytic site was investigated under different residue protonation environments. In general, the results indicate the highly charge coupled active site effectively modulates the formation of the catalytically active skewed-boat confirmation, and clearly identifies the protonation states of active site residues as the major contributing factor to the formation of the skewed boat configuration. The results presented in this thesis provide insights into molecular-level interactions that lead to the observed enzyme characteristics of Ma Cel7B, and indicate computational methods can be used to gain valuable insights into the protonation environment and specific residue pKa values that are crucial to the hydrolysis reaction performed by family 7 cellulase enzymes.
    • Geology of the Fishtie copper deposit, Central Province, Zambia

      Hitzman, Murray Walter; Hendrickson, Michael Dean; Wendlandt, Richard F.; Humphrey, John D. (Colorado School of Mines. Arthur Lakes Library, 2013)
      The Fishtie copper deposit is located in Central Province, Zambia, approximately three miles south of the border with the Democratic Republic of Congo. It contains approximately 55 Mt of 1.04% Cu at a 0.5% Cu cut-off in oxide, sulfide, and mixed oxide-sulfide ore. The deposit is hosted in the Grand Conglomérat unit and overlying Kakontwe Limestone unit of the lower Nguba Group. The Grand Conglomérat directly overlies basement schists and quartzites at Fishtie. Mineralized zones are located adjacent to high angle normal faults. The thickest successions of the Grand Conglomérat occur adjacent to these faults indicating they had synsedimentary movement. Fishtie contains iron formation within the Grand Conglomérat unit that consists of bands of nearly monomineralic to intermixed magnetite, ankerite, apatite, and quartz. Iron formation thickens towards normal faults suggesting the faults formed conduits for iron-rich hydrothermal solutions. The absence of iron formation clasts in the diamictite and presence of disseminated magnetite, ankerite, and apatite in adjacent diamictites suggests the iron formation formed by replacement of host rocks. Later hydrothermal alteration and mineralization at Fishtie overprinted the iron formation and affected the entire preserved sequence of Katangan sedimentary rocks and locally basement rocks. Copper mineralization at Fishtie is similar to that observed in some deposits of the Zambian Copperbelt where it has been attributed to interaction of an oxidized ore fluid with trapped natural gas. Copper precipitation was associated with both muscovite and chlorite mineralization, together with weak silicification. Copper sulfides at Fishtie display a relatively homogeneous distribution of generally heavy sulfur isotopic values that could have resulted from sulfide derivation from either a sour gas reservoir or thermochemical reduction of Neoproterozoic seawater sulfate.
    • In-situ photoluminescence study of the effect of wet-chemical etching on silicon quantum dots, An

      Collins, Reuben T.; Otnes, Gaute; Gorman, Brian P.; Stradins, Paul (Colorado School of Mines. Arthur Lakes Library, 2013)
      Silicon quantum dots (QDs) are interesting for many applications due to their size-tunable optical properties, combined with material abundance, nontoxicity and potential compatibility with existing silicon technology. For optimal technological implementation, good size-control of these quantum dots is essential. This thesis presents an investigation into size reduction of crystalline silicon QDs by wet-chemical etching using a mixture of hydrofluoric acid and nitric acid. The effects of the etch on the photoluminescence (PL) and absorption of the material are studied in-situ, which allows following the same population of dots in real time as they change size, without any material being added or lost. The PL peak wavelength can be blue-shifted over a wide wavelength range (>250 nm), but a lower limit to this blue-shift is observed at about 550 nm.
    • Analysis and design of a smart-inverter for renewable energy interconnection to the grid

      Simões, M. Godoy; Al-Durra, Ahmed; Reznik, Aleksandr; Ammerman, Ravel F.; Vincent, Tyrone (Colorado School of Mines. Arthur Lakes Library, 2013)
      This Master thesis presents a three phase grid connected DC/AC inverter with active and reactive power (VAR) control for medium size renewable and distributed DC energy sources. The inverter, based on a voltage sourced inverter (VSI) configuration, allows the local residential energy generation to actively supply reactive power to the utility grid, at the same time, this topology allows to work this installation in stand alone (grid disconnected) mode maintaining nominal and clean voltage at nominal power. A low complexity grid synchronization method was introduced to generate direct and quadrature components of the grid voltage in a simple and computationally efficient manner in order to generate a synchronized current reference for the current loop control. The main goal of this project is to study and to implement the control system of a grid-tied with LCL filter. The objectives of the project are divided in two parts: theoretical and experimental work. In the theoretical part, harmonics, inverter topologies, filter topologies, the design and the performance of the system will be discussed. Simulations were performed on Matlab/Simulink platform and a prototype was also developed in the lab to prove the effectiveness of the designed filter, controllers and grid synchronization method. The dSPACE hardware in the loop (HIL) was used, providing a good solution for laboratory implementation.
    • Integrated seismic and geologic analysis of Waddle Creek field in southeastern Moffat County, Colorado

      Sarg, J. F. (J. Frederick); Lin, Vivian; Sonnenberg, Stephen A.; Kluth, Chuck; Chapin, Mark (Colorado School of Mines. Arthur Lakes Library, 2013)
      The Niobrara Formation is a self-sourced resource play and unlike in conventional reservoirs, key production can occur in "sweet spots" that may extend down-dip off structure. Mapping the location and orientations of high-density fracture zones is key to identifying these productive areas in tight petroleum systems. This study integrates a 3D seismic interpretation with well log analysis and forward modeling in order to determine how high density fracture and fault zones in the Niobrara relate to regional structures and paleo-tectonic controls. Seismic curvature, variance, and ant-tracking attribute maps show 5 major thrust faults, several smaller reverse faults, a few normal faults, and a number of linear features below seismic resolution. The features identified on these attribute maps suggest transpressional tectonics with an overall WSW-ENE direction of shortening from the Laramide orogeny. During compression, the rigid Colorado Plateau to the southwest reinforced the orientation of pre-existing NW-SE trending faults in the study area resulting in strain partitioning. This formed a complex transition zone between two major NW-trending thrust faults. Production distribution suggests the existence of fracture swarms associated with this transition zone with the best production occuring along linear features that align with expected orientations for conjugate fracture sets in a left lateral strike-slip fault system. Isochrons of key time intervals highlight three major tectonic periods: Precambrian extension, Pennsylvanian uplift and erosion, and Late Cretaceous to Middle Tertiary compression. These tectonic periods are separated by intervals of quiescence and widespread, horizontal deposition. Forward modeling of the study area tests the validity of the structural history interpretation and highlights areas of high strain that may have resulted in fracture formation. The strain analysis suggests that medium amounts of strain help improve production but extremely high strains result in dry holes. One possible explanation is that overly intense fracturing allows water to flow easily through the area resulting in cementation whereas too little fracturing prevents production and thus a "medium" amount of strain is necessary to allow for production but avoid cementation. This integrated approach using seismic and well log analyses may be applied to explore other trends within the Sand Wash basin and nearby regions particularly where pre-existing structures affected stress and strain distributions during the Laramide orogeny. The relationships identified in this study between current stress regimes and paleo-tectonic controls allow for better identification and prediction of "sweet spots" when pre-existing structures affect the distribution of stress and strain. In areas where good seismic and well log data are available, the same procedures conducted in this study may be applied to produce potential high-density fracture and fault zone maps that may then be analyzed to determine the most prospective locations. Even in areas where seismic and well log data may be limited, these relationships permit exploration play trends to be high-graded for further data acquisition and analyses.
    • Effect of molybdenum on niobium, titanium carbonitride precipitate evolution and grain refinement in high-temperature vacuum carburizing alloys, The

      Findley, Kip Owen; Enloe, Charles M.; Matlock, David K.; Speer, J. G.; De Moor, Emmanuel; Richards, Ryan (Colorado School of Mines. Arthur Lakes Library, 2013)
      Existing commercial carburizing alloys can be processed at higher temperatures and shorter processing times utilizing vacuum carburizing due to the suppression of intergranular oxidation. To provide resistance to undesired grain coarsening at these elevated temperatures and associated reduction in fatigue performance, microalloyed steel variants have been developed which employ fine Ti- and Nb-carbonitrides to suppress grain growth. Grain coarsening resistance is believed to be limited by the coarsening resistance of the precipitates themselves at high temperature, so further alloy/processing developments to enhance microalloy precipitate coarsening resistance based on a greater mechanistic understanding of solute interaction with microalloy precipitates would be beneficial. Molybdenum is known to affect microalloy precipitate evolution during processing in ferrite and austenite, but a unified explanation of the role of Mo in precipitate evolution is still lacking. Accordingly, the effect of molybdenum on microalloy precipitate size and composition evolutions and the associated onset of abnormal grain growth in austenite was investigated in Mo-bearing and Mo-free, Nb,Ti-microalloyed SAE 4120 steels. Molybdenum additions of 0.30 wt pct to alloys containing Nb additions of 0.05 and 0.10 wt pct Nb delayed the onset of abnormal grain growth in hot-rolled alloys reheated and soaked at 1050 °C and 1100 °C. The coarsening rate of microalloy precipitates was also reduced in Mo-bearing alloys relative to Mo-free alloys during isothermal soaking at 1050 °C, 1100 °C, and 1150 °C. The observed microalloy precipitate coarsening rates exceeded those predicted by the Lifshitz-Slyozov-Wagner relation for volume-diffusion-controlled coarsening, which is attributed to an initial bimodal precipitate size distribution prior to reheating to elevated temperature. Heat-treatments of hot-rolled alloys (tempering and solutionizing) prior to reheating to elevated temperature in austenite beneficially affected precipitate size distribution prior to reheating, lowered precipitate coarsening rates, and delayed the associated onset of abnormal grain growth during soaking at elevated temperature. Thermo-kinetic simulations support experimentally observed effects of prior precipitate distributions on precipitate coarsening. Investigations of microalloy precipitate composition evolution indicated that Mo is incorporated into fine microalloy precipitates (<40 nm) following hot-rolling and cooling to room temperature. The molybdenum concentration gradients observed in fine precipitates in hot-rolled alloys are attributed to the precipitation sequence of microalloy carbonitrides prior to reheating. The molybdenum concentration in microalloy precipitates also varies as a function of precipitate size and total Nb addition in hot-rolled alloys reheated to 900 °C. Further reheating to 1100 °C and soaking results in a reduction of Mo concentration in microalloy precipitates due to Mo partitioning to austenite. Thermodynamic calculations support observations of reduced Mo incorporation in microalloy precipitates in austenite relative to ferrite. Possible mechanisms for the effect of Mo on Nb-rich precipitate coarsening and associated grain growth were investigated. No measurable segregation of Mo to the carbonitride-matrix interface was observed, and solute Mo is shown to have a negligible effect on Nb diffusion activation energy. It is hypothesized that Mo reduces the coarsening of microalloy carbonitrides either through a reduction in the diffusion frequency factor, particle matrix surface energy, or a combination of these mechanisms enhanced by Mo partitioning during soaking in austenite.
    • Sensitivity of fractured horizontal well productivity to reservoir properties in shale-gas plays

      Ozkan, E.; Carratu, Juan Carlos; Miskimins, Jennifer L.; Kazemi, Hossein (Colorado School of Mines. Arthur Lakes Library, 2013)
    • Investigation of microbial diversity in crude oil and seawater injection systems and microbiologically influenced corrosion (MIC) of linepipe steels under different exposure conditions, An

      Mishra, Brajendra; Olson, D. L. (David LeRoy); AlAbbas, Faisal Mohammed; Liu, Stephen; Spear, John R.; Madeni, Juan Carlos; Kakpovbia, Anthony (Colorado School of Mines. Arthur Lakes Library, 2013)
      During oil and gas operations, pipeline networks are subjected to different corrosion deterioration mechanisms that result from the interaction between the fluid process and the linepipe steel. Among these mechanisms is microbiologically influenced corrosion (MIC) that results from accelerated deterioration caused by different indigenous microorganisms that naturally reside in the hydrocarbon and associated seawater injection systems. The focus of this research is to obtain comprehensive understanding of MIC. This work has explored the most essential elements (identifications, implications and mitigations) required to fully understand MIC. Advanced molecular-based techniques, including sequencing of 16S rRNA genes via 454 pyrosequencing methodologies, were deployed to provide in-depth understanding of the microbial diversity associated with crude oil and seawater injection systems and their relevant impact on MIC. Key microbes including sulfate reducing bacteria (SRB) and iron reducing bacteria (IRB) were cultivated from sour oil well field samples. The microbes' phylotypes were identified in the laboratory to gain more thorough understanding of how they impact microbial corrosion. Electrochemical and advanced surface analytical techniques were used for corrosion evaluations of linepipe carbon steels (API 5L X52 and X80) under different exposure conditions. On the identification front, 454 pyrosequencing of both 16S rRNA genes indicated that the microbial communities in the corrosion products obtained from the sour oil pipeline, sweet crude pipeline and seawater pipeline were dominated by bacteria, though archaeal sequences (predominately Methanobacteriaceae and Methanomicrobiaceae) were also identified in the sweet and sour crude oil samples, respectively. The dominant bacterial phylotypes in the sour crude sample included members of the Thermoanaerobacterales, Synergistales, and Syntrophobacterales. In the sweet crude sample, the dominant phylotypes included members of Halothiobacillaceae. In the seawater injection sample, the dominant bacterial phylotypes included members of the Rhodobacterales, Flavobacteriales and Oceanospirillales. Interestingly, common bacterial phylotypes that are related to Thermotogaceae were identified in all investigated samples. The impact of the identified microbial communities on MIC of pipeline system was presented. On the implications front, the influence of field SRB (Desulfomicrobium sp. and Clostridiales.) on the corrosion process was complex. The bacterial activities, metabolic reactions and by-products contributed to the corrosion process. Based on the observations and results, corrosion involves multiple synergistic mechanisms. The MIC vulnerability of X52 was higher than X80 due to microstructural effects. On the other hand, the field IRB consortium (Shewanella oneidensis sp. and Brevibacillus sp.) exhibited inhibitory action on the corrosion process. The maximum corrosion rate was ~4 mpy in the biotic system and ~18 mpy in the abiotic system. Corrosion mechanisms were proposed to explain the protective behavior of the IRB consortium. On the special effects front, the influence of remnant magnetic fields (3000 Gauss strength) on MIC by a SRB consortium was investigated. The results confirm substantial increases of bacteria cell attachment, biofilm mass, corrosion and pitting penetration rates under magnetized biotic compared to nonmagnetized biotic conditions. The significant enhancement of MIC under magnetized biotic conditions has been attributed to the synergetic interaction between SRB cells and associated metabolic products with magnetic fields. The effect of magnetic fields on the thermodynamics and kinetics of the bacterial cell attachment and the electrochemical process has been presented. On the mitigation front, this work presented a pioneer study on the inhibition effects of azadirachtin (Neem) extracts of SRB influenced corrosion. The results revealed that Neem extracts reduced the biocorrosion rate by approximately 50%. Neem significantly reduced the contribution of SRB in the corrosion process by minimizing the growth of cells, which subsequently suppressed the production of sulfide, density of sessile cells and development of biofilm. Moreover, the Neem extracts might provide an organic coating that protects the surface against the medium. The work provided by this research will expand the MIC knowledge within the oil and gas industry and will improve monitoring and prevention strategies and direct future research of MIC-related issues, such as microbial injection inhibitors aided with magnetic fields applications and environmentally friendly biocides.
    • Geoelectric monitoring of seepage in porous media with engineering applications to earthen dams

      Revil, André, 1970-; Ikard, Scott J.; Mooney, Michael A.; Hale, Dave, 1955-; Delborne, Jason; Oden, Charles P.; Minsley, Burke (Colorado School of Mines. Arthur Lakes Library, 2013)
      A monitoring methodology is developed for investigating seepage and internal erosion in earthen dams with time-lapse measurements of self-potential anomalies associated with conservative salt and non-conservative heat tracer migration in the subsurface. The method allows for 1) detecting seepage zones in earthen dams and determining the preferential flow paths through seepage zones in a non-invasive manner from the ground surface, 2) monitoring the transient evolution of seepage path geometry, flow velocity, and permeability in real-time if high frequency measurements can be made, and 3) long-term non-invasive monitoring with wired or wireless sensors The method is first theoretically developed and tested in a laboratory using a conservative tracer, and then demonstrated at a 12 m high, 100 m long leaking earthen dam with complex, unknown seepage paths. The method is shown to be capable of rapidly detecting seepage zones discovered during a reconnaissance survey, and delineates the predominant seepage directions through the dam from the time-lapse self-potential anomalies. The time-lapse monitoring approach ensures improved spatial resolution, increased measurement frequencies, and improved data analysis capabilities relative to traditional approaches to seepage detection, and a cost-reduction for the application of this methodology is anticipated to follow advancements in wireless sensing and monitoring technologies. This method is designed to be a more cost-effective means of interrogating earthen dams and levees to answer questions such as: Is the dam safe? What are the geometries of the seepage zones inside of the dam, and over what spatial scale does anomalous seepage occur? What are preferential paths through the seepage zones? Is internal erosion actively occurring? At what rates are the geometries, permeabilities and flow rates of preferential seepage paths evolving?
    • Seismic interferometry for temporal monitoring

      Snieder, Roel, 1958-; Nakata, Norimitsu; Sava, Paul C.; Mooney, Michael A.; Wald, David J. (David Jay); Nakagawa, Masami (Colorado School of Mines. Arthur Lakes Library, 2013)
      Seismic interferometry, where one computes coherency of waves between two or more receivers and averages over many sources, is a technique of signal processing to reconstruct wavefields. This technique is used in geophysics, especially exploration geophysics and seismology. After more than a half century from the first study related to seismic interferometry (although the name of seismic interferometry has been used for approximately the last 15 years), researchers have developed this technique for many aspects: using multiples for increasing illuminations, enhancement of survey areas, ambient-noise analysis, and removal of the imprint of a complicated overburden. In this dissertation, I focus on the advantages of seismic interferometry for time-lapse measurements. Measurements of temporal changes yield beneficial information of fluid flow, crustal deformation, temperature, and/or stress. Estimation of temporal changes using active sources is, however, technically and economically challenging. Because seismic interferometry reconstruct waves that would have been recorded with a repeatable active sources using only receivers, this technique is appropriate for temporal monitoring. With seismic interferometry, one obtains some advantages that include canceling the complexity of wave propagation to a virtual source, creating virtual shear-wave (S-wave) sources (active S sources are expensive), and using waves that are not usable for active sources (e.g., ambient noise and multiples). I seek applications of seismic interferometry in a variety of topics (i.e., seismology, structural engineering, and exploration geophysics), and develop and/or modify several techniques of seismic interferometry for each application. Some chapters focus on developing techniques of seismic interferometry, and other chapters aim to estimate and interpret temporal changes with the developed techniques. For passive seismic sources, deconvolution-based seismic interferometry has better repeatability than crosscorrelation-based interferometry. Also, I can estimate attenuation of media with deconvolution interferometry using the amplitude decay of deconvolved waveforms. In higher-dimensional elastic cases, deconvolution interferometry allows me to obtain PP, PS, SP, and SS reflected waves without any unwanted crosstalk of P and S waves. Higher-dimensional data are more challenging for seismic interferometry, and I employ techniques such as wavefield decomposition, multi-dimensional analysis, time windowing, and time reversal to improve deconvolved waveforms obtained from earthquakes. The main discoveries in the seismological applications in addition to the techniques are that I successfully estimate near-surface S-wave velocities and azimuthal anisotropy all over Japan with deconvolution interferometry using earthquake data, that the velocities in the near surface decrease when large earthquakes occur, and that S-wave velocities at the soft-rock sites negatively correlate with precipitation. Using interferometry, I find that the 2011 MW 9.0 Tohoku-Oki earthquake significantly changed near-surface S-wave velocities and S-wave splitting in Japan. In the applications of structural engineering, the velocities of traveling waves in a building estimated from earthquakes vary grater than those in the near surface because the response of the building often includes nonlinearity caused by the shaking of the building itself. I can estimate linear responses of the building with ambient-noise data, and nonlinear and linear mixed responses from earthquake data.
    • Analysis and correlation of growth strata of the Cretaceous to Paleocene Lower Dawson Formation: insight into the tectono-stratigraphic evolution of the Colorado Front Range

      Aschoff, Jennifer L.; Harvey, Korey Tae; Trudgill, Bruce, 1964-; Kluth, Chuck (Colorado School of Mines. Arthur Lakes Library, 2013)
      Despite numerous studies of Laramide-style (i.e., basement-cored) structures, their 4-dimensional structural evolution and relationship to adjacent sedimentary basins are not well understood. Analysis and correlation of growth strata along the eastern Colorado Front Range (CFR) help decipher the along-strike linkage of thrust structures and their affect on sediment dispersal. Growth strata, and the syntectonic unconformities within them, record the relative roles of uplift and deposition through time; when mapped along-strike, they provide insight into the location and geometry of structures through time. This paper presents an integrated structural- stratigraphic analysis and correlation of three growth-strata assemblages within the fluvial and fluvial megafan deposits of the lowermost Cretaceous to Paleocene Dawson Formation on the eastern CFR between Colorado Springs, CO and Sedalia, CO. Structural attitudes from 12 stratigraphic profiles at the three locales record dip discordances that highlight syntectonic unconformities within the growth strata packages. Eight traditional-type syntectonic unconformities were correlated along-strike of the eastern CFR distinguish six phases of uplift in the central portion of the CFR.is area. The correlation of the syntectonic unconformities shows diachronous development of emerging structures that formed the CFR. The structures first developed in the South, then propagated in a northward direction along the eastern side of the CFR. Lithofacies and paleocurrent analysis within the growth strata record the transition from fluvial (confined) deposition to unconfined fluvial/megafan deposition. Sediment entry points for the fluvial (confined) and unconfined fluvial/megafan depositional systems were controlled by the lateral linking of along strike thrust faults (i.e., transverse or transfer zones) that bound the CFR. Provenance analysis supports the linkage of thrust structures controlling the provenance and sediment entry points to the Denver Basin. Petrographic analysis of twelve thin sections within the lower Dawson Formation shows two distinct petrofacies indicative of two fluvial megafan systems when considered with lithofacies and paleocurrent analysis. An unroofing signal was also identified that developed in response to the removal of Phanerozoic cover and Precambrian basement that covered the CFR due to emerging Laramide structures. The study has implication for predicting clastic sediment distribution in punctuated foreland basins, which ultimately controls reservoir presence for conventional plays and clay content for unconventional shale plays.
    • Processing, inversion, and interpretation of 9C-3D seismic data for characterizing the Morrow A sandstone, Postle field, Oklahoma

      Davis, Thomas L. (Thomas Leonard), 1947-; Singh, Paritosh; TSvankin, I. D.; Batzle, Michael L.; Benson, Robert D.; Nummedal, Dag; Sonnenberg, Stephen A.; DeVault, Bryan (Colorado School of Mines. Arthur Lakes Library, 2013)
      Detection of Morrow A sandstones is a major problem in the exploration of new fields and the characterization of existing fields because they are very thin and laterally discontinuous. The present research shows the advantages of S-wave data in detecting and characterizing the Morrow A sandstone. Full-waveform modeling is done to understand the sandstone signature in P-, PS- and S-wave gathers. The sandstone shows a distinct high-amplitude event in pure S-wave reflections as compared to the weaker P- and PS-wave events. Modeling also helps in understanding the effect of changing sandstone thickness, interbed multiples (generated by shallow high-velocity anhydrite layers) and sidelobe interference effect (due to Morrow shale) at the Morrow A level. Multicomponent data need proper care while processing, especially the S-wave data which are aected by the near-surface complexity. Cross-spread geometry and 3D FK filtering are effective in removing the low-velocity noise trends. The S-wave data obtained after stripping the S-wave splitting in the overburden show improvement for imaging and reservoir property determination. Individual P- and S-wave attributes as well as their combinations have been analyzed to predict the A sandstone thickness. A multi-attribute map and collocated cokriging procedure is used to derive the seismic-guided isopach of the A sandstone. Postle Field is undergoing CO2 flooding and it is important to understand the characteristics of the reservoir for successful flood management. Density can play an important role in finding and monitoring high-quality reservoirs, and to predict reservoir porosity. prestack P- and S-wave AVO inversion and joint P- and S-wave inversion provide density estimates along with the P- and S-impedance for better characterization of the Morrow A sandstone. The research provides a detailed multicomponent processing, inversion and interpretation work flow for reservoir characterization, which can be used for exploration in other parts of the world as well.
    • Influence of inter- and intramolecular hydrogen-bonding interactions of azo dyes on the dynamics of photo-induced anisotropy, The

      Furtak, Thomas E. (Thomas Elton), 1949-; Lo, Yu-An; Ohno, Timothy R.; Collins, Reuben T.; Knauss, Daniel M.; Marr, David W. M. (Colorado School of Mines. Arthur Lakes Library, 2013)
      In a previous study the orientation dynamics of an o-derivitized methyl red monolayer (o-dMR ML) was found to exhibit unusual sub-diffusive behavior caused by molecular interactions. From our prior study of the cis to trans thermal relaxation rate of o-dMR in solution-based experiments, we discovered an unexpected behavior that appeared to be associated with the hydrogen bonding properties of the solvents. The objective was to further investigate the influence of hydrogen bonding on cis to trans thermal relaxation and to possibly connect it to the orientational dynamic of the monolayer. The o-methylated_dMR, which has the hydrogen on the amide group of o-dMR methylated, was synthesized. The influence of the hydrogen bonding on o-dMR and o-methylated_dMR was studied through solution experiment: UV-Vis absorption spectroscopy, the measurement of the cis-trans thermal relaxation rate, and the quantum mechanical modeling. The surface characterization of the conformity, thickness and the volume density for o-dMR and o-methylated_dMR ML were done through atomic force microscopy and angle-resolved x-ray photoelectron spectroscopy. The effect of intermolecular interactions within the MLs was studied through the UV-Vis absorption spectroscopy, the measurement of the cis-trans thermal relaxation rate and the measurement of the birefringence of the MLs. The solution study indicated that the competition between intermolecular and intramolecular hydrogen bond leads to the decrease of the cis-trans thermal relaxation rate. By contrast, the intermolecular hydrogen bonding between the electron-withdrawing group of o-dMR and the hydrogen-bond donor solvent molecules increases the cis-trans thermal relaxation rate of o-dMR. The monolayer study of UV-Vis absorption spectroscopy and thermal relaxation measurement indicates that the transition and excited state of the molecules are affected by intermolecular hydrogen interactions and [pi]-[pi] stacking interactions. However, the result of the birefringence study implied that the unusual sub-diffusion kinetics of the o-dMR ML is mainly caused by the [pi]-[pi] stacking interactions rather than the hydrogen bonding interactions. The o-dMR ML develops a better photo-induced anisotropic layer than the o-methylated_dMR ML, which is mainly contributed by a faster thermal relaxation rate and a higher volume density of the o-dMR ML.
    • Method development and application for measuring representative & potential denitrification rates during wastewater reclamation in soil treatment units

      Siegrist, Robert L.; Farrell, Simon; Lowe, Kathryn; Spear, John R. (Colorado School of Mines. Arthur Lakes Library, 2013)
      Onsite wastewater systems can be designed and managed for robust wastewater treatment, reclamation and potential reuse. A typical onsite wastewater system treats wastewater utilizing a septic tank connected to a soil treatment unit. Although soil treatment units provide significant removal of many contaminants such as suspended solids, pathogens and organic content; mass loading of nitrogen remains a top concern. Previous research focused on quantifying and modeling nitrogen fate in and below soil treatment units has identified the large variability in denitrification rates as a major obstacle. A method for quantifying representative and potential rates of denitrification in soil subject to wastewater application was developed and implemented. Four columns were packed with soil classified as Seffner fine sand obtained from Central Florida. The soil had sand-silt-clay percentages of 95-1-4, respectively (% weight). This fine sand had an effective size (D10) of 0.12 mm, a uniformity coefficient of 2.3, a pH of 5 and a fraction of organic carbon ranging from 0 - 0.05 (% weight). All four soil columns were dosed two times per day at a hydraulic loading rate of 2 cm/d. Half of the columns were dosed with septic tank effluent and the other half were dosed with nitrified intermittent sand filter effluent. Effluent applied to the columns and percolate exiting the columns was characterized to facilitate a nitrogen mass balance. After 68 days of operation, two of the soil columns were deconstructed and subject to numerous denitrification rate measurements using both static core acetylene inhibition (representative rate based on actual conditions) and denitrification enzyme activity (potential rate based on optimal conditions) methodologies. Prior to application of wastewater effluent the native Seffner fine sand was subject to numerous potential denitrification rate measurements; potential denitrification rates were not detectable. After ten weeks of operation, results from the mass balance and the denitrification rate measurements indicated that the Florida soil had a low capacity for nitrogen removal. The average potential denitrification rate for the soil column receiving septic tank effluent was 0.037 mg N L-1 d-1 and the average representative rate was 0.0020 mg N L-1 d-1. The average potential denitrification rate for the soil column receiving nitrified effluent was 0.026 mg N L-1 d-1 and the average representative rate was below reporting levels. After ten-weeks of effluent application the Seffner fine sand demonstrated a statistically insignificant nitrogen removal of 0 - 16%. This removal range was accurately predicted using the nitrogen fate model STUMOD. The limited decrease in nitrogen documented by the mass balance corresponds with the low measured values for representative and potential denitrification rates. The Seffner fine sand showed an increase in potential denitrification rates after dosing with either type of effluent quality. Future research may elucidate how denitrification rates change during longer operational time periods and ultimately, techniques for optimizing denitrification in soil treatment units.
    • Pressure transient analysis of fractured wells in shale reservoirs

      Wu, Yu-Shu; Wang, Cong; Yin, Xiaolong; Tutuncu, Azra; Ozkan, E. (Colorado School of Mines. Arthur Lakes Library, 2013)
      In this study, an unconventional reservoir simulator is developed, which is based on a general black-oil simulator "MSFLOW". We incorporate several non-linear flow mechanisms (Klinkenberg effects, non-Darcy flow, gas adsorption and geomechanics effect) into the simulator. We also present a hybrid-fracture conceptual model to describe different types and scales of fractures from explicit hydraulic fractures and fracture network in simulated reservoir volume (SRV) to distributed natural fractures, microfractures, and tight sand matrix. Numerical formulation and its implementation of the simulator are validated using analytical results. Then this simulator is used to study gas flow in shale reservoirs. Three application examples are presented with this unconventional reservoir gas simulator. 1) We evaluate each of the above-mentioned non-linear flow mechanisms in a horizontal well, multi-stage hydraulic fractures reservoir scenario to see their influence on production. 2) We conduct a study of the "hydraulic fracture-matrix" linear flow and propose a methodology to estimate the total hydraulic fracture and matrix contact area. 3) We complete a history match of field data. These examples demonstrate the applicability of the reservoir simulator to modeling unconventional gas reservoirs.