Recent Submissions

  • Mass transport within the fracture-matrix systems of unconventional shale reservoirs: application to primary production and EOR in Eagle Ford

    Kazemi, Hossein; Eker, Ilkay; Tutuncu, Azra; Sonnenberg, Stephen A.; Abass, Hazim H.; Pankavich, Stephen (Colorado School of Mines. Arthur Lakes Library, 2018)
    The average primary oil recovery factor of Eagle Ford shale is around six percent; thus, a considerable amount of oil will be left behind after primary production. A major technique to enhance oil production in Eagle Ford could be gas injection because waterflooding does not seem plausible. This thesis evaluates the potential of gas injection enhanced oil recovery (EOR) using dual-porosity compositional modeling. The modeling effort focuses on three areas: transport mechanism at the matrix fracture interface, rock deformation effect on the phase behavior in the matrix pores, and multi-phase rate transient analysis (RTA). The complex nature of the fluid system and its transport in unconventional shale reservoirs requires robust computation codes that clearly reflect the physics of mass transport and thermodynamic phase behavior calculations. In this thesis, I have addressed this issue and have developed a new implicit method which relies on partial molar volume to decouple the transport equations into a pressure-composition solution, followed by a straight forward flash calculation that provides unambiguous crossing of phase boundaries, quantification of phase saturations, and phase compositions. Specifically, this formulation maintains a strong connection to the underlying physics. The pressure-composition code is an implicit numerical solution technique and is formulated for the dual-porosity reservoirs and for application in stimulated shale reservoirs. The model also includes diffusion mass transport for studying diffusion of components across the fracture-matrix interface in conjunction of with wet-gas EOR in shale reservoirs. The conclusion is that diffusion mass transport across fracture-matrix interface is a major gas-EOR mechanism even when advective flow via Darcy velocity is inactive (i.e., zero pressure gradient) or is at a very low level (i.e., very low permeability and low-pressure gradient). The new model includes a geomechanical component to study the effect of the pore pressure change and associated rock deformation on shale reservoir performance, and a pore-confinement, thermodynamic component to account for the shift in the phase envelop in nano-scale shale reservoir pores. Here, the model results indicate that fracture pore deformation during production provides additional driving force for hydrocarbon recovery. Finally, the new model was used to evaluate the rate transient analysis (RTA) in shale reservoirs where is reservoir production characteristics is highly composition-dependent. The results indicate that RTA is also applicable in stimulated shale reservoirs (i.e., dual-porosity) and RTA results provides an accurate value for the effective stimulated reservoir rock.
  • Determining osmotic pressure in Niobrara chalk and Codell sandstone using high-speed centrifuge

    Kazemi, Hossein; Uzun, Ilker Ozan; Ozkan, E.; Tutuncu, Azra; Sonnenberg, Stephen A. (Colorado School of Mines. Arthur Lakes Library, 2018)
    Low salinity waterflooding is an emerging enhanced oil recovery (EOR) technique that has attracted the attention of the oil industry. However, the classical application of waterflooding in unconventional shale reservoirs is impractical because of the nanoscale dimension of the matrix pores. Salinity contrast across shale matrix blocks leads to osmotic pressures which expels oil from tight shale. This thesis exploited this phenomenon to measure osmotic pressure in shale core plugs. Typically, all the unconventional shale reservoirs produce hydrocarbon after hydraulic fracture stimulation. The stimulation treatment is performed using slick water and some gel components. A large percentage of this injected fluid is trapped inside the pores and cannot be produced. The findings and results of this thesis can be used to investigate the osmotic effect of the hydraulic fracturing fluids in tight shale formations. This thesis includes measurement of osmotic pressure using ultra-high-speed centrifuge experiments and calculation of membrane efficiency for unconventional Niobrara chalk and Codell sandstone formations. The laboratory experiments show that the low-salinity brine is imbibed into the core samples in greater quantities compared to that of high-salinity brine. The brine imbibition is measured by displacement and production of resident oil in the core. Measured membrane efficiency of Niobrara B-Chalk, with permeability of 0.0022-0.0099 md, is 75 % of perfect membrane. Accounting for chalk solubility in brine within the pores should reduce the membrane efficiency to about 50%. Similarly, measured membrane efficiency of Codell sandstone, with permeability of 0.0085-0.0105 md, is 2.4 % of the perfect membrane.
  • Grand Canonical Monte Carlo simulation model for phase behavior of confined hydrocarbons, A

    Ozkan, E.; Coskuner, Yakup Berk; Kazemi, Hossein; Yin, Xiaolong; Miskimins, Jennifer L.; Sonnenberg, Stephen A. (Colorado School of Mines. Arthur Lakes Library, 2018)
    With the increased interest in primary and improved recovery from unconventional reservoirs, unusual characteristics of PVT behavior in nano-pores have attracted more attention. It has been established that the pore size influences thermodynamic properties and PVT behavior of the reservoir fluids due to the change in inter-molecular, capillary, and surface forces. There have been a number of studies on phase behavior in nano-pore confinement which reveal inconsistent and contradicting results about the shift of the critical point and the shift of the pressure-temperature diagram. This thesis focuses on Monte Carlo simulation technique taking the statistical mechanics into account to model the PVT behavior of hydrocarbons. Grand Canonical Monte-Carlo ensemble is studied to observe the effect of confinement on phase behavior of pure methane by taking into consideration the effects of the inter-molecular forces and the interaction between fluid particles and solid surface. Under isothermal conditions, density of methane is calculated from Monte Carlo simulation at different pressures to determine the bubble point. Results are compared with the published studies and the differences are discussed. The size of the simulation box affects the results of Grand Canonical Monte Carlo simulation significantly. Therefore, this thesis questions some of the conclusions drawn in the literature about the bubble point and the critical point shift. Consequently, it is suggested that the results of molecular simulations should not be used as absolute phase-behavior benchmarks in nano-pore systems without confirmation by independent means.
  • Advanced control of converters with multitask functionalities in distribution grid systems based on conservative power theory

    Simões, M. Godoy; Mortezaei, Ali; Arkadan, Abd A.; Ciobanu, Cristian V.; Sen, Pankaj K. (Colorado School of Mines. Arthur Lakes Library, 2018)
    Distributed generation (DG) play a very important role in the modernization of electric power systems, it is estimated their increasing share of operation in the near future. In addition, there is growing concern on the environmental issues, lack of transmission capacity and limitation in constructing new lines, and increasing demand of energy, that would support a more flexible inverter control, capable of interacting users with the utility grid. The main objective of such a system is providing active power, which is the primary use to balance loads. However, power electronic systems can provide power quality improvement and DG systems would then be used as multi-functional compensators for improving power quality, instead of only balancing or selling active power to the grids. In this context, this dissertation first studies the well-known instantaneous current decomposition theories highlighting the important contributions based on the Instantaneous Power (PQ) theory and the Conservative Power Theory (CPT) and presents a comprehensive comparison from performance and computational complexity perspectives. Although these theories are quite distinct in their formulations, the central idea is to make a comparative study between the current portions and their respective portions of power, in order to show the similarities and divergences between them in terms of characterization of the physical phenomena and in terms of disturbing current compensation. The studied instantaneous current decomposition techniques are then used to provide selective functionalities in distribution systems. Therefore, it is possible to inject active power plus compensate selectively unwanted current terms (reactive, unbalance, and distortion), enabling full exploitation of the inverter capability and increasing its overall cost-benefit and efficiency. Afterwards, control structures with multitask functionality to the grid side converter of the renewables to carry out the power quality ancillary services in the distribution system are developed. The key diversity of the methodologies we proposed in this project with respect to others in the literature is that the developed control structures on the grid side converters are based on the CPT theory. This choice provides decoupled power and current references for the grid side inverter control, which offers very flexible, selective and powerful functionalities. These qualities make the system to be the benchmark for achieving 100% renewable and sustainable grid with multifunctional capabilities. This thesis then proposes the coordinated control of the aforementioned multifunctional interfacing DG systems to enhance the operation of microgrid systems. Based on our proposed method, a hybrid cooperative strategy is developed that overcomes limitations in communication-based and non-communication-based approaches for the coordinated operation of multifunctional distributed generators in islanded microgrid systems. Two important issues that are addressed are the power quality and undesirable current sharing, particularly in the low-voltage distribution network, where electronic devices are drawing distorted and unbalanced currents. The interactions of such current disturbances with high feeder/line impedances, in a low voltage system cause considerable voltage deterioration and possibly affect sensitive loads showing the requirement for power quality enhancement. Finally, this thesis explores the study and implementation of cascaded multilevel converters, in which the primary concepts relating to modulation, structure, and control schemes are detailed. These topologies are composed of series-connected H-bridge converters with isolated DC links. Therefore, it is possible to integrate renewable energy and storage resources to power grids. The experimental findings validate the applicability and performance of the proposed control strategies in distribution grid systems.
  • Hydrogen storage in porous crystalline materials: insights on the role of interaction strength from simulation and machine learning

    Gómez-Gualdrón, Diego A.; Schweitzer, Benjamin; Carreon, Moises A.; Sum, Amadeu K. (Colorado School of Mines. Arthur Lakes Library, 2018)
    Hydrogen is a promising renewable fuel due to its carbon-free nature and relatively high energy content by mass. However, a major hurdle for its widespread adoption as a vehicular fuel is its low density at ambient conditions, posing a challenge for onboard storage. Toward fully realizing a cost-effective, hydrogen-powered fuel cell vehicle, the U.S. Department of Energy (DOE) has set a system-level hydrogen storage target of 30 g/L for 2020, which is expected to require storing around 60 g/L at the material-level. While considerable research has been performed on hydrogen storage materials, it is still unclear whether these storage demands can be met by physisorption-based hydrogen storage systems. To assess the viability of these targets, grand canonical Monte Carlo (GCMC) simulations were used to calculate 18,000+ hydrogen loadings in porous crystals featuring catecholate functionalities at different thermodynamic conditions. From the data, the effects of interaction strength on the deliverable capacity of the material were elucidated. The simulation data was also used to develop an artificial neural network (ANN) model to predict hydrogen loadings using the force field parameters, textural properties of the crystal and thermodynamic conditions as input. The model was used to explore optimal operating conditions for hydrogen storage beyond those initially simulated with GCMC. It was found that optimizing the H2-catecholate interaction strength allowed some porous crystals to achieve deliverable capacities of 60 g/L with a 100 bar/77K ↔ 5 bar/160K swing in pressure and temperature. Additionally, it was shown that other porous crystals can reach 95% of the above deliverable capacity with a storage pressure of only 20 bar as long as the H2-catecholate interaction strength is optimized.
  • Density functional theory analysis of solute-defect interaction energies in fcc iron: fundamental origins and industrial application, A

    Speer, J. G.; Hoerner, Michael; Eberhart, Mark E.; Findley, Kip Owen; Van Tyne, C. J.; De Moor, Emmanuel (Colorado School of Mines. Arthur Lakes Library, 2018)
    This project was initiated to develop an understanding of the origin of solute drag on fcc Fe (austenite) grain boundaries and explain differences in the experimentally observed solute drag effects of different solutes in steels, and use this understanding to predict solutes which could be of industrial interest as grain growth inhibitors in austenite. The 3-d and 4-d (period 4 and 5) transition metal elements on the periodic table are considered as substitutional solutes with specific attention given to selected solutes (Nb, Mn, Cr, Mo, and Ni) that are of particular interest to the steel industry. Atomistic modeling using both density functional theory (DFT) and molecular dynamics (MD) are used to achieve these goals. The simulations provided thermodynamic solute-boundary binding energies as well as information about the electronic structure of the system which was accessed using both density of states analysis and direct observation of the calculated charge density. The calculated thermodynamic solute-boundary binding energies correlate strongly with experimental data sets on the effects of solutes on both austenite grain coarsening and austenite recrystallization. The strong correlation with experimental results provides confidence in the modelling work and enables the results to be used to suggest solutes of interest for possible future experimentation as alloying elements. Of particular interest, according to the results, are Y, Zr, and Sc, with possible specialized applications for Pd, Ag, and Cd. The filled kite is identified as a fundamental building block for the grain boundary structure of fcc Fe tilt grain boundaries. This structure is found to function as a chemical sub-structure within the grain boundary. This study characterizes the chemical structure of the filled kite through topological analysis of the charge density and density of states analysis. Further, the solute-defect interaction energy with this structure is relatively independent of the orientation of the filled kite with respect to the grain boundary, leading to the conclusion that understanding the interaction of defects with this structure enables a more complete understanding of the interaction of solutes with general grain boundaries. The most significant finding of this work, presented in Chapter 4, is that the solute-defect interaction energy can be predicted based upon the elemental properties of the solute-solvent system and the structure, both electronic and geometric, of the grain boundary. The chemical and strain interaction energies can be separated by considering changes in the Bader volume and Bader charge, respectively, of the solute and solvent atoms as they move from the bulk to the defect. Through this separation of the chemical and strain energies, it is determined that the chemical hardness, the second derivative of the energy with respect to the electron count, of the solute relative to the solvent is the fundamental elemental property leading to the chemical energy of segregation just as the volume of the solute relative to the solvent is the fundamental elemental property leading to the strain energy of segregation.
  • Utilization of metal-organic frameworks for gas separations and catalytic oxidation

    Trewyn, Brian; Evans, Tabitha J.; Carreon, Moises A.; Richards, Ryan; Pylypenko, Svitlana (Colorado School of Mines. Arthur Lakes Library, 2018)
    Metal-organic frameworks (MOFs) and their applications have been a rapidly growing area of research in recent years. The seemingly endless combinations of metal ions or clusters with various possible organic linkers, along with the methods of post-synthesis modification, has resulted in approximately 20,000 different MOFs to date. With such potential for variation, MOFs have shown to be useful in a whole host of applications. One such application of MOFs is the separation of natural gas. Currently, these separations require expensive methods, such as amine absorptions and cryogenic distillation. Polymers, such as polyimide, have been investigated, but the necessary high temperatures lead to plasticization and poor separation performance. Alternatively, ZIF-8 (zeolitic imidazolate framework 8), a member of the ZIF class of MOFs, is a viable option due to its inherent pore size and preferential adsorption of carbon dioxide. Microporous carbon membranes have shown increased chemical and thermal stability. By converting the microporous ZIF-8 to a carbon membrane, the resulting membrane can be expected to maintain the separation properties of the parent ZIF-8 while gaining additional stability provided by carbon. Unfortunately, synthesizing this material is a challenge to reproduce due to the wide variety of methods for ZIF-8 synthesis and the limited study of the effect of carbonization on the parent material A second application of MOFs is as heterogeneous catalysts. Cu-BTC, or HKUST-1, is used for the oxidation of benzyl alcohol to benzaldehyde, a chemical commonly used in perfumery and pharmaceuticals. However, the use of copper requires the presence of TEMPO (2,2,6,6-tetramethylpiperidine-N-oxyl) as it is needed to deprotonate the alcohol. Unfortunately, TEMPO can interrupt the framework structure of Cu-BTC and poisons the catalysts. In order to help combat this problem, layer by layer synthesis of Cu-BTC was used to incorporate the MOF into the pores of a functionalized mesoporous silica nanoparticle (MSN). However, this incorporation did not protect the Cu-BTC, as the pores size of the protective MSN was insufficient to prevent TEMPO access. Additionally, only a small amount of Cu-BTC was synthesized within the pores, which magnified the effects of TEMPO poisoning.
  • Hydraulic fracture modeling of an enhanced geothermal system (EGS) experiment

    Miskimins, Jennifer L.; Ozkan, E.; Kutun, Kagan; Yin, Xiaolong; Johnston, Henry (Colorado School of Mines. Arthur Lakes Library, 2018)
    Enhanced geothermal systems (EGS) are analogous to the unconventional reservoirs of the oil and gas industry in size and extent. EGS reservoirs lack the presence of a reservoir fluid and a naturally permeable rock. The total energy reserves that can be classified as EGS are larger and more numerous compared to conventional geothermal systems. Unfortunately, they cannot be produced by conventional means. In order to capitalize on EGS, one must artificially induce a permeable network within these mostly igneous/crystalline rocks. The fractures allow the fluid, while being circulated from an injection to a production well, to harvest and bring some of the in-situ heat to surface. Abstract The EGS Collab is a research project sponsored by the United States Department of Energy. The aim of the project is to provide a test bed at intermediate scale with the main focus on understanding and prediction permeability enhancement in crystalline rocks. The project involves the collaboration of multiple national research laboratories and universities. The experiments take place 4850 ft below the surface in Sanford Underground Research Facility (SURF) located at Lead, South Dakota. Abstract In this research, the behavior of hydraulic fractures in an EGS setting is investigated numerically, using CFRAC, a hydraulic fracture simulator, to support EGS Collab. The work encompasses the prediction of the hydraulic fractures which are created within SURF, the preliminary investigations of the experimental results, and the investigation of the model's behavior in a crystalline rock setting. Abstract The modeling process produced results that agree with initial field results. The experimental hydraulic fractures are affected by the presence of the mine drift and natural fractures. Presence of a natural fracture halted the growth of the hydraulic fracture. Furthermore, the preliminary analysis of the experimental data showed that an active natural fracture network can influence the falloff signal to a degree that the closure events are masked completely.
  • Construction and seismic testing of a resilient two-story mass timber structure with cross laminated rocking walls

    Pei, Shiling; Griesenauer, Daniel R.; Crocker, Joseph P.; Guerra, Andres (Colorado School of Mines. Arthur Lakes Library, 2018)
    With the rising popularity of mass timber building in the United States, there is a need to develop efficient wood-based lateral systems to enable design of mass timber buildings in regions with high seismicity. This thesis summarizes the construction and testing details of a full scale shake table testing program for a two-story mass-timber structure with a resilient post-tensioned rocking wall lateral system made from cross laminated timber (CLT) product. The post-tensioned rocking walls helped to dissipate seismic forces while allowing the other parts of the structure to remain damage-free through multiple seismic events. The utilization of a balloon framing style rocking wall system and heavy timber gravity frame enabled an open floor plan (compared to compartmentalized CLT construction) that has better potential for modern commercial and office use, which can help improve market competitiveness of mass timber construction. Since the work conducted in this thesis is only part of a large multi-university collaborative research project aiming at designing tall wood buildings for high seismic regions, only the construction, testing process, and resulted data related to building resiliency are discussed. The details and data that are in part presented in this thesis are to serve as a benchmark dataset for dynamic performance of this new building type that can be referenced by the wood design community. The first part of the thesis discusses design considerations, construction methods, and instrumentation setup employed in the test program. Practical issues encountered during construction and testing were also discussed together with suggestions for improvement in the future. The second part of the thesis presents the data collected from the shake table tests, with comparison to initial design assumptions. The final section of the thesis contains some conclusions that can be drawn from direct observations of the test results.
  • Quantification of timing uncertainty in a correlation based channel sounder

    Elsherbeni, Atef Z.; Kast, Joshua M.; Quimby, Jeanne; Hadi, Mohammed; Arkadan, Abd A. (Colorado School of Mines. Arthur Lakes Library, 2018)
    Untethered radio channel sounders use stable frequency standards to synchronize physically separated transmitters and receivers, allowing for practical propagation measurements in complex environments such as cities, factories, and offices. In this paper, measurements of the timing-uncertainty of an untethered, correlation-based channel sounder are presented. Timing results are characterized using both deterministic predictions of timing-drift, as well as analysis of timing-noise using the modified Allan deviation. The 1-6 GHz, correlation-based channel sounder used in this experiment uses a pair of rubidium clocks to provide synchronization between the transmitter and receiver. Measurements of up to 7 days in length were made to determine the long-term behavior of the timing system. We show that the use of rubidium clocks, common to many channel sounders, introduces both deterministic drift as well as several forms of timing noise into channel sounding measurements. This work extends upon existing literature by providing measurements of both timing drift and timing noise, using multiple system configurations, over long test durations.
  • Integrated analysis, reservoir characterization, and resource potential of the Niobrara Formation: Lowry Bombing Range, Arapahoe and Adams County, CO

    Sonnenberg, Stephen A.; Bane, Lauren T.; Anderson, Donna S.; Emme, James J.; Bordoloi, Sandip (Colorado School of Mines. Arthur Lakes Library, 2018)
    The Cretaceous Niobrara Formation is a productive, unconventional petroleum exploration target in the Denver Basin, Colorado. It is a self-sourced oil and gas play composed of alternating chalk and marl units. Ductile marls can serve as major source rocks with TOC values ranging 2-8 wt. %. These marly intervals can also serve as seals for the underlying brittle chalk reservoirs. Chalk intervals are comprised of carbonate-rich pellets, coccoliths, pelagic foraminifera, inoceramids, and oyster shells, and tend to have higher porosity and permeability values. Porosity distribution is controlled by the abundance of pellets, degree of bioturbation, and mineralogy within the chalk-marl matrix. Characterizing the pellet abundance and the depositional fabric provides a foundation for predicting the occurrence and distribution of reservoir intervals of the Niobrara Formation. This study involves a comprehensive evaluation and integrated approach for characterizing the reservoir potential in three wells from the Lowry Bombing Range in Arapahoe and Adams counties, Colorado. Goals of the project include: (1) a complete core description and identification of facies with an understanding of lateral and vertical heterogeneities; (2) reservoir characterization using petrographic thin sections, SEM photomicrographs, XRD bulk mineralogy, XRF analysis, GRI porosity/permeability data, and Source Rock Analysis; (3) a comprehensive description of the pore system and storage capacity; (4) a geomechanical evaluation of fracture-prone benches and fabrics that enhance brittleness; (5) identification of potential reservoir targets within the Niobrara Formation; and (6) an evaluation of the influence of regional paleo-high structures on thermal maturity and the total petroleum system. Ultimately, this study aims to identify the geologic parameters that contribute to productive wells throughout the Lowry Bombing Range. Nine chalk-marl facies were identified by describing the cores at high resolution for lithology, mineralogy, degree of bioturbation, sedimentary structures, fossil presence, contacts, and pellet abundance. Primary reservoir facies include pellet-rich marly chalks and bioturbated chalks to marly chalks. Carbonate-rich pellets appear to experience less compaction than the surrounding matrix and can maintain storage capacity for Niobrara rocks. Based on GRI data, average porosity and permeability values in reservoir facies were about 8% and 6.3E-4 mD, respectively. SEM photomicrographs indicate that storage capacity in pellets is dominated by intraparticle and interparticle porosity. The A, B2, and C Chalk intervals were defined as primary reservoir targets based on high carbonate concentration, low clay material, high porosity and permeability, favorable geomechanical properties, and high gas saturation. Based on subsurface correlations and mapping, the B Chalk is the thickest reservoir with the highest resistivity responses suggesting the best potential for hydrocarbon production.
  • Simulation of proppant transport in slickwater with DNS-derived drag correlations

    Yin, Xiaolong; Li, Xiaoqi; Tilton, Nils; Miskimins, Jennifer L.; Zerpa, Luis E.; Gutierrez, Marte S.; Smits, Kathleen M. (Colorado School of Mines. Arthur Lakes Library, 2018)
    This dissertation is developed to address a need of multiphase flow models for proppant transport: problem-relevant drag correlations. This dissertation consists of small-scale simulations by direct numerical simulations (DNS) and larger, fracture-scale simulations by MFIX (Multiphase Flow with Interaction eXchange). DNS was employed to study the influences of several dimensionless numbers, namely the Reynolds number of cross flow, 〖Re〗_x, the Archimedes number, Ar, consisting of gravity, density difference, slickwater viscosity, and proppant size, the density of proppants relative to that of the fracturing fluid, ρ_p⁄ρ_f , the ratio of fracture width over proppant dimension, W⁄d_p , and proppant concentration, ϕ_s. Another independent parameter was firstly evaluated in this study is the inclination angle of fracture, θ. DNS results show that W⁄d_p plays a significant role in proppant transport. Narrower fractures impede proppant settling more. Cross flow and proppant density over that of fluid (provided that Ar is held as a constant) were found to have negligible effects on the settling velocity. Ar, ϕ_s, and inclination were found to have significant influences on settling. When factures were placed with a large fracture width, the effect of proppant concentration on settling was found to be reversed from that in vertical fractures. The lower the proppant concentration, the slower proppants settle. The aim of DNS was not only to understand the influence of the dimensionless numbers, but also to obtain data for developing drag correlations. Drag correlations were developed from DNS data using quadratic polynomials and interpolations. These drag correlations were incorporated into MFIX to close the momentum equations of fluid and solid phases. MFIX simulation results include the rate of proppant bank formation and the equilibrium height and transition length of the end proppant distribution. First, DNS-derived drag correlation predicted slower proppant bank formation compared to other default drag laws, because proppant settling speed is slower in narrow fractures, a factor that to date has not been considered in proppant transport simulations. Second, the influences of key parameters, proppant size, proppant density, proppant concentration, fluid viscosity, and inclination, on proppant bank formation and distribution, were found to be mostly consistent with their roles in affecting the settling velocity. Higher settling velocity always leads to more rapid formation of proppant banks and shorter transition length. Equilibrium height of proppant bank generally increases with increasing proppant concentration and decreases with increasing fluid viscosity.
  • Solid-state joining of titanium alloy to stainless steel

    Yu, Zhenzhen; Gilbert, S. Michelle; Liu, Stephen; Findley, Kip Owen (Colorado School of Mines. Arthur Lakes Library, 2018)
    Titanium has a wide variety of applications in a multitude of industries but can be costly in large quantities. To reduce the amount of titanium alloys needed and therefore the cost of materials, some suggest designing parts made with both titanium alloys and stainless steels. Current joining methods produce intermetallic compounds (intermetallics) at the joint interface which are detrimental to joint strength. In this study, dissimilar joints between 436L stainless steel and a titanium alloy, Ti 1.2 ASN, were made by the solid-state welding methods of vaporizing foil actuator welding (VFAW) and mash seam resistance welding (MSW). A Nb interlayer was used in the MSW process as a diffusion barrier due to the relative higher heat input and longer welding time in comparison to the VFAW process. The welds were evaluated to identify correlations between microstructural and mechanical properties. Microstructural characterization of the base materials and solid-state joints was performed by optical microscopy, scanning electron microscopy (SEM) with energy dispersive x-ray spectrometry (EDS) and hardness testing using both Vickers microhardness and nanoindentation. Mechanical properties were tested by means of tensile and tensile-shear testing with in-situ digital imaging correlation (DIC) to map localized strain. In the VFAW joints, jet-trapped zones and discrete regions of Ti-Fe intermetallic compounds were observed along the weld interface. The maximum shear strength was observed to be about 227 MPa and failure occurred through the Ti 1.2 ASN base material. In the MSW joints, the 436L stainless steel reacted with the Nb interlayer and formed a hard reaction layer ranging from 42 μm to 480 μm in thickness that was rich in Cr, Fe, and Nb. No reaction between Ti 1.2 ASN alloy and the Nb interlayer was observed. The maximum tensile strength for this samples was about 428 MPa. The MSW joints did not fail at the joint interface despite the presence of a hard reaction layer, this could be partly attributed to the larger thickness in the lap-joint geometry than that of the base materials.
  • Release of bioactive agents from mesoporous silica nanoparticles for biological applications

    Trewyn, Brian; Adams, Marisa L.; Boyes, Stephen G.; Posewitz, Matthew C. (Colorado School of Mines. Arthur Lakes Library, 2018)
    The high surface area, pore volume, and biocompatible/ biodegradable silica matrix of mesoporous silica nanoparticles (MSN) has led to extensive investigation into these materials as carriers for bioactive agents. These agents can be loaded into and sheltered within the mesopores, then released at the target site either through simple diffusion or in response to specific stimuli. Owing to the facile surface modification of MSN, stimuli responsive MSN is frequently synthesized through the covalent linkage of an organic functionality, capable of changing conformation in response to a given stimuli, to the silica surface. However, this goal can also be accomplished through coating of the particle surface with an enzymatically digestible polymer. In this work, vanillin loaded MSN coated with the linear glucose polymer amylose or branched glycogen is proposed as a salivary α-amylase responsive system for drug delivery. The starch cap is capable of retaining vanillin within the MSN pores until the enzyme is introduced, making delivery specific to the oral cavity. This target offers benefits such as higher patient compliance and the negation of first-pass metabolic effects. In addition, the use of large pore MSN for the release of large, homotetrameric protein and silver-MSN nanocomposites for antimicrobial applications are discussed.
  • Spectrally resolved fluorescence microscopy and its applications for single molecule characterization

    Sarkar, Susanta K.; Czerski, John; Squier, Jeff A.; Durfee, Charles G. (Colorado School of Mines. Arthur Lakes Library, 2018)
    Spectrally resolved fluorescence microscopy is an important tool for measuring biological systems at the single molecule level. Spectral resolution provides a means for unambiguous identification and a tool for characterizing heterogeneity. Fluorescence microscopy facilitates single molecule measurement by limiting contrast to only those molecules that are capable of producing fluorescence when illuminated with the excitation source of the system. In the following thesis I describe my work combining spectral resolution with a fluorescence microscope by developing a hyperspectral prism-type total internal reflection fluorescence microscope. The microscope has a tunable supercontinuum laser excitation source along with 3 CW solid state lasers and has the ability to separate a field of view into 4 spectral channels which are imaged simultaneously. We used the microscope to characterize the photoluminescence excitation spectrum of individual fluorescent molecules and measure F\"{o}rster resonant energy transfer from inter-domain motion of matrix metalloproteiase for the first time. This versatile platform facilitates high throughput single molecule measurements in which multiple properties can be studied simultaneously.
  • Characterization of a vector network analyzer based millimeter-wave channel sounder

    Elsherbeni, Atef Z.; Weiss, Alec; Quimby, Jeanne; Hadi, Mohammed; Arkadan, Abd A. (Colorado School of Mines. Arthur Lakes Library, 2018)
    As the world moves into 5G communications systems, many cellular networks will extend their reach past sub 6GHz bands into millimeter wave (mmWave) bands. The mmWave frequencies provide a greater bandwidth to supply the higher data rate requirements for 5G networks. One step to meet the 5G network development to make this technology a reality is reliable mmWave channel models. These channel models are developed through the direct measurement of mmWave propagation channels. To provide reliable channel models at mmWave frequencies, a comprehensive characterization of the performance and uncertainty of the channel sounder hardware is very important. This thesis will critically review measurement techniques that were developed to characterize the channel sounder based around a vector network analyzer. These techniques provide a novel approach to developing a channel sounder measuring 3 dimensional synthetic aperture data with uncertainties. The end goal of this research is to provide a highly fexible channel sounding system whose errors are fully bounded to provide channel models with uncertainties at mmWave frequencies for 5G wireless systems. The Synthetic Aperture Measurements with UnceRtainty and Angle of Incidence (SAMURAI) system developed in this paper was built specically for this purpose.
  • Synthesis of poly(lactide)-based amphiphilic block copolymers and hydroxyapatite nanoparticles for bone tissue engineering applications

    Boyes, Stephen G.; Smith, Patrizia P.; Krebs, Melissa D.; Posewitz, Matthew C.; Trewyn, Brian (Colorado School of Mines. Arthur Lakes Library, 2018)
    Due to the drawbacks associated with traditionally used bone substitutes, such as autografts and allografts, the field of tissue engineering, regenerative medicine and biomaterials science has recently come to the forefront with new strategies for bone repair and de novo tissue formation. Current research has focused on employing bionanocomposites composed of polymers, such as poly(lactide) (PLA), and inorganic calcium phosphate ceramics, such as hydroxyapatite (HA). These hybrid materials benefit from combining biodegradability, biocompatibility, bioactivity, and other advantageous scaffold properties to better mimic biological and structural characteristics of native bone. With this in mind, the work presented in this dissertation focuses on the synthesis of well-controlled PLA homopolymers, as well as amphiphilic block copolymers. This was achieved via the ring opening polymerization (ROP) of lactide using an organocatalyst and the successful combination of ROP of lactide and the reversible addition-fragmentation chain transfer (RAFT) polymerization of poly(ethylene glycol) ethyl ether methacrylate (PEGEEMA) using a novel heterofunctional initiator/chain transfer agent (inifer). Comprehensive kinetics studies also provided valuable insights into the factors influencing the synthesis of well-defined block copolymers. These polymers were then successfully processed into fibrous scaffolds using electrospinning techniques and the different parameters affecting fiber formation and morphology were investigated. In addition, the prepared scaffolds were evaluated in terms of overall hydrophilicity, in vitro performance, and biodegradation behavior. Furthermore, a hydrothermal synthesis approach was employed to produce well-defined HA nanoparticles with tunable sizes that can be used in biomimetic nanocomposite scaffolds. Lastly, the surface modification of the HA nanoparticles was investigated via a grafting-from approach using the ROP of lactide, as well as via the use of a poly(dopamine) coating. Overall, the results presented in this dissertation provide important mechanistic insights into the successful synthesis of well-controlled amphiphilic block copolymers and also contribute to developing facile methods to prepare biomimetic HA nanoparticles and biodegradable fiber scaffolds. The findings also further highlight the importance of polymer and nanoparticle-containing bionanocomposite scaffolds, which have the potential to greatly improve the treatment of bone defects and bone loss.
  • Isotopic analyses of helium from wells located in the Four Corners area, southwestern US

    Sonnenberg, Stephen A.; Halford, Daniel Thomas; Carr, Mary; Cuzella, Jerome J. (Colorado School of Mines. Arthur Lakes Library, 2018)
    Helium, the lightest noble gas, is a valuable resource located on the Colorado Plateau southwestern US. Helium, a proven, useful noble gas, has many applications in modern technology for its chemical, physical, and thermodynamic properties. As of this writing, the price of crude helium is ~40% greater than CH4, rendering the economic grade for direct and secondary extraction at 0.3% helium. The helium systems in the Four Corners area (i.e., the study area) are characterized utilizing the geochemistry of noble gases, hydrocarbons, and non-hydrocarbons (compositional and isotopic), as well as geologic mapping. The geochemistry delineates sources of gases, migration pathways, and potential trapping/sealing mechanisms of the helium system, which is a slight deviation from the petroleum system. Economic helium (>0.3%) is primarily found in Paleozoic intervals structurally trapped on the Four Corners Platform, the edge of the Defiance Uplift, and the edge of the Holbrook Basin. Thirty-one gas samples, isotopically analyzed, are from actively producing Paleozoic formations within five fields: Tocito Dome, Dineh-Bi-Keyah, Ratherford, Pinta Dome, and Navajo Springs. Helium concentrations range from 0.01% to >6.0% and incorporates a spectrum of other gas values associated with relatively similar Paleozoic formations. Noble gases along with hydrocarbon and non-hydrocarbon gas geochemistry are successfully used in genetically fingerprinting gas families. The source of helium is determined to be from the shallow crust, i.e., Precambrian granitic basement. Noted faults and attendant fracture systems serve as primary migration conduits (via fluid flow from advection). Observed gas-water reactions indicate groundwater involvement in the concentration of helium and extreme solubility fractionation (i.e., long secondary migration pathways). By investigating migration pathways, N2 and CO2 are recognized as major, helium carrier gases, whereas CH4 is a helium dilutant. Geologic mapping illustrates dominant structural, stratigraphic, and combination structural-stratigraphic traps. The helium system definition is updated, as well as criteria developed to successfully explore for helium. Proper isotopic and geological analyses can improve helium system models that involve generation, migration, and trapping/sealing mechanisms. Improvements in the understanding of the helium system model are critical for more effective helium exploration. Native Americans Tribes of the Southwest and other economic sectors stand to benefit (economically and socially) from a more enhanced scientific knowledge of the helium system in the study area.
  • Numerical modeling and ray tracing of SPatIal Frequency modulation for Imaging

    Squier, Jeff A.; Skogen, Brandon J.; Durfee, Charles G.; Kohl, Patrick B. (Patrick Brian) (Colorado School of Mines. Arthur Lakes Library, 2018)
    This thesis presents the first full geometric and physical optics characterization of aberrations and the performance of a simple system that implements SPatIal Frequency modulation for Imaging (SPIFI). SPIFI utilizes a chirped frequency mask that modulates the intensity of light along a single axis at a linear frequency sweep giving each lateral position a unique spatial frequency. By taking the Fourier transformation of the voltage verses time readout of a single element detector position data can be extracted for each point along the modulation axis. The geometric analysis is performed using Fraunhofer diffraction and conjugate imaging planes in a Fourier optics based approach. The ray tracing analysis is performed using the ZEMAX software for configurations involving achromatic lenses, flat field lenses, and a specialized lens array setup. Lastly, a unique SPIFI design setup is presented making use of a reflective scanned SPIFI mask to achieve random access imaging using three distinct spots for simultaneous imaging.
  • New opportunities in the mature fields of the central Illinois Basin: a case study of the Mode field, Shelby County, IL, USA

    Wood, Lesli J.; Huels, Matthew L.; Sonnenberg, Stephen A.; Dean, Elio (Colorado School of Mines. Arthur Lakes Library, 2018)
    Wells that produce less than 10 barrels of oil per day account for up to 96% of the Illinois Basin’s (ILB) total production. Little has been done to study the potential exploitation of unswept mobile or immobile oil through improved recovery in the Illinois Basin in a systematic field-by-field study. Department of Energy (DOE) data resource appraisals indicate that 2 billion barrels of bypassed mobile oil and more than 5.4 billion barrels of immobile oil are potential targets for future exploitation in the Illinois Basin. Heterogeneities in the basin’s reservoirs and standardized well spacing account for the failure to produce this otherwise mobile oil. This Master’s Thesis helps to better understand the opportunities that mature fields of the Southern Illinois Basin provide to produce new resources. Mode field in the central ILB is chosen as a typical marginal field that has produced around 440,000 bbls of oil to date and has estimated remaining recoverable reserves of over 970,000 bbls of oil. This study looks at the structural and stratigraphic nature of reservoirs and seals, the economic value of the field and establishes a basis of comparison for other mature fields in the ILB. The present reservoir targets are the Bethel, Benoist (Yankeetown), and Aux Vases Sandstones, however, reservoir heterogeneities require the use of new technology and new approaches to well placement to remobilize unswept oil to enhance long-term production. New opportunities for missed pay, deeper reservoir existence, and source-rock reservoir plays in the New Albany shale are also analyzed for additional oil recovery. The result of this work helps to better understand the data needs, knowledge needs and economic needs to recover future reserves in these ILB marginal fields.

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