Browsing by Subject "Analytical"
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Item Analytical and Numerical Solutions for the Case of a Horizontal Well with a Radial Power-Law Permeability Distribution--Comparison to the Multi-Fracture Horizontal Case(2013-02-08) Broussard, Ryan SawyerIn this work, I present the development of analytical solutions in the Laplace domain for a fully-penetrating, horizontal well producing at a constant flow rate or constant wellbore pressure in the center of a composite, cylindrical reservoir system with an impermeable outer boundary. The composite reservoir consists of two regions. The cylindrical region closest to the wellbore is stimulated, and the permeability within this region follows a power-law function of the radial distance from the wellbore. The unstimulated outer region has homogeneous reservoir properties. The current norm for successful stimulation of low permeability reservoir rocks is multi-stage hydraulic fracturing. The process of hydraulic fracturing creates thin, high permeability fractures that propagate deep into the reservoir, increasing the area of the rock matrix that is exposed to this low-resistance flow pathway. The large surface area of the high conductivity fracture is what makes hydraulic fracturing so successful. Unfortunately, hydraulic fracturing is often encumbered by problems such as high capital costs and a need for large volumes of water. Therefore, I investigate a new stimulation concept based upon the alteration of the permeability of a large volume around the producing well assembly from its original regime to that following a power-law function. I evaluate the effectiveness of the new concept by comparing it to conventional multi-stage hydraulic fracturing. The results of this investigation show that the power-law permeability reservoir (PPR) has a performance advantage over the multi-fractured horizontal treatment (MFH) only when the fracture conductivity and fracture half-length are small. Most importantly, the results demonstrate that the PPR can provide respectable flow rates and recovery factors, thus making it a viable stimulation concept for ultra-low permeability reservoirs, especially under conditions that may not be conducive to a conventional MHF treatment.Item Enzymatic inhibition-based biosensing on nitrogen-doped carbon nanotube electrodes(2015-05) Rust, Ian Matthias; Stevenson, Keith J.; Webb, Lauren JWhile previous work has demonstrated the effectiveness of nitrogen-doped carbon nanotubes (N-CNTs) as biogenic electrode materials in first- and second-generation biosensors, this thesis primarily explores enzymatic inhibition-based biosensing schemes on N-CNT electrodes. This type of scheme enables the detection of enzymatic inhibitors, as opposed to enzymatic substrates, making these inhibition-based biosensors much more suitable for the monitoring of environmental pollutants. Presented in this thesis is a biosensor which couples N-CNTs with glucose oxidase (GOx) through spontaneous physical adsorption for the highly sensitive detection of aqueous silver ions. Included is a thorough discussion of the parameters that affect response time as well the biosensor’s aptitude for repeated use. A later chapter presents initial work towards the inhibition-based detection of sucralose, a relatively new environmental pollutant. A bi-enzymatic approach is explored, in which both GOx and invertase are immobilized on an N-CNT modified electrode. Finally, shifting focus from inhibition-schemes, the last remaining chapter investigates the coupling of CNTs and N-CNTs with methylene green (MG), a redox mediator used in second-generation biosensors based on NADH oxidation. Common coupling techniques are examined for their effectiveness in decreasing the overpotential required for NADH oxidation.Item Tandem mass spectrometry approaches to characterizing challenging biomolecules : stapled and cyclic peptides and variants of lipid A from gram-negative bacteria(2016-08) Crittenden, Christopher Martin; Brodbelt, Jennifer S.; Mullins, Charles BMass spectrometry has emerged as a leading tool in the field of chemistry as an analytical method for the characterization of small molecules, proteins, and other complex biomolecules. Specifically, cyclic and stapled peptides have become an intriguing class of biomolecules in drug research afforded to them because of their biological stability and resistance to proteolytic digestions. However, challenges are presented in regards to the characterization of these molecules as traditional methods are ineffective in determining a ring-opening site on the peptidic backbone. Additionally, lipid A, the hydrophobic domain of lipopolysaccharide (LPS), consists of a diglucosamine backbone and is responsible for fastening LPS to a membrane surface. Lipid A becomes a biologically relevant molecule to study as its function within LPS is directly related to the infectious and toxic properties of gram-negative bacteria, but the molecule is structurally complex and offers many challenges in terms of traditional mass spectrometry characterization. Presented in the thesis are methods to further comprehend structural motifs related to the aforementioned biomolecules. The “ornithine effect”, which describes the conversion of an arginine residue to an ornithine residue via reaction with hydrazine and subsequent preferential cyclization via nucleophilic attack of the ornithine side-chain to the neighboring carbonyl group, inducing heterolytic cleavage of the adjacent amide bond under gentle activation, is used to preferentially open cyclic and stapled rings to linearize these challenging biomolecules. Ramped collisional and photon based activation (in terms of energy and laser pulses) of lipid A molecules that contain differences in acyl-chain length and connectivity reveal general trends about the lability of certain bonds on the lipid A molecules themselves and paints a picture of the overall fragmentation trends associated with variations in lipid A structural motifs.