Browsing by Subject "Methane"
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Item An Experimental Study into the Ignition of Methane and Ethane Blends in a New Shock-tube Facility(2011-02-22) Aul, Christopher Joseph ErikA new shock tube targeting low temperature, high pressure, and long test times was designed and installed at the Turbomachinery Laboratory in December of 2008. The single-pulse shock tube uses either lexan diaphragms or die-scored aluminum disks of up to 4 mm in thickness. The modular design of the tube allows for optimum operation over a large range of thermodynamic conditions from 1 to 100 atm and between 600-4000 K behind the reflected shock wave. The new facility allows for ignition delay time, chemical kinetics, high-temperature spectroscopy, vaporization, atomization, and solid particulate experiments. An example series of ignition delay time experiments was made on mixtures of CH4/C2H6/O2/Ar at pressures from 1 to 30.7 atm, intermediate temperatures from 1082 to 2248 K, varying dilutions (between 75 and 98% diluent), and equivalence ratios ranging from fuel lean (0.5) to fuel rich (2.0) in this new facility. The percentage by volume variation and equivalence ratios for the mixtures studied were chosen to cover a wide parameter space not previously well studied. Results are then used to validate and improve a detailed kinetics mechanism which models the oxidation and ignition of methane and other higher order hydrocarbons, through C4, with interest in further developing reactions important to methane- and ethane-related chemistry.Item Co-optimization of CO₂ sequestration and enhanced oil recovery and co-optimization of CO₂ sequestration and methane recovery in geopressured aquifers(2011-08) Bender, Serdar; Jablonowski, Christopher J.; Sepehrnoori, Kamy, 1951-In this study, the co-optimization of carbon dioxide sequestration and enhanced oil recovery and the co-optimization of carbon dioxide sequestration and methane recovery studies were discussed. Carbon dioxide emissions in the atmosphere are one of the reasons of global warming and can be decreased by capturing and storing carbon dioxide. Our aim in this study is to maximize the amount of carbon dioxide sequestered to decrease carbon dioxide emissions in the atmosphere and maximize the oil or methane recovery to increase profit or to make a project profitable. Experimental design and response surface methodology are used to co-optimize the carbon dioxide sequestration and enhanced oil recovery and carbon dioxide sequestration and methane recovery. At the end of this study, under which circumstances these projects are profitable and under which circumstances carbon dioxide sequestration can be maximized, are given.Item CO2 Sequestration Enhances Coalbed Methane Production(2013-05) Pang, Yu; Soliman, Mohamed Y.; Sheng, James; Menouar, Habib K.; House, Waylon V.Since 1980s, petroleum engineers and geologists have conducted researches on Enhanced Coalbed Methane Recovery (ECBM). During this period, many methods are introduced to enhance the production of coalbed methane. One of the methods called CO2-ECBM, which is injecting CO2 into the coal seam to replace the coalbed methane adsorbed on the surface of coal matrix, attracted attention of many engineers. Injecting CO2 into coalbed formation serves a dual-purpose of enhancing production while sequestrating CO2. Nowadays, CO2 emission has been identified as major contributor to global warming effect which results in climate change. Therefore, in order to eliminate the detrimental effect of global warming, finding a way to permanently store venting CO2, at the meanwhile, to enhance the coalbed methane production thereby offset the cost of CO2 sequestration may be the best strategy for both environmental protection and petroleum industry. Researches for improving methane production by gas flooding, such as performance of CO2, N2 and fuel gas injection, changes in permeability and porosity caused by gas injection due to effects of swelling and shrinkage of coal and influence of coal rank have been done. Published papers had illustrated that CO2 sequestration to enhance coalbed methane production is feasible and practical. However, well completion is seldom taken in account. Thus, this thesis not only analyzes the effects of CO2 sequestration, but also focuses on determining the efficiency of CO2-ECBM, when applying hydraulic fracturing and horizontal well techniques as well completion. Through simulation works, the thesis evaluates production of coalbed methane from the reservoir applied CO2 sequestration and provides efficient and commercial well completion alternatives for production enhancement under CO2 sequestration condition.Item Determining the Fate of Methane Released from the Seafloor in Deep and Shallow Water Environments(2014-08-12) Du, MengranMarine gas seeps and accidental marine oil spills are sources of methane (CH_(4)) to the ocean, and potentially to the atmosphere, though the magnitude of the fluxes and dynamics of these systems are poorly defined. For example, the ultimate capacity of aerobic CH_(4) oxidation, a process converting CH_(4) to carbon dioxide (CO_(2)) and biomass in most ocean waters, is unknown. Deeper water environments may provide a longer conduit for CH_(4) to transit before atmosphere emission and thus a higher likelihood for an oxidative fate. Shallow water environments may provide a shorter conduit for CH_(4) to transit before being emitted to the atmosphere, however, these environments often have some of the highest rates of primary production causing pCO_(2) to be undersaturated. Thus the biochemical conversion of CH_(4) to CO_(2) may not enable this released carbon to be emitted to the atmosphere. To better constrain these variables in natural environments, studies of dissolved oxygen (DO) concentration, CH4 concentration and stable isotopic ratios were conducted at two contrasting sites: the Deepwater Horizon (DWH) oil spill in the Gulf of Mexico (GoM) and the natural seep field near Coal Oil Point (COP), CA. The investigation of 1316 DO profiles measured from 11 May until 20 September 2010 revealed the spatial and temporal variability of bulk hydrocarbon respiration in these deep and intermediate plumes since DO is removed during hydrocarbon respiration. These analyses suggest that the general movement of these plumes was toward the southwest, and that a total mass of 0.18?0.05 Tg hydrocarbon in the plume layers was fully respired to CO_(2), and 0.10?0.08 Tg hydrocarbon was incorporated into biomass (i.e. conversion efficiency 0.36?0.11 mg biomass/mg hydrocarbon). A stable isotope model incorporating measurements of CH_(4) concentrations, CH_(4) oxidation rates, and current velocity was developed to determine CH_(4) oxidation rates, as well as the flow rate from the seafloor. This model was tested on 20 samples taken from 1 to 12 km from the wellhead from 11 June through 20 June 2010 during the DWH oil spill. Results suggest that the rate of CH4 oxidation ranged from 22 to 844 nM d^(-1) in mid-June 2010 and that the rate of flow from the Macondo well was 8.4?10^(7) moles d^(-1), both of which are in agreement with previous estimates determined independently. High-resolution measurements of sea surface CH_(4) and CO_(2) concentrations and air-sea fluxes were conducted at the COP seep field. Results suggest that the diffusive air-sea fluxes of CH_(4) and CO_(2) were 0.18?0.19 mmol m^(-2) day^(-1) and -1.65?1.23 mmol m^(-2) day^(-1), respectively, and that the extent of microbial oxidation of CH_(4) was insufficient to change this shallow water environment from a sink of atmospheric CO_(2) to a source. The seeps at COP released CH_(4) into waters at a rate that was an order of magnitude less than that from the DWH oil spill, and resulted a plume area that was also an order of magnitude less. In total, these results suggest that microbial oxidation provides the dominant sink of the released CH_(4) at both sites.Item Diurnal variations in methane emission from rice plants(Texas A&M University, 2004-11-15) Laskowski, Nicholas AaronA greenhouse study was conducted to investigate the mechanisms causing diurnal variations in methane emission from rice plants (Oryza sativa L.). Methane emission was measured using a closed chamber system on individual rice plants at five stages of development. The role of the rice plant as the primary methane transport component was examined by comparing emission from intact plants to plants severed above and below the water. No diurnal variations were present in the severed plants and the emission was greatly reduced when compared to the intact plant. Results from the vascular transport experiment showed that transpiration is a major factor in methane emission. Emission dependence on soil temperature was examined to test the hypothesis that soil temperature affects emission. With some plants, soil temperature was held constant using a water bath, otherwise the soil temperature was allowed to vary with environmental conditions in the greenhouse. Diurnal variations in emissions were higher for plants with uncontrolled soil temperature than for plants with controlled soil temperature. Soil temperature at a 5 cm depth explained 46% of the emission variation. Soil temperature affects the source of methane in the soil while transpiration promotes the uptake of water and subsequently the emission of methane. Methane emission was negatively correlated with biomass, probably due to effects of root biomass on soil water methane concentration. Methane concentration in soil water was negatively correlated with root biomass, most likely due to increases in soil oxidation with increasing biomass in a fixed soil volume, and change in root conductance with age.Item Effect of a discrete three-phase methane equilibrium zone on the bottom-simulating reflection(2016-12) Shushtarian, Arash; Daigle, HughMarine gas hydrates are stable under conditions of low temperature and high pressure in the upper few hundreds of meters below the seafloor in a variety of geological setting. At a discrete horizon where thermodynamically favored phase switches from hydrate to gas, a characteristic seismic reflection referred as the bottom-simulating reflection (BSR) is produced. Furthermore, in sediments with a distribution of pore sizes, the gas and hydrate phases can coexist in pores of different sizes, giving a rise to three-phase equilibrium zone. This three-phase zone causes the BSR to have distinct characteristics that differ from those observed with a discrete phase boundary. The main objective of this thesis is to model the seismic response of a potential three-phase zone at the Walker Ridge Block 313H in the northern Gulf of Mexico. I modeled the BSR arising from this three-phase zone and analyzed the characteristics of the BSR and their relationships to the thickness and phase saturation within the three-phase zone. This was done by determining the elastic properties of the formation via rock physics models and their mathematical convolution with a seismic wavelet to create synthetic seismograms. Results show that the main factor for the intensity of the BSR is the abundance of the free gas in the three-phase zone. Free gas saturation as low as 5% in the three-phase zone is enough to make the BSR visible in synthetic seismograms regardless of the hydrate saturation. Results of this thesis are significant for resource prospecting based on seismic data, drilling hazard identification, as well as the importance of hydrate as a potential source of energy and its influence on the global climate. For seismic prospecting, the presence of a three-phase zone inferred from BSR characteristic indicates the minimum methane flux into the base of the hydrate stability zone, and can be used to infer whether sufficient methane is available to form hydrate. For drilling hazard identification, the BSR characteristic indicates a possible shallower occurrence of gas than would be estimated under the assumption of a discrete phase boundary.Item Effect of additives on anaerobic methane production(Texas Tech University, 1998-05) Sastry, RadhicaAnaerobic digestion is widely known as a method of treatment of wastewater. Present technology, however, is able to achieve only partial degradation of waste. Increases in the cost of sludge disposal, and in the treatment process itself, has motivated many researchers to look for ways to improve the efficiency of the treatment process. Biocatalysts or other commercial additives are compounds that are capable of altering the rate of reactions of some microbial systems. Use of these compounds is a new innovation in wastewater treatment technology. Five commercial additives were added to anaerobic reactors containing primary municipal wastewater sludge loaded with 3% volatile solids. The additives were added in duplicate reactors and two reactors were maintained as control reactors. The effect of each of the additives on the treatment process was studied by the analysis of various biological and chemical parameters. It was found that only two additives made a statistically significant difference (p<0.05) to the treatment process. The addition of Biocope™ caused an increase of 7% in the volatile solids destruction, while the addition of MPC caused a decrease of 8% in the volatile soHds destruction as compared to the control. The volatile solids reduction achieved by the remaining three additives was not significantly different from the control. It was also found that all the additives, except Medina, resuhed in a decrease in biogas production. The volume of biogas produced due to the addition of Medina was not significantly different from the control. The addition of Biocope™ and Aiken resuUed in a 74% decrease in the volume of biogas produced as compared to the control.Item The effect of restrictive diffusion on hydrate growth(2016-05) Andris, Ryan Gerald; Daigle, Hugh; Mohanty, KishoreMethane hydrate is formed naturally in a number of geologic settings around the world. The most predominant methane hydrate reservoirs are found in shallow oceanic basins at low temperatures and high pressures. A widely observed phenomenon in these oceanic sequences is extensive fine-grained sediments containing little to no hydrate interbedded with highly saturated sand bodies (20-60%). At Walker Ridge Block 313 in the Gulf of Mexico, one particular coarse-grained bed (approximately 3m-thick) is estimated to have methane hydrate occupying as much as 60% of the available pore space surrounded by hydrate-free clay. Here, I develop a numerical model that simulates methane hydrate growth in shallow oceanic basins in order to test whether diffusive transport of methane is a viable transport mechanism for forming highly saturated sand layers. I conclude that methane diffusion is likely responsible for the key identifying features of hydrate formation in interbedded sands and shales (i.e. greater hydrate saturations at the sand boundaries surrounded by hydrate-free zones in the fine-grained matrix). In addition, I show that the key parameters affecting the hydrate saturation profile include the amount of available methane for hydrate growth, thickness of the sand layer, and the radius of the fine grained pore space. I also discuss the shortcomings of the developed model and what complexities need to be added to more accurately reproduce hydrate growth throughout intricate hydrogeologic systems.Item Effects of simulated inundation on wetland methane flux predictions for the southeastern U.S.(2015-08) Resovsky, Alex Edward; Yang, Zong-liang; Shanahan, Timothy M; Breecker, Daniel OThis work provides an overview of factors that influence methane emissions from natural wetlands in the southeastern U.S. at seasonal and interannual timescales. It then examines simulations using CLM4Me, a methane biogeochemistry model run within CESM, through comparison with recently compiled flux estimations from remote sensing data. In addition, we assess how seasonal methane flux simulations in CLM4Me are affected by the use of alternative estimates of inundated land fraction. Inundation predictions are provided by DYPTOP, a TOPMODEL implementation which can be used to simulate the dynamics of wetland spatial distribution. Results may aid in future model development and in understanding the role of subtropical and temperate North American wetlands under future climate projections.Item Explosion dynamics of van der Waals clusters using 38 nm XUV laser pulses(2016-08) Helal, Ahmed Mohammed; Ditmire, Todd; Keto, John W.; Bengtson, Roger D; Downer, Michael; Ben-Yakar, AdelaThe interaction of intense XUV laser pulses with matter and rare gas cluster has been the focus of the scientific c community for decades. This focus has been sparked by the ongoing efforts to reach microscopy with atomic resolution, leading to a time resolved image on the scale of the atomic motion. The interest in van der Waals clusters appears due to it's similarity with the small bio-molecules, studying the behavior of these cluster will shed some light on how the biomolecules behavior under intense laser pulse. We have conducted a major upgrade to the UT THOR laser system, that enables us to achieve 17.7 nJ of XUV energy, produced by high harmonic generation, which is used to conduct multiple cluster experiments. We investigated the dynamics of rare-gas clusters produced by Ar and Xe gases, the ion time of flight, kinetic energy and electron energy have been measured, the generation of ion kinetic energy of two di different temperatures (6 and 55 eV) due to hydrodynamic expansion was observed. viii For Xe clusters, we observed the generation of unexplained high charge states up to Xe^9+, that could be due to the effect of continuum lowering and inner ionization of the giant resonance 4d-level. We also investigated the dynamics of small molecule clusters. Stating with nitrogen clusters, we noticed a dependence of the ionization ratio between N+ 2 and N+on the cluster size has been noticed. In addition to that nitrogen clusters shows the highest ion kinetic energy generated between all the clusters investigated in this dissertation. The interaction of XUV laser pulses with Methane cluster is studied, we could not detect any high charges of methane fragments such as (CH2+ 4 ). However, we noticed that we generated multiple fragments by breaking C-H bonds (CH+3 ;CH+ 2 ;CH+) in addition to bare carbon with high cluster sizes. The generation of CH+5 , H+ and H+2 was also observed. Studying the partial yield of each of these reveals that the correlation between CH+ 5 and H+ is opposite to what is expected, which might be due to the change of the cluster properties or the expansion dynamic itself (towards more hydrodynamics).Item Fracture-permeability development in organically-rich sediments through methane generation(Texas Tech University, 1999-12) Monroe, John NapierThe result of methane generation in low-permeability rock matrices is fracturepermeability development. Such expansion is the result of methane generation which, in turn, is the result of burial of organic matter under euxinic conditions. The fracturepermeability-development process has been demonstrated in the laboratory using a microwave oven to generate gas (water vapor) in well-indurated, low-permeability sedimentary rocks. The process has been quantified through modeling constrained by principles of chemistry and physics. The modeling process is applied to both shales and limestones and relates sediment expansion to sediment organic carbon content converted to methane. The model shows that the quantity of organic carbon required to be converted into methane for microfracture development is small compared to the amount commonly contained in hydrocarbon source rocks. A wide variety of fracture-producing mechanisms proposed to explain natural fracture development in hydrocarbon reservoirs is acknowledged. However, fracturepermeability-development that appears to occur selectively in low-permeability, organically-rich sequences has received much less attention. Additionally, unabsolved anomalies that persist when current explanations are applied call attention to the need for alternative explanations. The fracture permeability, including the distribution and orientation of those fractures, which some reservoirs exhibit seem to defy explanation until now. A better understanding of fracture-permeability development and related aspects of petroleum maturation will remain illusive until the methane-generation fracture-permeability process, which until now has not been adequately quantified, is fully appreciated. Sediment expansion through methane generation in low-permeability rock matrices explains fracture-permeability development in many naturally-fractured hydrocarbon reservoirs including cleat permeability in coalbed methane reservoirs. Evidence is presented for the importance of this fracture permeability process in producing the natural fractures in low-permeability matrix sediments ofthe Frio Formation (Oligocene); i.e., the Frio Formation's geopressured shales; and the low-permeability matrix sediments ofthe Spraberry Formation (Leonardian), the Clear Fork Formation (Leonardian), the Strawn Formation (Pennsylvanian), and the Austin Chalk Formation (Upper Cretaceous).Fracture-permeability development through methane generation is of utmost importance to the migration of liquid and gaseous hydrocarbons out of source beds into reservoir beds.Item Geochemical effects of elevated methane and carbon dioxide in near-surface sediments above an EOR/CCUS site(2013-05) Hingst, Mary Catherine; Young, Michael H.; Romanak, Katherine DunckerCarbon capture, utilization and storage (CCUS) aims to reduce CO₂ emissions by capturing CO₂ from sources and injecting it into geologic reservoirs for enhanced hydrocarbon recovery and storage. One concern is that unintentional CO₂ and reservoir gas release to the surface may occur through seepage pathways such as fractures and/or improperly plugged wells. We hypothesize that CO₂ and CH₄ migration into the vadose zone and subsequent O₂ dilution and Eh and pH changes could create an increased potential for metal mobilization, which could potentially contaminate ground and surface waters. This potential has not been addressed elsewhere. Goals of this study are to understand how the potential for metal mobilization through soil pore water may increase due to CO₂ and CH₄ and to assess potential impact to aquifers and/or the biosphere. The study was conducted at a CCUS site in Cranfield, MS, where localized seepage of CH₄ (45%) from depth reaches the surface and oxidizes to CO₂ (34%) in the vadose zone near a plugged well. Four sediment cores (4.5-9m long) were collected in a transect extending from a background site through the area of anomalously high soil gas CO₂ and CH₄ concentrations. Sediment samples were analyzed for Eh and pH using slurries (1:1 vol. with DI water) in the field and for occluded gas concentrations, metal (Ba, Co, Cr, Cu, Fe, Mn, Ni, Pb and Zn) concentrations, moisture content, organic carbon content, and grain size in the laboratory. Data from the background reference area (no gas anomaly: occluded gas ~21% O₂, <1% CO₂, 0% CH₄) showed oxidized conditions (Eh from 464-508mV) and neutral pH (7.0-7.8) whereas samples collected near the gas anomaly (13-21% O₂, 0.1-5% CO₂, <0.1% CH₄) were more reducing (Eh 133-566mV) and more acidic (pH = 5.3-8.0). Significant correlations were found between Eh and O₂ (r = 0.95), pH and CO₂ (r = -0.88), and between these parameters and acid-leachable metals in samples from within the soil gas anomaly. Correlations quickly weaken away from the anomaly. Statistically, total metal concentrations, except for Ba, are similar in all cores. Acid-mobile metal concentrations, above 5m, increase toward the gas anomaly. The percent of water-mobile metals is very low (<2%) for all metals in all cores, indicating freely-mobile metals are not affected by elevated CO₂/CH₄. Conclusions are: 1) oxidation of CH₄ to CO₂ depletes O₂ causing reducing conditions; 2) high CO₂ and low O₂ affect Eh and pH of sediments which in turn alters mineralogy and bond strength between sediments and adsorbed ions; 3) intrusion of strongly acidic fluids (pH of acid used was 0.39) into these sediments could potentially remove weakly bonded metals or dissolve minerals. Implications from this study are that Eh needs to be considered along with pH when analyzing contamination potential, and that exposure of sediments to reducing, followed by acidic conditions, increases the potential for metal mobilization in the vadose zone. More research is needed to determine the concentration of gases (CO₂, CH₄ and O₂) that will create Eh and pH levels that could affect the mineralogy and sorption mechanism potentially leading to metal mobilization. Methods for assessing potential metal mobilization may be useful for site characterization and risk assessment.Item Methane detection by He-Ne laser for oil and natural gas prospecting(Texas Tech University, 1984-05) Jordan, Kevin JamesSurface geochemistry studies are valuable methods of petroleum prospecting. Atmospheric methane surveys can outline those areas where detailed geochemical studies need to be conducted. This report describes a field device capable of measuring small changes in methane concentration in the near surface atmosphere. Methane concentration is determined by measuring the attenuation of the 3.3922y He-Ne line in a pressurized gas flow cell due to absorption by methane. A second He-Ne laser line at 3.3912 p, which is only weakly absorbed by methane, is used as a reference signal to compensate for laser intensity fluctuations and scattering by water and dust. This system s fast, allowing measurements to be made from a moving vehicle- Also, the system allows for continuous sampling of the changing methane concentration as opposed to point measurements.Item Methanol production by direct oxidation of methane in a plasma reactor(Texas Tech University, 1998-08) Mooday, RickMethanol is one of the most widely-produced chemicals in the world. It is a key raw material in the production of many chemicals in the petrochemical industry. Methanol also has vast potential for expanded applications as a fuel. It is currently produced by an energy intensive and expensive two step process. An economically feasible one step process could significantly reduce methanol production cost, saving millions of dollars. A methane-to-methanol process, built at remotely located methane reserves, would convert methane into a different energy form that is much easier to transport. This would make methane a much more attractive and valuable energy source. The purpose of this investigation was to evaluate the feasibility of producing methanol by direct oxidation of methane using a plasma reactor. The chemistry of methane oxidation is well understood and free radicals play a central role in methane oxidation reactions. Low pressure experiments by other researchers indicated that methanol can be produced by direct oxidation of methane in plasma reactors. However, the viability of a plasma-based methanol production process depends on its ability to convert large quantities of methane. This work was directed at plasma reactor operation near atmospheric pressure to increase the amount of material processed. The focus of this mvestigation was the design and construction of an experimental apparatus which could achieve methanol synthesis in a plasma reactor by direct oxidation of methane at atmospheric pressure. A microwave source provided the energy to generate the plasma. The system was designed to study the effects of reactant concentration and flow configurations on methanol production. Since high levels of methanol selectivity are the primary consideration in direct synthesis of methanol from methane, improvements in methanol selectivity were desired. The objective of the four experimental phases was to investigate reactor operating conditions and improve methanol production and selectivity. Methanol production at atmospheric pressure was demonstrated in this plasma system and steady improvements in methanol selectivity were achieved as the investigation proceeded. Experiments showed that high concentrations of water and low concentrations of oxygen improved methanol selectivity. In the last experimental phase, oxygen was divided into both reactant streams, but this approach did not improve methanol production. It was observed that higher methanol selectivities were obtained only at low methane conversions. As in other plasma studies, methanol production did not approach what would be required for commercial feasibility.Item Molecular Weight of Condensed Tannins from Warm-season Perennial Legumes and Its Effect on Condensed Tannin Biological Activity(2013-05-21) Naumann, Harley DeanCondensed tannins (CT) are polyphenolic compounds that have demonstrated biological activities in ruminants including suppression of enteric methane (CH4) production, protein binding and suppression of gastrointestinal nematode (GIN) infections. Some forage CT have been reported to be biologically active, whereas others have demonstrated no biological activity at all. While the chemical structure of CT has been postulated to be a key contributing factor affecting biological activity, the specific factors that determine whether or not CT from a specific forage have bioactive properties remain unknown. Results from previous studies have shown that as molecular weight of CT increases, CT biological activity also increases. Others have reported no effect of CT molecular weight on biological activity. The relationship between molecular weight of CT and CT biological activity remains inconclusive. The effect of molecular weight of CT from a variety of warm-season perennial legumes commonly consumed by ruminants on biological activity has not been adequately explored. The objectives of this study were to determine if molecular weight of CT from warm-season perennial legumes could predict the biological activity of CT relative to suppression of enteric CH4 production, protein-binding ability (PB) and anthelmintic activity, and to compare the biological activity of CT from native warm-season perennial legumes to that of the introduced species Lespedeza cuneata, a plant that has gained attention in recent years due its anthelmintic properties. All or a combination of the following warm-season perennial legume species were evaluated for in vitro gas production, protein-precipitable phenolics (PPP) and PB, and percent larval migration inhibition (LMI). Eight North American native warm-season perennial legumes: Leucaena retusa Benth. (littleleaf leadtree), Desmanthus illinoensis (Michx.) MacMill. Ex B.L. Rob. & Fernald (Illinois bundleflower), Lespedeza stuevei Nutt. (tall lespedeza), Mimosa strigillosa Torr. & A. Gray (powderpuff), Neptunia lutea (Leavenworth) Benth. (yellow puff), two ecotypes of Acacia angustissima var. hirta (Nutt.) B.L. Rob (prairie acacia), Desmodium paniculatum (L.) DC. var. paniculatum (panicledleaf ticktrefoil), and two introduced legumes: Arachis glabrata Benth. (rhizoma peanut) and Lespedeza cuneata (Dum. Cours.) G. Don (sericea lespedeza) were included. In vitro CH4 production regressed on CT MW resulted in a R2 of 0.0009 (P = 0.80). There was no correlation between PPP or PB and MW of CT (R^2 0.11; P = 0.17 and R^2 0.02; P = 0.54, respectively). There was a weak correlation between CT MW and percent LMI (R^2 0.34; P = 0.05). The results of our study strongly suggested that CT MW does not explain the biological activities of enteric methane suppression or protein-binding ability. Condensed tannin MW may be involved in anthelmintic activity of CT from the forage legumes surveyed. North American native legumes containing biologically active CT, as compared to introduced species, were identified as having promise for use in ruminant diets.Item Numerical prediction of mixing process in a methane-fueled engine(Texas Tech University, 1993-05) Arici, Mehmet EminOne of the most important factors controlling the combustion process within internal combustion engines is the charge mixing. The charge mixing process in a gaseous fueled engine is different than that in a liquid fueled engine. In a conventional liquid fueled engine, the liquid fuel goes through the process of vaporization before the gaseous mixing takes place. Gaseous fuels, on the other hand, are already in a vapor form and do not go through the vaporization process. Among the gaseous fuels, natural gas, which consists of about 90% methane, is gaining acceptance because of its low emission levels and alternative energy source concerns. Introducing methane into the conventional spark ignition engine intake system causes about a 10% engine power loss contributed by low density of the fuel. By introducing natural gas directly into the engine cylinder, this power loss can be reduced. The present work concerns numerical prediction of in-cylinder methane/air mixing preparation. A computer-based solution procedure, which employs a finite-difference solution of general conservation equations of motion in a piston/cylinder assembly, has been developed to predict the fuel/air mixing characteristics. This solution procedure has been used as a predictive tool to investigate the dependence of charge mixing characteristics on the flow field in the absence of combustion. Computational results show that the flow field has a great effect on charge mixing. The fuel/air mixing characteristics at the time of initiation of combustion are satisfactorily close to the mixing requirements when the fuel charging is prescribed properly.Item Pressure transient testing in coalbed methane reservoirs(Texas Tech University, 1997-05) Mahendra, Sumil K.Pressure transient testing in coalbed methane reservoirs differs significantly from well testing in conventional gas reservoirs. Coal's storage and production mechanisms are the primary cause for the disparity in the analysis for the two types of reservoirs. A modification of conventional analysis methods is required, at most times, to adequately evaluate a coal reservoir. This study characterizes a dewatered coal gas reservoir at a specific test site through evaluation of pressure responses from the coal wells in the area. Three different analysis techniques, namely, single-well test analysis, multi-well test analysis and reservoir simulation, were employed to estimate the reservoir properties for the formation at the site. Additionally, the intent of this study was to identify the well testing model representative of the pressure response from a coal reservoir. The real gas pseudopressure method was employed for single- and multiwell test analysis using PIE, a well testing software. Some multi-well test analysis was also performed using Papadopulos-Ramey method, which is specifically designed for anisotropic formations. The reservoir simulation portion of the study, for evaluation of multi-well test analysis results, was performed on ECLIPSE-200, a coalbed methane simulator. Single- and multi-well test analysis of the pressure transient tests run on the coal wells at the site suggested a homogeneous and radial reservoir with boundary effects. This conclusion was reached despite the fact that coal is a dual porosity and dual permeability reservoir. Single- and multi-well test analysis also suggested scale dependent permeability and partially sealing no-flow boundaries at the formation site. Additionally, an average geometric mean permeability was determined for the site from multi-well test analysis. Reservoir simulation gave an estimate for the directional orientation of the face and butt cleat systems, and a measure of the anisotropic permeability ratio between the face and butt cleats for the tested site. Future work needs to be done to determine the exact location of the noflow boundaries and the orientation of the face and butt cleat systems.Item Radiochemical Transformation of High Pressure Methane under Gamma, Electron, and Neutron Irradiation(2014-05-01) Clemens, Jeffrey TylerThe chemical effects of irradiation on high pressure methane and noble gas mixtures were investigated using gamma, electron beam, and neutron irradiation sources. The gamma source used was the La-140 source from the Nuclear Science Center (NSC) at an activity of 400 Ci. The electron source was a 10 MeV, 15 kW, linear accelerator at the National Center for Electron Beam Research. The neutron source was the NSC reactor running at 1 MWth. The in-core positions were used for the neutron irradiations had neutron fluxes ranging from 5 x 10^(12) to 1x10^(13) n/cm^(2)/s. The gases used for the study included research grade methane, argon, and helium. The compressed gases were irradiated in a several separate irradiation vessels made with minimal nonmetal parts to reduce contamination. The majority of the vessels were pressurized to 2.07 MPa (300 psi) for the irradiation. The vessels were irradiated by one of the three irradiation sources for a maximum dose. The methane was mixed with the noble gases helium and argon, these gases were added to dilute the methane concentration, and study charge transfer effects on radiation chemical yields. The reaction products were measured using a gas chromatography mass spectrometer (GCMS). In addition to the GCMS, a lab made mass spectrometer system was used to measure the hydrogen and ethane concentrations within the gas post irradiation. The NSC Reactor irradiations show a measurable increase in the concentration of ethane and hydrogen, the La-140 and electron beam irradiations do not show measurable increases in hydrogen and ethane concentrations. The primary accomplishment of this research was the design of systems that are capable of performing high pressure gas irradiations. The irradiation experiments devel-oped three separate irradiation vessels during the course of the experiments. The analysis system was a mass spectrometer system that is capable of trace molecule detection. The experiments that had shown measurable change in the hydrogen and ethane concentra-tions had the G-values of the individual reaction products calculated for the NSC reac-tion irradiations. The G-values for were calculated to be 2.61?0.62 and 1.16?0.34 for hydrogen and ethane production, respectively. The effects of different types of radiation were examined during this thesis, and a future experimental work is proposed.Item The role of methane in limiting CO₂ EOR : case study of offshore Gulf of Mexico oil reservoirs(2015-05) Ogbuabuo, Prisca Chinwendu; Lake, Larry W.; Smyth, Rebecca C. (Rebecca Chappell), 1957-; Fisher, William LData from the US Department of Interior - Bureau of Ocean and Energy Management - 2012 Offshore Gulf of Mexico Atlas were analyzed to: (i) compute reconnaissance-level estimates of CO₂ volumes for storage in sub-seabed offshore Gulf of Mexico (GoM) oil sands before and after carbon dioxide (CO₂) enhanced oil recovery (EOR), (ii) investigative technical and economic impacts of CO₂ injection in gas-rich offshore GoM hydrocarbon fields, and (iii) analyze legal issues and framework associated with offshore geologic sequestration or storage (GS). Part (i) of this study, Reconnaissance-level estimation of CO₂ sub-seabed GS potential in offshore GoM, builds on a similar study conducted by The University of Texas at Austin, Bureau of Economic Geology on potential onshore CO₂ GS in the GoM region, published in Nunez-Lopez et al. (2008). Part (ii) focuses on the use of two screening methodologies to investigate the impact of native methane (CH₄) in recycled CO₂. The impact of CH₄ on the effectiveness of CO₂ as a solvent for EOR is defined by: Calculating minimum miscibility pressure (MMP) of pure CO₂ for each oil sand (conventional oil reservoirs), Computing impure CO₂ MMP for each oil sand considering only native CH₄ as an impurity and neglecting other trace gas components in the oil reservoir. Five to 50 mole percent CH₄ impurity factor was computed as a function of the pseudocritical temperature (T[subscript pc]) of the CH₄-CO₂ mixture. Plotting miscibility against sub-seabed depth, total depth, play type, and API gravity. Part (iii) analyzes existing US outer continental shelf (OCS) regulations under the authority of the US Department of the Interior stated in Title 30 CFR Part 250 and Part 550 to determine their applicability to carbon capture, offshore GS, and CO₂ EOR. The study results show a potential storage capacity of approximately 3.5 billion metric tons of CO₂ after CO₂ EOR for the 3,598 offshore GoM individual oil sands assessed in Part (i). For Part (ii), results indicate that deeper reservoirs are most tolerant to miscible impure CO₂ EOR. Of the play types defined by the BOEM, fan and fold belt plays are most tolerant to impure CO₂ flooding. Further study on the impact of impure CO₂ on MMP resulted in a definition of 18 mole percent as the cutoff for economic and technically viable CO₂ flooding in offshore GoM oil fields. When a hypothetical CO₂ injection stream exceeded 18 mole percent CH₄ contamination, 72% of the case study oil reservoirs became immiscible. In Part (iii), policies that address offshore CO₂ GS, CO₂ EOR, and both price based and non-price based mechanisms in the OCS would accelerate a shift towards implementing GS and CO₂ EOR in offshore GoM.Item The technical potential of renewable natural gas (RNG) in the United States, and the economic potential of methanation-derived RNG in Texas(2014-12) Ólafsson, Brynjólfur Víðir; Webber, Michael E., 1971-Renewable Natural Gas (RNG) is a low-carbon fuel source that is derived from the anaerobic digestion (AD) or thermal gasification (TG) of biomass, or produced using renewable electricity through the methanation of carbon dioxide. This thesis uses a thermodynamic balance to determine the total technical potential of RNG in the United States, as well as the future technical potential of methanation-derived RNG based on growth curves for renewable electricity. Furthermore, this work establishes an analytic decision-making framework for determining on a rolling basis, from an economic standpoint, whether to sell electricity directly to the grid, or produce and sell methanation-derived RNG. This framework is used to establish the economic potential of RNG, based on Texas wind resources. This work details the formulation of a model that determines which production option generates more marginal profit, based on fluctuating electricity and gas prices. The model also aggregates the total amount of electricity and RNG sold, assuming that the main objective is to maximize the marginal profit of integrated wind- and methanation facilities. This work concludes that the annual technical potential of methanation-derived RNG nationally was 1.03 Quads in 2011. The technical potential of biomass-derived RNG was 9.5 Quads. Thus, the total 2011 technical potential of RNG in the United States was 10.5 Quads, or equal to roughly 43% of the total US consumption of natural gas that year. Assuming a constant, 80% electrolyser efficiency, the technical potential of methanation-derived RNG is expected to rise at an average rate of 1.4% per year, following growth curves for renewable power, until the year 2040, when it will be 1.54 Quads. The 2011 economic potential of methanation-derived RNG in Texas was between 2.06×10⁷ MMBTU and 3.19×10⁷ MMBTU, or between 19.4% and 30.1% of the corresponding annual technical potential. Furthermore, the total marginal profit increase from introducing the option of producing and selling methanation-derived RNG was around $366 million, given a ‘best case scenario’ for the state of Texas.