17 Matching Results

Search Results

Advanced search parameters have been applied.

The Dynamics of Adsorption on Clean and Adsorbate-Modified Transition Metal and Metal Oxide Surfaces

Description: Research directed toward understanding the dynamical factors governing the adsorption of molecules typically involved in heterogeneous catalytic processes has been continued. Adsorption is the first step in any catalytic process, and predictions of rates of adsorption are fundamental to calculations of rates of catalytic reactions. Dissociative adsorption can occur either directly upon impact with the surface or as the result of the migration of a temporarily trapped species across the surface. Alkane activation exhibits both of these pathways for reaction on metal surfaces. We have focused on the dynamics of dissociative adsorption of low molecular weight alkanes on single crystal surfaces of platinum group metals. The overall objective of these studies was to make a quantitative comparison of the dissociation probabilities of C{sub 2}-C{sub 4} alkanes on different metals in order to assess the effects of the structures of the different alkanes and the intrinsic differences of the metals on reactivity. First, an unusual and somewhat unexpected difference is observed in the reactivity of linear and branched alkanes. Further, the reactivity of each alkane is significantly higher on Pt(111) than on Pd(111). It has also been observed that the trapping probabilities for the alkanes are higher on Pd(111) due to a larger dissipation of energy to lattice vibrations upon collision, suggesting that energy dissipation in the reaction coordinate into phonons may be involved in dissociative adsorption. We have thus focused on the dynamics of dissociative adsorption of low molecular weight alkanes on single crystal surfaces of platinum, palladium and nickel in order to assess the role of energy dissipation from the incident molecule and the differences of the reactivity of the different metals. We observe that the reactivity of each of the alkanes studied to date differs by only a small amount. On the contrary, due to the dissipation of ...
Date: March 31, 2006
Creator: Madix, Robert J.
Partner: UNT Libraries Government Documents Department

Experimental Investigation and High Resolution Simulator of In-Situ Combustion Processes

Description: Accurate simulation of in-situ combustion processes is computationally very challenging because the spatial and temporal scales over which the combustion process takes place are very small. In this current and fourteenth report, we report on our continued numerical experimentation with the Virtual Kinetic Cell and our continuing experimental program.
Date: March 31, 2007
Creator: Gerritsen, Margot & Kovscek, Anthony
Partner: UNT Libraries Government Documents Department

Solving large-scale sparse eigenvalue problems and linear systems of equations for accelerator modeling

Description: The solutions of sparse eigenvalue problems and linear systems constitute one of the key computational kernels in the discretization of partial differential equations for the modeling of linear accelerators. The computational challenges faced by existing techniques for solving those sparse eigenvalue problems and linear systems call for continuing research to improve on the algorithms so that ever increasing problem size as required by the physics application can be tackled. Under the support of this award, the filter algorithm for solving large sparse eigenvalue problems was developed at Stanford to address the computational difficulties in the previous methods with the goal to enable accelerator simulations on then the world largest unclassified supercomputer at NERSC for this class of problems. Specifically, a new method, the Hemitian skew-Hemitian splitting method, was proposed and researched as an improved method for solving linear systems with non-Hermitian positive definite and semidefinite matrices.
Date: March 30, 2009
Creator: Golub, Gene & Ko, Kwok
Partner: UNT Libraries Government Documents Department

Optimizing Reinjection Strategy at Palinpinon, Philippines Based on Chloride Data

Description: One of the guidelines established for the safe and efficient management of the Palinpinon Geothermal Field is to adopt a production and well utilization strategy such that the rapid rate and magnitude of reinjection fluid returns leading to premature thermal breakthrough would be minimized. To help achieve this goal, sodium fluorescein and radioactive tracer tests have been conducted to determine the rate and extent of communication between the reinjection and producing sectors of the field. The first objective of this paper is to show how the results of these tests, together with information on field geometry and operating conditions were used in algorithms developed in Operations Research to allocate production and reinjection rates among the different Palinpinon wells. Due to operational and economic constraints, such tracer tests were very limited in number and scope. This prevents obtaining information on the explicit interaction between each reinjection well and the producing wells. Hence, the chloride value of the producing well, was tested to determine if use of this parameter would enable identifying fast reinjection paths among different production/reinjection well pairs. The second aim, therefore, of this paper is to show the different methods of using the chloride data of the producing wells and the injection flow rates of the reinjection wells to provide a ranking of the pair of wells and, thereby, optimize the reinjection strategy of the field.
Date: March 24, 1992
Creator: Urbino, Ma. Elena G. & Horne, Roland N.
Partner: UNT Libraries Government Documents Department

Final Technical Report DE-FG02-99ER14933 Inversion of multicomponent seismic data and rock physics interpretation

Description: An important accomplishment was to understand the seismic velocity anisotropy resulting from the combined roles of depositional stratification and stress in unconsolidated sands. The report presents an experimental study of velocity anisotropy in unconsolidated sands at measured compressive stresses up to 40 bars, which correspond to the first hundred meters of the subsurface. Two types of velocity anisotropy are considered, that due to intrinsic textural anisotropy, and that due to stress anisotropy. We found that sand samples display a bi-linear dependence of velocity anisotropy with stress anisotropy. There exists a transition stress beyond which the stress-induced anisotropy outweighs the intrinsic anisotropy for three different sands.
Date: March 15, 2006
Creator: Mavko, G.
Partner: UNT Libraries Government Documents Department

Elucidating Bioreductive Transformations within Physically Complex Media: Impact on the Fate and Transport of Uranium and Chromium

Description: In situ stabilization (inclusive of natural attenuation) of toxic metals and radionuclides is an attractive approach for remediating many contaminated DOE sites. By immobilizing toxic metals and radionuclides in place, the removal of contaminated water to the surface for treatment as well as the associated disposal costs are avoided. To enhance in situ remediaton, microbiological reductive stabilization of contaminant metals has been, and continues to be, actively explored. It is likely that surface and subsurface microbial activity can alter the redox state of toxic metals and radionuclides, either directly or indirectly, so they are rendered immobile. Furthermore, anaerobic bacterial metabolic products will help to buffer pulses of oxidation, typically from fluxes of nitrate or molecular oxygen, and thus may stabilize reduced contaminants from oxidative mobilization. Uranium and chromium are two elements of particular concern within the DOE complex that, owing to their abundance and toxicity, appear well suited for biologically mediated reductive stabilization. Subsurface microbial activity can alter the redox state of toxic metals and radionuclides, rending them immobile. Imparting an important criterion on the probability that contaminants will undergo reductive stabilization, however, is the chemical and physical heterogeneity of the media. Our research first examined microbially induced transformation of iron (hydr)oxide minerals and their impact on contaminant attenuation. We revealed that in intricate cascade of geochemical reactions is induced by microbially produced Fe(II), and that during transformation contaminants such as U(VI) can be incorporated into the structure, and a set of Fe(II) bearing solids capable of reducing Cr(VI) and stabilizing resulting Cr(III). We also note, however, that common subsurface constituents such as phosphate can modify iron oxide transformation pathways and thus impact contaminant sequestration—affecting both Cr and U stabilization. We extended our work to explore factors controlling the sequestration of uranium in the subsurface, with a particular emphasis on ...
Date: March 1, 2009
Creator: Fendorf, Scott; Francis, Chris; Jardine, Phil & Benner, Shawn
Partner: UNT Libraries Government Documents Department

Stanford geothermal program. Final report, July 1990--June 1996

Description: This report discusses the following: (1) improving models of vapor-dominated geothermal fields: the effects of adsorption; (2) adsorption characteristics of rocks from vapor-dominated geothermal reservoir at the Geysers, CA; (3) optimizing reinjection strategy at Palinpinon, Philippines based on chloride data; (4) optimization of water injection into vapor-dominated geothermal reservoirs; and (5) steam-water relative permeability.
Date: March 1, 1998
Partner: UNT Libraries Government Documents Department

Two-Mile Accelerator Project: Quarterly Status Report, 1 October to 30 December 1962

Description: Introduction: This is the third Quarterly Status Report of work under AEC Contract AT(04-3)-400, held by Stanford University. This contract provides for the construction of the Stanford Linear Accelerator Center (SLAC), a laboratory that will have as its chief instrument a two-mile-long linear electron accelerator.
Date: March 1963
Creator: Chu, E. L.; Ballam, J.; Neal, R. B.; Loew, G.; Eldredge, A. & DeStaebler, H.
Partner: UNT Libraries Government Documents Department

Fracture Permeability and in Situ Stress in the Dixie Valley, Nevada, Geothermal Reservoir

Description: We have collected and analyzed fracture and fluid flow data from wells both within and outside the producing geothermal reservoir at Dixie Valley. Data from wellbore imaging and flow tests in wells outside the producing field that are not sufficiently hydraulically connected to the reservoir to be of commercial value provide both the necessary control group of fracture populations and an opportunity to test the concepts proposed in this study on a regional, whole-reservoir scale. Results of our analysis indicate that fracture zones with high measured permeabilities within the producing segment of the fault are parallel to the local trend of the Stillwater fault and are optimally oriented and critically stressed for frictional failure in the overall east-southeast extensional stress regime measured at the site. In contrast, in the non-producing (i.e., relatively impermeable:) well 66-21 the higher ratio of S{sub hmin} to S{sub v} acts to decrease the shear stress available to drive fault slip. Thus, although many of the fractures at this site (like the Stillwater fault itself) are optimally oriented for normal faulting they are not critically stressed for frictional failure. Although some of the fractures observed in the non-producing well 45-14 are critically stressed for frictional failure, the Stillwater fault zone itself is frictionally stable. Thus, the high horizontal differential stress (i.e., S{sub Hmax}-S{sub hmin}) together with the severe misorientation of the Stillwater fault zone for normal faulting at this location appear to dominate the overall potential for fluid flow.
Date: March 8, 1999
Creator: Zoback, M. D.
Partner: UNT Libraries Government Documents Department

Collaborative Research: Hydrogeological-Geophysical Methods for Subsurface Site Characterization

Description: The significance of this project is that it addresses the issue of site characterization: not only is this issue a very significant budget item in the site clean-up effort, but also it is now realized that accurate and reliable site characterization is the key to the success of any cleanup effort. Our research objective is to develop methodologies for inexpensive high resolution imaging of natural heterogeneities and for relating these heterogeneities to the hydrogeologic parameters that control flow and contaminant transport. Our focus is to help establish the scientific basis for applying shallow geophysics to hydrogeological problems, through sediment-rock physics. This includes identifying uncertainties in applying shallow geophysics interpretations to hydrogeological site characterization.
Date: March 1, 2000
Creator: Rubin, Yoram; Morrison, Frank & Rector, Jamie
Partner: UNT Libraries Government Documents Department

HEAVY AND THERMAL OIL RECOVERY PRODUCTION MECHANISMS

Description: This technical progress report describes work performed from July 1 through September, 2003 for the project ''Heavy and Thermal Oil Recovery Production Mechanisms,'' DE-FC26-00BC15311. In this project, a broad spectrum of research is undertaken related to thermal and heavy-oil recovery. The research tools and techniques span from pore-level imaging of multiphase fluid flow to definition of reservoir-scale features through streamline-based history-matching techniques. During this period, work focused on completing project tasks in the area of multiphase flow and rock properties. The area of interest is the production mechanisms of oil from porous media at high temperature. Temperature has a beneficial effect on oil recovery and reduces residual oil saturation. Work continued to delineate how the wettability of reservoir rock shifts from mixed and intermediate wet conditions to more water-wet conditions as temperature increases. One mechanism for the shift toward water-wet conditions is the release of fines coated with oil-wet material from pore walls. New experiments and theory illustrate the role of temperature on fines release.
Date: March 1, 2004
Creator: Kovscek, Anthony R. & Castanier, Louis M.
Partner: UNT Libraries Government Documents Department

HIGH RESOLUTION PREDICTION OF GAS INJECTION PROCESS PERFORMANCE FOR HETEROGENEOUS RESERVOIRS

Description: This report outlines progress in the second quarter of the third year of the DOE project ''High Resolution Prediction of Gas Injection Process Performance for Heterogeneous Reservoirs''. This report presents results of an investigation of the effects of variation in interfacial tension (IFT) on three-phase relative permeability. We report experimental results that demonstrate the effect of low IFT between two of three phases on the three-phase relative permeabilities. In order to create three-phase systems, in which IFT can be controlled systematically, we employed analog liquids composing of hexadecane, n-butanol, isopropanol, and water. Phase composition, phase density and viscosity, and IFT of three-phase system were measured and are reported here. We present three-phase relative permeabilities determined from recovery and pressure drop data using the Johnson-Bossler-Naumann (JBN) method. The phase saturations were obtained from recovery data by the Welge method. The experimental results indicate that the wetting phase relative permeability was not affected by IFT variation whereas the other two-phase relative permeabilities were clearly affected. As IFT decreases the ''oil'' and ''gas'' phases become more mobile at the same phase saturations.
Date: March 31, 2003
Creator: Franklin M. Orr, Jr.
Partner: UNT Libraries Government Documents Department

HIGH RESOLUTION PREDICTION OF GAS INJECTION PROCESS PERFORMANCE FOR HETEROGENEOUS RESERVOIRS

Description: This report outlines progress in the second 3 months of the first year of the DOE project ''High Resolution Prediction of Gas Injection Process Performance for Heterogeneous Reservoirs.'' The development of an automatic technique for analytical solution of one-dimensional gas flow problems with volume change on mixing is described. The aim of this work is to develop a set of ultra-fast compositional simulation tools that can be used to make field-scale predictions of the performance of gas injection processes. To achieve the necessary accuracy, these tools must satisfy the fundamental physics and chemistry of the displacement from the pore to the reservoir scales. Thus this project focuses on four main research areas: (1) determination of the most appropriate methods of mapping multicomponent solutions to streamlines and streamtubes in 3D; (2) development of techniques for automatic generation of analytical solutions for one-dimensional flow along a streamline; (3) experimental investigations to improve the representation of physical mechanisms that govern displacement efficiency along a streamline; and (4) theoretical and experimental investigations to establish the limitations of the streamline/streamtube approach. In this report they briefly review the status of the research effort in each area. They then give a more in depth discussion of their development of techniques for analytic solutions along a streamline including volume change on mixing for arbitrary numbers of components.
Date: March 31, 2001
Creator: Franklin M. Orr, Jr.
Partner: UNT Libraries Government Documents Department

HIGH RESOLUTION PREDICTION OF GAS INJECTION PROCESS PERFORMANCE FOR HETEROGENEOUS RESERVOIRS

Description: This report outlines progress in the second quarter of the second year of the DOE project ''High Resolution Prediction of Gas Injection Process Performance for Heterogeneous Reservoirs''. A three-dimensional streamline simulator, developed at Stanford University, has been modified in order to use analytical one-dimensional dispersion-free solutions to multicomponent gas injection processes. The use of analytical one-dimensional solutions in combination with streamline simulation is demonstrated to speedup compositional simulations of miscible gas injection processes by orders of magnitude compared to a conventional finite difference simulator. Two-dimensional and three-dimensional examples are reported to demonstrate the potential of this technology. Finally, the assumptions of the approach and possible extensions to include the effects of gravity are discussed.
Date: March 31, 2002
Creator: Franklin M. Orr, Jr.
Partner: UNT Libraries Government Documents Department

Mechanisms of pyrite oxidation to non-slagging species. Quarterly report, July 1, 1996--September 30, 1996

Description: The information presented constitutes the report for the period July 1 to September 30, 1996. Characterization of intraparticle mass transport limitations during pyrite oxidation was embarked upon. The effort was intended to confirm that intraparticle transport limitations are negligible. Samples of 20 micron pyrite particles extracted from the flow reactor after oxidation at 1550 K in 1% oxygen level were analyzed. The samples has been extracted after reaction times of 42 ms, 52 ms, 77 ms, and 146 ms. For these samples, the bulk product compositions previously determined by X-ray diffraction analysis consisted of varying proportions of FeS{sub 2}, Fe{sub 1-X}S, FeO, and Fe{sub 3}O{sub 4}. The particles were analyzed to determine if the iron compounds previously identified by bulk X- ray diffraction analysis (XRD) were well mixed within individual particles. The extracted pyrite particles, epoxied and sectioned, were subjected to a variety of analytical techniques using the microprobe (JEOL 733 Superprobe). Secondary electron and backscatter electron imaging was performed. Iron, sulfur, and oxygen elemental X-ray maps were generated. Energy dispersive spectrometry was used for qualitative elemental analysis of selected particles. These particles were subsequently subjected to qualitative elemental analysis by wavelength dispersive spectrometry (WDS) using Fe{sub 2}O{sub 3} and FeS{sub 2} as standards. During WDS analysis, micron-radius hemispherical volumes bisected by sectioning plane were sampled. The microprobe analyses of oxidized pyrite showed that, generally, particles could be modeled as well-stirred, having negligible compositional gradients of the scale of the particle radius. In all four samples of pyrite analyzed, there were particle edge effects. Furthermore, there were finger-like projections of different phases in mixed-phase particles. Nevertheless, compositional gradients were of concern only in the 77 ms samples.
Date: March 1, 1997
Creator: Akan-Etuk, A.E.J. & Mitchell, R.E.
Partner: UNT Libraries Government Documents Department

Char particle fragmentation and its effect on unburned carbon during pulverized coal combustion. Quarterly report, October 1--December 31, 1994

Description: The project is intended to satisfy, in part, PETC`s research efforts to understand the chemical and physical processes that govern coal combustion. The work is pertinent to the char oxidation phase of coal combustion and focuses on how the fragmentation of coal char particles affects overall mass loss rates and how char fragmentation phenomena influence coal conversion efficiency. The knowledge and information obtained will allow the development of engineering models that can be used to predict accurately char particle temperatures and total mass loss rates during pulverized coal combustion. The overall objectives of the project are: (1) to characterize fragmentation events as a function of combustion environment, (2) to characterize fragmentation with respect to particle porosity and mineral loadings, (3) to assess overall mass loss rates with respect to particle fragmentation, and (4) to quantify the impact of fragmentation on unburned carbon in ash. The knowledge obtained during the course of this project will be used to predict accurately the overall mass loss rates of coals based on the mineral content and porosity of their chars. The work will provide a means of assessing reasons for unburned carbon in the ash of coal fired boilers and furnaces.
Date: March 1, 1995
Creator: Mitchell, R.E.
Partner: UNT Libraries Government Documents Department