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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 523 records · Page 29
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

SNL-SAND-IV v. 0.9 (beta)

The code is used to provide an unfolded/adjusted energy-dependent fission reactor neutron spectrum based upon an input trial spectrum and a set of measured activities. This is part of a neutron environment characterization that supports doing testing in a given reactor environment. An iterative perturbation method is used to obtain a "best fit" neutron flux spectrum for a given input set of infinitely dilute foil activities. The calculational procedure consists of the selection of a trial flux spectrum to serve as the initial approximation to the solution, and subsequent iteration to a form acceptable as an appropriate solution. The solution is specified either as time-integrated flux (fluence) for a pulsed environment or as a flux for a steady-state neutron environment.

Griffin, Patrick J.↗
DOE OSTI2014

1 SEISMIC AMPLITUDES AND ATTENUATIONS OF GAS HYDRATEBEARING SEDIMENTS IN FRACTURED AND SAND RESERVOIRS

Seismic amplitude is principally affected by velocities above and below an interface. However, the amplitude presents attenuation on the hydrate bearing sediments. Thus, seismic interpretation relied on amplitude in elastic wave behavior can not completely reveal seismic characteristics of the hydrate bearing sediments, especially if multiple hydrate layers are present. In the paper, we discuss the physical mechanisms of intrinsic and scattering attenuations. Some previous lab measurements and viscoelastic modeling studies show attenuation behaviors on low frequency and synthetic seismic. Two offset wells provide log data of resistivity, porosity, density, and sonic velocities for identifying hydrate layers and, therefore, allow us to investigate the behaviors of attenuations. The intrinsic and scattering attenuations are significantly in strong dissolved or free gas filling fractures/faults. Hydrate filling fractures/faults are expected to have the effects of intrinsic and scattering attenuations, however it is difficult to distinguish them from no-hydrate filling fractures/faults. In no-fracture/fault zone above the BSR, significant amplitude reduction comparing to background indicates possible fracture-filling hydrate or pore-filling hydrate.

attenuation↗
DOE OSTI2019

Soothing Science: Sanding scientific glass

Take the edge off your day with some #SoothingScience. Craftsmen at ORNL’s glass shop use a diamond grinder to smooth and shape glass plates used for scientific research.

42 ENGINEERING↗
DOE OSTI2016

Linking pore-scale and basin-scale effects on diffusive methane transport in hydrate bearing environments through multi-scale reservoir simulations

We explore the gas hydrate-generating capacity of diffusive methane transport induced by solubility gradients due to pore size contrasts in lithologically heterogeneous marine sediments. Through the use of 1D, 2D, and 3D reactive transport simulations, we investigate scale-dependent processes in diffusion-dominated gas hydrate systems. These simulations all track a sand body, or series of sands, surrounded by clays as they are buried through the gas hydrate stability zone. Methane is sourced by microbial methanogenesis in the clays surrounding the sand layers. In 1D, simulations performed in a Lagrangian reference frame demonstrate that gas hydrate in thin sands (3.6 m thick) can occur in high saturations (upward of 70%) at the edges of sand bodies within the upper 400 meters below the seafloor. Diffusion of methane toward the center of the sand layer depends on the concentration gradient within the sand: broader sand pore size distributions with smaller median pore sizes enhance diffusive action toward the sand’s center. Incorporating downhole log- and laboratory-derived sand pore size distributions, gas hydrate saturations in the center of the sand can reach 20% of the hydrate saturations at the sand’s edges. Furthermore, we show that hydrate-free zones exist immediately above and below the sand and are approximately 5 m thick, depending on the sand-clay solubility contrast. A moving reference frame is also adopted in 2D, and the angle of gravity is rotated relative to the grid system to simulate a dipping sand layer. This is important to minimize diffusive edge effects or numerical diffusion that might be associated with a dipping sand in an Eulerian grid system oriented orthogonal to gravity. Two-dimensional simulations demonstrate the tendency for gas hydrate to accumulate downdip in a sand body because of greater methane transport at depth due to larger sand-clay solubility contrasts. In 3D, basin-scale simulations illuminate how convergent sand layers in a multilayered system can compete for diffusion from clays between them, resulting in relatively low hydrate saturations. All simulations suggest that when hydrate present in clays dissociates with burial, the additional dissolved methane is soaked up by nearby sands preserving high hydrate saturations.

Nole, Michael↗
NASA NTRS1999

The Enigmatic Longevity of Granular Materials on Mars: The Case for Geologically Episodic Dune Formation

Martian sand dunes are concentrated in vast sand seas in the circumpolar belt of the planet's northern hemisphere, but they are also pervasive over the whole planet. Their occurrence is to be expected on a super-arid planetary surface subjected to boundary layer drag from a continually active atmosphere. Whilst their occurrence is to be expected, their survival is enigmatic. But the enigma only arises if the martian system is considered similar to Earth's --where sand is moved highly frequently, more or less on a seasonal basis. Experimentally it is readily demonstrated that active sand will soon wear down to small grains and eventually diminish to below the critical sand size required to sustain dune formation. According to conventional wisdom, sand moves at higher speeds on Mars than on Earth, and if it were to move as frequently as it does on Earth, then the dune-forming sand population should have long since disappeared, given the great longevity of the martian aeolian system (Sagan coined the term "kamikaze" grains to express this disappearance). No supply of sand could keep pace with this depletion, especially in light of the fact that Mars does not have very active weathering, nor significant crustal differentiation. On Earth, plate tectonics, magmatic activity, and general crustal differentiation over geological time have produced great concentrations of quartz crystals in the continental crustal masses. Not only are these quartz grains chemically and mechanically resilient, they are about the right size for being transported by either wind or water. Add to this, the geologically recent contribution of glacial grinding, and it is easy to see why there are dune field on Earth. So what are the martian dunes composed of, and how does the material survive the eons of attrition? In addition to experimental demonstrations of sand comminution in laboratory aeolian simulations, the problem can be approached from first principles. Sagan showed that by simple considerations of material strength versus mechanical work applied to the material, comminution to sub-sand size would be inevitable. Another semi-analytical approach might be taken by considering that the archetypal aeolian sand surface texture is an irregularly pitted ("frosted") surface composed of chipping hollows approximately 10 microns in diameter, 5 microns deep. Their volume = about 250 cubic microns, or about 1/25000 of the volume of a 100 micron diameter dune grain. Because a saltating grain always strikes another grain, then two surfaces are impacted. Thus each grain undergoes two impacts for every one saltation leap, when the impact statistics are considered for a closed dune system (it can be calculated that a grain can never undergo <1 impact, and never >2 per saltation leap). Hence, if we conservatively assume that there is damage to a grain each time it bounces, but with the minimum damage of only 2 microscopic craters per impact, then approximately 12,500 impacts are required to completely eliminate the grain. Of course, it would require only a fraction of this amount to reduce the grain to below sand size. A grain will make only several tens of saltation leaps on the stoss side of a dune before becoming buried on the lee slope. The dune then has to move its full length before the grain is exhumed again for abrasion. Even with this hiatus in transport, it is easy to see that terrestrial dunes need resupplying with sand in order to survive. In recent theoretical work it has been shown that martian aeolian transport may be initiated with high-speed grains, but this converts to a lower energy dynamic transport equilibrium in which a reptation population dominates grain transport (on Earth, at least half of the flux is by reptation and creep). On Mars, therefore, average grain speeds may be lower than those on Earth, or at least comparable. This would permit greater longevity for martian sands, but it would not go far enough to solve the survival problem. It may, however, explain why martian dunes are about the same size as terrestrial dunes. If martian saltation leaps were significantly longer than on Earth (as usually assumed), then a dune's lee slope would have to be correspondingly longer in order to trap the sand; this would scale up the whole dune structure. But with shorter trajectories in a reptation population, larger dunes would be unnecessary. Additional information is contained in the original.

Marshall, J.↗
DOE OSTI2017

Gas hydrate reservoirs and gas migration mechanisms in the Terrebonne Basin, Gulf of Mexico

Here, the interactions of microbial methane generation in fine-grained clay-rich sediments, methane migration, and gas hydrate accumulation in coarse-grained, sand-rich sediments are not yet fully understood. The Terrebonne Basin in the northern Gulf of Mexico provides an ideal setting to investigate the migration of methane resulting in the formation of hydrate in thin sand units interbedded with fractured muds. Using 3D seismic and well log data, we have identified several previously unidentified hydrate bearing units in the Terrebonne Basin. Two units are >100 m- thick fine-grained clay-rich units where gas hydrate occurs in near-vertical fractures. In some locations, these fine-grained units lack fracture features, and they contain 1-4-m thick hydrate bearing-sands. In addition, several other thin sand units were identified that contain gas hydrate, including one sand that was intersected by a well at the location of a discontinuous bottom-simulating reflector. Using correlation of well log data to seismic data, we have mapped and described these new units in detail across the extent of the available data, allowing us to determine the variation of seismic amplitudes and investigate the distribution of free gas and/or hydrate. We present several potential source-reservoir scenarios between the thick fractured mud units and thin hydrate bearing sands. We observe that hydrate preferentially forms within thin sand layers rather than fractures when sands are present in larger marine mud units. Based on regional mapping showing the patchy lateral extent of the thin sand layers, we propose that diffusive methane migration or short-migration of microbially generated methane from the marine mud units led to the formation of hydrate in these thin sands, as discontinuous sands would not be conducive to long-range migration of methane from deeper reservoirs.

03 NATURAL GAS↗
DOE OSTI2011

POLICY ANALYSIS OF PRODUCED WATER ISSUES ASSOCIATED WITH IN-SITU THERMAL TECHNOLOGIES

Commercial scale oil shale and oil sands development will require water, the amount of which will depend on the technologies adopted and the scale of development that occurs. Water in oil shale and oil sands country is already in scarce supply, and because of the arid nature of the region and limitations on water consumption imposed by interstate compacts and the Endangered Species Act, the State of Utah normally does not issue new water rights in oil shale or oil sands rich areas. Prospective oil shale and oil sands developers that do not already hold adequate water rights can acquire water rights from willing sellers, but large and secure water supplies may be difficult and expensive to acquire, driving oil shale and oil sands developers to seek alternative sources of supply. Produced water is one such potential source of supply. When oil and gas are developed, operators often encounter ground water that must be removed and disposed of to facilitate hydrocarbon extraction. Water produced through mineral extraction was traditionally poor in quality and treated as a waste product rather than a valuable resource. However, the increase in produced water volume and the often-higher quality water associated with coalbed methane development have drawn attention to potential uses of produced water and its treatment under appropriations law. This growing interest in produced water has led to litigation and statutory changes that must be understood and evaluated if produced water is to be harnessed in the oil shale and oil sands development process. Conversely, if water is generated as a byproduct of oil shale and oil sands production, consideration must be given to how this water will be disposed of or utilized in the shale oil production process. This report explores the role produced water could play in commercial oil shale and oil sands production, explaining the evolving regulatory framework associated with produced water, Utah water law and produced water regulation, and the obstacles that must be overcome in order for produced water to support the nascent oil shale and oil sands industries.

01 COAL, LIGNITE, AND PEAT↗