326,851 research outputs found
The effect of hydrate content on seismic attenuation: A case study for Mallik 2L-38 well data, Mackenzie delta, Canada
No full textObservations of velocities in sediments containing gashydrates show that the strength of sediments increases with hydrate saturation. Hence it is expected that the attenuation of these sediments will decrease with increasing hydrate saturation. However, sonic log measurements in the Mallik 2L-38 well and cross hole tomography measurements in the Mallik field have shown that attenuation increases with hydrate saturation. We studied a range of mechanisms by which increasing hydrate saturation could cause increased attenuation. We found that a difference in permeability between the host sediment and the newly formed hydrate can produce the observed effect. We modelled attenuation in terms of Biot and squirt flow mechanisms in composite media. We have used our model to predict observed attenuations in the Mallik 2L-38 well, Mackenzie Delta, Canada
The microstructure of sediment-hosted hydrates: evidence from effective medium modelling of laboratory and borehole seismic data
No full textMuch of our knowledge of hydrate distribution in the subsurface comes frominterpretations of remote seismic measurements. A key step in such interpretations isan effective medium theory that relates the seismic properties of a given sediment toits hydrate content. A variety of such theories have been developed; these theoriesgenerally give similar results if the same assumptions are made about the extent towhich hydrate contributes to the load-bearing sediment frame. We have furtherdeveloped and modified one such theory, the self-consistentapproximation/differential effective medium approach, to incorporate additionalempirical parameters describing the extent to which both the sediment matrix material(clay or quartz) and the hydrate are load-bearing. We find that a single choice ofthese parameters allows us to match well both P and S wave velocity measurementsfrom both laboratory and in situ datasets, and that the inferred proportion of hydratethat is load-bearing varies approximately linearly with hydrate saturation. Thisproportion appears to decrease with increasing hydrate saturation for gas-richlaboratory environments, but increase with hydrate saturation when hydrate is formedfrom solution and for an in situ example
Scientometric Portrait of Nobel Laureate S. Chandrasekhar
No full textScientometric analysis of the publications productivity of Nobel Laureate S. Chandrasekhar is documented
Seismic constraints on the effects of gas hydrate on sediment physical properties and fluid flow: a review
No full textThe formation of gas hydrates in marine sediments changes their physical properties and hence influences fluid flow. Here, we review seismic indicators of gas hydrates and relate these indicators to gas hydrate formation and fluid migration. Analyses of seismic data from sediments containing gas and gas hydrates in a variety of locations have shown that the characteristic bottom‐simulating reflector (BSR), which commonly marks the hydrate phase boundary is caused mainly by the presence of gas beneath the gas hydrate stability zone (GHSZ). The amplitude of the BSR is also dependent on the hydrate concentration and on the porosity of the sediment. The presence of gas hydrate alters the elastic properties of sediments, particularly if it cements sediment grains. However, multifrequency studies in various geological provinces show that any loss of reflectivity or blanking observed within the GHSZ is dependent on both the nature of the sediments and concentration of hydrate present. Gas beneath the BSR may cause amplitude anomalies and may result in bright spots and enhanced reflections. The presence of gas beneath the BSR is the primary cause of observed amplitude versus offset (AVO) anomalies, but the amplitude of these anomalies is also dependent on the amount of cementation brought by the gas hydrates within the GHSZ.Fluid migration appears to play an important role in the formation and dissociation of gas hydrates in both active and passive margin settings. Fluid migration in accretionary prisms influences hydrate accumulation and may therefore control the spatial distribution of BSRs. Fluid migration may influence also the type of hydrate formed by bringing thermogenic gas containing higher order hydrocarbons to the GHSZ from below. Fluid advection may cause local dissociation of gas hydrates by bringing heat from below, thus shifting the gas hydrate phase boundary. Fluid flow within the GHSZ is limited by the formation of hydrate in the pore space, which reduces the permeability of the sediment. Features such as pockmarks, acoustic masking and acoustic turbidity are indirect indicators of fluid flow and identification of these features in seismic sections within and beneath the GHSZ may also suggest the formation of gas hydrate.<br/
DRS+IRT Minimal Dataset
No full textPatient and measurement data for combined DRS and IRT measurements for cellulitis diagnosis
The Significance of Pressure Injuries and Purpura in COVID-19 Patients Hospitalized at a Large Urban Academic Medical Center: A Retrospective Cohort Study - Supplemental Table
No full textThe Significance of Pressure Injuries and Purpura in COVID-19 Patients Hospitalized at a Large Urban Academic Medical Center: A Retrospective Cohort Study - Supplemental Tabl
Characterization of the Performance of an XXZ Three-Spin Quantum Battery
No full textQuantum batteries represent a new and promising technological application of quantum mechanics, offering the potential for enhanced energy storage and fast charging. In this work, we study a quantum battery composed of three two-level systems with XXZ coupling operating under open boundary conditions. We investigate the role played by ferromagnetic and antiferromagnetic initial configurations on the charging dynamics of the battery. Two charging mechanisms are explored: static charging, where the battery interacts with a constant classical external field, and harmonic charging, where the field oscillates periodically over time. Our results demonstrate that static charging can be more efficient in the ferromagnetic case, achieving maximum energy due to complete population inversion between the ground and excited states. In contrast, harmonic charging excels in the antiferromagnetic case. By analyzing the stored energy and the average charging power in these two regimes, we highlight the impact of anisotropy on the performance of quantum batteries. Our findings provide valuable insights for optimizing quantum battery performance based on the system’s initial state and coupling configuration, paving the way for the study of more efficient quantum devices for energy storage
Suite Des Oeuvres
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