Pore-scale numerical modeling of petrophysical properties with applications to hydrocarbon-bearing organic shale

textThe main objective of this dissertation is to quantify petrophysical properties of conventional and unconventional reservoirs using a mechanistic approach. Unconventional transport mechanisms are described from the pore to the reservoir scale to examine their effects on macroscopic petrophysical properties in hydrocarbon-bearing organic shale. Petrophysical properties at the pore level are quantified with a new finite-difference method. A geometrical approximation is invoked to describe the interstitial space of grid-based images of porous media. Subsequently, a generalized Laplace equation is derived and solved numerically to calculate fluid pressure and velocity distributions in the interstitial space. The resulting macroscopic permeability values are within 6% of results obtained with the Lattice-Boltzmann method after performing grid refinements. The finite-difference method is on average six times faster than the Lattice-Boltzmann method. In the next step, slip flow and Knudsen diffusion are added to the pore-scale method to take into account unconventional flow mechanisms in hydrocarbon-bearing shale. The effect of these mechanisms is appraised with a pore-scale image of Eagle Ford shale as well as with several grain packs. It is shown that neglecting slip flow in samples with pore-throat sizes in the nanometer range could result in errors as high as 2000% when estimating permeability in unconventional reservoirs. A new fluid percolation model is proposed for hydrocarbon-bearing shale. Electrical conductivity is quantified in the presence of kerogen, clay, hydrocarbon, water, and the Stern-diffuse layer in grain packs as well as in the Eagle Ford shale pore-scale image. The pore-scale model enables a critical study of the [delta]LogR evaluation method commonly used with gas-bearing shale to assess kerogen concentration. A parallel conductor model is introduced based on Archie's equation for water conductivity in pores and a parallel conductive path for the Stern-diffuse layer. Additionally, a non-destructive core analysis method is proposed for estimating input parameters of the parallel conductor model in shale formations. A modified reservoir model of single-phase, compressible fluid is also developed to take into account the following unconventional transport mechanisms: (a) slip flow and Knudsen diffusion enhancement in apparent permeability, (b) Langmuir desorption as a source of gas generation at kerogen surfaces, and (c) the diffusion mechanism in kerogen as a gas supply to adsorbed layers. The model includes an iterative verification method of surface mass balance to ensure real-time desorption-adsorption equilibrium with gas production. Gas desorption from kerogen surfaces and gas diffusion in kerogen are the main mechanisms responsible for higher-than-expected production velocities commonly observed in shale-gas reservoirs. Slip flow and Knudsen diffusion marginally enhance production rates by increasing permeability during production.Petroleum and Geosystems Engineerin

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Trench capacitor and method for producing the same

A method of fabricating a trench capacitor, and a trench capacitor fabricated thereby, are disclosed. The method involves the use of a vacuum impregnation process for a sol-gel film, to facilitate effective deposition of high- permittivity materials within a trench in a semiconductor substrate, to provide a trench capacitor having a high capacitance whilst being efficient in utilisation of semiconductor real estate

Trench capacitor and method for producing the same

A method of fabricating a trench capacitor, and a trench capacitor fabricated thereby, are disclosed. The method involves the use of a vacuum impregnation process for a sol-gel film, to facilitate effective deposition of high-permittivity materials within a trench in a semiconductor substrate, to provide a trench capacitor having a high capacitance whilst being efficient in utilisation of semiconductor real estate

EGF-induced expansion of migratory cells in the rostral migratory stream.

The presence of neural stem cells in the adult brain is currently widely accepted and efforts are made to harness the regenerative potential of these cells. The dentate gyrus of the hippocampal formation, and the subventricular zone (SVZ) of the anterior lateral ventricles, are considered the main loci of adult neurogenesis. The rostral migratory stream (RMS) is the structure funneling SVZ progenitor cells through the forebrain to their final destination in the olfactory bulb. Moreover, extensive proliferation occurs in the RMS. Some evidence suggest the presence of stem cells in the RMS, but these cells are few and possibly of limited differentiation potential. We have recently demonstrated the specific expression of the cytoskeleton linker protein radixin in neuroblasts in the RMS and in oligodendrocyte progenitors throughout the brain. These cell populations are greatly altered after intracerebroventricular infusion of epidermal growth factor (EGF). In the current study we investigate the effect of EGF infusion on the rat RMS. We describe a specific increase of radixin(+)/Olig2(+) cells in the RMS. Negative for NG2 and CNPase, these radixin(+)/Olig2(+) cells are distinct from typical oligodendrocyte progenitors. The expanded Olig2(+) population responds rapidly to EGF and proliferates after only 24 hours along the entire RMS, suggesting local activation by EGF throughout the RMS rather than migration from the SVZ. In addition, the radixin(+)/Olig2(+) progenitors assemble in chains in vivo and migrate in chains in explant cultures, suggesting that they possess migratory properties within the RMS. In summary, these results provide insight into the adaptive capacity of the RMS and point to an additional stem cell source for future brain repair strategies

Hole transport in the organic small molecule material α-NPD : evidence for the presence of correlated disorder

In this paper the hole mobility in the amorphous small molecule material N,N'-bis(1-naphthyl)-N,N'-diphenyl-1,1'-biphenyl-4,4'-diamine (a-NPD), which is frequently used in organic light-emitting diodes, is studied. From an analysis of the temperature and layer thickness dependence of the steady-state current density in sandwich-type a-NPD-based hole-only devices, it is found that a conventional mobility model assuming a Poole–Frenkel type field dependence and neglecting the carrier density dependence is not appropriate. Consistent descriptions with equal quality are obtained within the framework of two forms of the Gaussian disorder model (GDM and CDM), within which the presence of energetic disorder is described by a Gaussian density of states and within which spatial correlations between the site energies are absent or are included, respectively. Both models contain a carrier density dependence of the mobility. Based on a comparison of the site densities as obtained from both models with the molecular density, we argue that the analysis provides evidence for the presence of correlated disorder

KCl suppresses drug sensitivity in <i>S</i>. <i>pombe</i>

<p><b>A.</b> Wild type (wt) <i>S</i>. <i>pombe</i> cells were cultured in the presence of the 5 μg/ ml bleomycin alone or with indicated concentrations of KCl in the media for 24 h at 30°C. Equal cell numbers were serially diluted and plated on YES agar. Plates were incubated at 30°C for 2–3 days. <b>B.</b> Wt and <i>rad3</i>Δ mutants were exposed to 40 μg/ ml doxorubicin alone or with the indicated concentrations of KCl in the media for 24 h at 30°C and treated as in A. <b>C.</b> Wt and <i>rad3</i>Δ cells were treated as in B, except that the cells were exposed to 10 μg/ ml phleomycin. <b>D.</b> Wt <i>S</i>. <i>pombe</i> cells were incubated with 10 μg/ ml phleomycin alone or with the indicated concentrations of KCl in the media. Cells were fixed in 70% ethanol and examined by microscopy. <b>E.</b> A strain expressing HA- tagged Chk1 was incubated with 10 μg/ ml phleomycin in the presence of the indicated KCl concentrations. Total lysates were resolved by SDS- PAGE and probed with antibodies directed against HA. Tubulin was used to monitor equal gel loading. <b>F.</b> Wt cells were exposed to 100 μg/ ml of G418 or hygromycin for 24 h with or without 0.6 M KCl and then treated as in A. <b>G- P.</b> Wt cells were exposed to the indicated drugs with or without 0.6 M KCl for 24 h and treated as in A.</p

Suppression of Sensitivity to Drugs and Antibiotics by High External Cation Concentrations in Fission Yeast

<div><p>Background</p><p>Potassium ion homeostasis plays an important role in regulating membrane potential and therefore resistance to cations, antibiotics and chemotherapeutic agents in <i>Schizosaccharomyces pombe</i> and other yeasts. However, the precise relationship between drug resistance in <i>S</i>. <i>pombe</i> and external potassium concentrations (particularly in its natural habitats) remains unclear. <i>S</i>. <i>pombe</i> can tolerate a wide range of external potassium concentrations which in turn affect plasma membrane polarization. We thus hypothesized that high external potassium concentrations suppress the sensitivity of this yeast to various drugs.</p><p>Methods</p><p>We have investigated the effect of external KCl concentrations on the sensitivity of <i>S</i>. <i>pombe</i> cells to a wide range of antibiotics, antimicrobial agents and chemotherapeutic drugs. We employed survival assays, immunoblotting and microscopy for these studies.</p><p>Results</p><p>We demonstrate that KCl, and to a lesser extent NaCl and RbCl can suppress the sensitivity of <i>S</i>. <i>pombe</i> to a wide range of antibiotics. Ammonium chloride and potassium hydrogen sulphate also suppressed drug sensitivity. This effect appears to depend in part on changes to membrane polarization and membrane transport proteins. Interestingly, we have found little relationship between the suppressive effect of KCl on sensitivity and the structure, polarity or solubility of the various compounds investigated.</p><p>Conclusions</p><p>High concentrations of external potassium and other cations suppress sensitivity to a wide range of drugs in <i>S</i>. <i>pombe</i>. Potassium-rich environments may thus provide <i>S</i>. <i>pombe</i> a competitive advantage in nature. Modulating potassium ion homeostasis may sensitize pathogenic fungi to antifungal agents.</p></div