Dynamic Relative Permeability and Simulation of WAG Injection Processes

In this work, we investigate the impact of mobility changes due to flow reversals from co-current to counter-current flow on the displacement performance of water alternating gas (WAG) injection processes. In WAG processes, the injected gas will migrate toward the top of the formation while the injected water will migrate toward the bottom of the formation. The segregation of gas, oil and water phases will result in counter-current flow occurring in the vertical direction in some portions of the reservoir during the displacement process. Previous experimental and theoretical studies of counter-current flow have shown that the relative mobility of each of the phases in a porous medium is considerably less when counter-current flow prevails as compared to co-current flow settings. A reduction of the relative permeability in the vertical direction results in a dynamic anisotropy in phase mobilities. This effect has, to the best of our knowledge, not previously been considered in the modeling and simulation of WAG processes. A new flow model that accounts for flow reversals in the vertical direction has been implemented and tested in a three-phase compositional reservoir simulator. In order to investigate the impact of flow reversals, results from the new flow model are compared to cases where counter-current flow effects on the phase mobilities are ignored. A range of displacement settings, covering relevant slug sizes, have been investigated to gauge the impact of mobility reductions due to flow reversals. Significant differences, in terms of saturation distribution, producing GOR and oil recovery, are observed between the conventional flow model (ignoring mobility reductions due to counter-current flow) and the proposed new model that accounts for reductions in phase mobility during counter-current flow. Accordingly, we recommend that an explicit representation of flow transitions between co-current and counter-current flow (and the related impact on phase mobilities) should be considered to ensure accurate and optimal design of WAG injection processes.     

A Dynamic Two-Phase Pore-Scale Model of Imbibition

We present a dynamic pore-scale network model of imbibition, capable of calculating residual oil saturation for any given capillary number, viscosity ratio, contact angle, and aspect ratio. Our goal is not to predict the outcome of core floods, but rather to perform a sensitivity analysis of the above-mentioned parameters, except from the viscosity ratio. We find that contact angle, aspect ratio, and capillary number all have a significant influence on the competition between piston-like advance, leading to high recovery, and snap-off, causing oil entrapment. Due to significant CPU-time requirements we did not incorporate long-range correlations among pore and throat sizes in our network, but were limited to small-range correlations. Consequently, the gradual suppression of snap-off occurs within one order of magnitude of the capillary number. At capillary numbers around 10⁸ - 10⁷ snap-off has been entirely inhibited, in agreement with results obtained by Blunt (1997) who used a quasi-static model. For higher aspect ratios, the effect of rate and contact angle is more pronounced.     

Classification of certain subgraphs of the 3‐dimensional grid

We prove by “trial‐ and‐error” that up to isometry, there are exactly four different non‐empty cubic induced subgraphs of the 3‐dimensional grid with girth ≥ 10. © 2002 Wiley Periodicals, Inc. J Graph Theory 42: 34–60, 2003     

Sampling and interpolation of entire functions and exponential systems in convex domains

Research supported by the Norwegian Research Council for Science and Humanities (NAVF).     

Protamine neutralisation of low molecular weight heparins and their oligosaccharide components

Protamine sulphate is an effective inhibitor of heparin and is used clinically to neutralise both low molecular weight heparins (LMWH) and unfractionated heparin (UFH). However, protamine sulphate does not fully counter the anti-Xa effect of LMWH, even in excess (>40 μg to 1 IU/ml). To investigate the molecular basis for this observation, the residual potencies in the presence and absence of plasma as well as the molecular weight profiles of commercial LMWH neutralised with increasing amounts of protamine were measured. Materials over 5000 Da are preferentially neutralised by protamine. To further investigate this molecular weight dependence, monodisperse oligosaccharides were prepared from three commercial LMWHs. The specific anti-Xa activity for the fractions increased with molecular weight, and was found to vary between the three preparations for oligosaccharides of the same molecular weight. Our results indicate that protamine sulphate neutralisation is largely dependent on molecular weight, leading to the implication that LMWHs containing a larger proportion of small oligosaccharides will not be as effectively neutralised. Protamine sulphate neutralisation of any given LMWH is also affected by the specific anticoagulant activities of its low molecular weight components, which varies between LMWH products, presumably with the method of manufacture.     

Femtosecond laser excitation of dielectric materials: experiments and modeling of optical properties and ablation depths

Modeling of the interaction between a dielectric material and ultrashort laser pulses provides the temporal evolution of the electronic excitation and the optical properties of the dielectric. Experimentally determined reflectances and ablation depths for sapphire are compared to the calculations. A decrease in reflectance at high fluences is observed experimentally, which demonstrates the necessity of a temperature-dependent electron scattering rate in the model. The comparison thus provides new constraints on the optical parameters of the model.     

First-principles modelling of scanning tunneling microscopy using non-equilibrium Green’s functions

The investigation of electron transport processes in nano-scale architectures plays a crucial role in the development of surface chemistry and nano-technology. Experimentally, an important driving force within this research area has been the concurrent refinements of scanning tunneling microscopy (STM) techniques. The theoretical treatment of the STM operation has traditionally been based on the Bardeen and Tersoff-Hamann methods which take as input the single-particle wave functions and eigenvalues obtained from finite cluster or slabs models of the surface-tip interface. Here, we present a novel STM simulation scheme based on non-equilibrium Green’s functions (NEGF) and Wannier functions which is both accurate and very efficient. The main novelty of the scheme compared to the Bardeen and Tersoff-Hamann approaches is that the coupling to the infinite (macroscopic) electrodes is taken into account. As an illustrating example we apply the NEGF-STM method to the Si(001)-(2×1):H surface with sub-surface P doping and discuss the results in comparison to the Bardeen and Tersoff-Hamann methods.     

Spectral methods for growth curve clustering

Central European Journal of Operations Research - The growth curve clustering problem is analyzed and its connection with the spectral relaxation method is described. For a given set of growth...     

CXCL10 blockade protects mice from cyclophosphamide-induced cystitis

Background  

Alterations in serum CXCR3 ligand levels were examined in interstitial cystitis (IC) patients; similar expression patterns in serum as well as CXCR3, CXCR3 ligands, and cytokines expressed by peripheral and local leukocyte subpopulations were characterized during cyclophosphamide (CYP)-induced acute cystitis in mice.