Field Validation of a Non-logging Alternative Method for the Prediction of the Location of Water-Cresting in Horizontal Wells for Water-Drive Reservoirs.

A previously reported method for a non-logging alternative method for the prediction of the location of water-cresting in horizontal wells for water-drive reservoirs is validated in a field test for the first time in this study. Using this method, the wellbore trajectory, variation in the reservoir permeability, and the pressure gradient data were used to calculate what is called the breakthrough coefficient for the different segments along the length of a set horizontal well with the largest calculated breakthrough coefficient corresponding to the most likely location of the actual water-cresting occurrence. This method was field-validated and found to be in good agreement with log testing for a group of seven wells in an oilfield in Northern China. Another calculated parameter derived from the breakthrough coefficient which is called the variation of the breakthrough coefficients that characterize the effect of the variation of water production along the length of the horizontal well due to the effect of the variation of the wellbore trajectory, permeability, and pressure gradient on the oil production is also introduced. This field validation found variation of the breakthrough coefficients to be weakly and inversely correlated to the oil production in application to a group of 27 wells in the same field.

Method of Predicting the Location of Water Cresting for Horizontal Wells in a Water-Drive Reservoir for Early Prevention.

A method of prediction of location of water cresting and characterizing its intensity in a horizontal well in a water-drive reservoir is introduced for the first time. A mechanistic model for water cresting derived from Darcy's equation incorporating the main parameters reported in the literature affecting water cresting-viscosity, well distance to the aquifer, wellbore pressure gradient, and reservoir heterogeneity-is introduced with two new characterizing parameters. First is a model-derived parameter, called the breakthrough coefficient, which is defined as the ratio of the average time of breakthrough to the time of breakthrough for a segment of the well, with the model-predicted location of water cresting corresponding to the well segment with the largest breakthrough coefficient. The second is the Cresting index, which is the ratio of the maximum breakthrough coefficient to the minimum breakthrough coefficient as a characterizing parameter, with a well with a higher cresting index corresponding to a faster breakthrough in a group of similar wells. This methodology was validated through a series of sophisticated experimental corefloods and found to predict 78% of the location of the water cresting accurately. The cresting index is found to be weakly correlated with the speed of breakthrough among similar wells.

Experimental study on factors affecting the end effect in gas viscosity measurement using capillary-tube viscometer.

Because of its simple principle and high adaptability to severe operational conditions, the capillary-tube viscometer has been widely used for viscosity measurement. However, difficulties in accurately correcting the end effect induced measurement deviation will result in great uncertainty for measurement results. In order to solve this problem, in this work, we studied factors affecting the end effect by conducting the high pressure nitrogen viscosity measurement at low flow velocity with an improved capillary-tube viscometer. The experimental results indicated that the influence of the end effect became less significant with the decrease in flow velocity (v) and tube inner diameter (d) and varied inversely with the length of tube (L). We defined the ratio of measured viscosity to standard viscosity obtained from the NIST database as the viscosity deviation coefficient (Ce). From the Ce vs v, Ce vs d, and Ce vs L curves, we have observed that there existed a threshold velocity (vthreshold), a threshold diameter (dthreshold), and a threshold length (Lthreshold) at which Ce got closer to 1.0. It suggested that under certain experimental conditions, the influence of the end effect on gas viscosity measurement became negligible. Based on that, we established end effect free capillary-tube viscometry and compared the nitrogen viscosity results measured by this method with the data provided by the NIST database. The results presented a good match with error within 1.2%. These insights will contribute to improving the accuracy of a capillary-tube viscometer especially under high pressure.

Evaluation of carbon nanotube probes in critical dimension atomic force microscopes.

The decreasing size of semiconductor features and the increasing structural complexity of advanced devices have placed continuously greater demands on manufacturing metrology, arising both from the measurement challenges of smaller feature sizes and the growing requirement to characterize structures in more than just a single critical dimension. For scanning electron microscopy, this has resulted in increasing sophistication of imaging models. For critical dimension atomic force microscopes (CD-AFMs), this has resulted in the need for smaller and more complex tips. Carbon nanotube (CNT) tips have thus been the focus of much interest and effort by a number of researchers. However, there have been significant issues surrounding both the manufacture and use of CNT tips. Specifically, the growth or attachment of CNTs to AFM cantilevers has been a challenge to the fabrication of CNT tips, and the flexibility and resultant bending artifacts have presented challenges to using CNT tips. The Korea Research Institute for Standards and Science (KRISS) has invested considerable effort in the controlled fabrication of CNT tips and is collaborating with the National Institute of Standards and Technology on the application of CNT tips for CD-AFM. Progress by KRISS on the precise control of CNT orientation, length, and end modification, using manipulation and focused ion beam processes, has allowed us to implement ball-capped CNT tips and bent CNT tips for CD-AFM. Using two different generations of CD-AFM instruments, we have evaluated these tip types by imaging a line/space grating and a programmed line edge roughness specimen. We concluded that these CNTs are capable of scanning the profiles of these structures, including re-entrant sidewalls, but there remain important challenges to address. These challenges include tighter control of tip geometry and careful optimization of scan parameters and algorithms for using CNT tips.

Atomically Traceable Nanostructure Fabrication.

Reducing the scale of etched nanostructures below the 10 nm range eventually will require an atomic scale understanding of the entire fabrication process being used in order to maintain exquisite control over both feature size and feature density. Here, we demonstrate a method for tracking atomically resolved and controlled structures from initial template definition through final nanostructure metrology, opening up a pathway for top-down atomic control over nanofabrication. Hydrogen depassivation lithography is the first step of the nanoscale fabrication process followed by selective atomic layer deposition of up to 2.8 nm of titania to make a nanoscale etch mask. Contrast with the background is shown, indicating different mechanisms for growth on the desired patterns and on the H passivated background. The patterns are then transferred into the bulk using reactive ion etching to form 20 nm tall nanostructures with linewidths down to ~6 nm. To illustrate the limitations of this process, arrays of holes and lines are fabricated. The various nanofabrication process steps are performed at disparate locations, so process integration is discussed. Related issues are discussed including using fiducial marks for finding nanostructures on a macroscopic sample and protecting the chemically reactive patterned Si(100)-H surface against degradation due to atmospheric exposure.

Nucleic acid affinity of clustered-charge anion exchange adsorbents: effects of ionic strength and ligand density.

In previous work we demonstrated the improved protein-binding capacity and selectivity of ion-exchange adsorbents displaying a "clustered" rather than random, distribution of surface charges. For example, anion-exchange adsorbents displaying 5 mM of positive charge in the form of 1 mM penta-argininamide show much higher affinity and capacity for alpha-lactalbumin than do adsorbents displaying the same 5 mM total charge in the form of single dispersed argininamide charges. We also found that clustered adsorbents selectively favor proteins with inherent charge clustering. In the present work, "clustered" penta-argininamide adsorbents showed DNA binding capacity comparable to that of conventional dispersed adsorbents with 10-100-fold higher ligand density. We also observed that at moderate ionic strength the DNA affinity of all adsorbents tested increased with salt while RNA affinity decreased, so that selectivity for DNA over RNA was enhanced as salt concentration increased.

A moving window correlation method to reduce the distortion of scanning probe microscope images.

Many scanning probe microscopes such as the scanning tunneling microscope and atomic force microscope use piezoelectric actuators operating in open loop for generating the scans of the surfaces. However, nonlinearities mainly caused by hysteresis and drift of piezoelectric actuators reduce the positioning accuracy and produce distorted images. A moving window correlation method is proposed in this paper to determine and quantify the hysteresis. This method requires both trace and retrace profiles to be recorded. With a window imposed on each of the profiles, correlations are implemented between the data inside two windows to find corresponding pixel pairs on two different profiles but the same physical positions along the fast scanning axis (x). The x-distances between pixel pairs are calculated and then a simple correction scheme is applied to reduce the distortion.

Three-dimensional image correction of tilted samples through coordinate transformation.

In scanned probe measurements of micrometer- or nanometer-scale lines, it is nearly impossible to maintain the sample in a perfectly level position, and even a small amount of tilt can contribute to the accuracy of the result of the measure such as linewidth or step height. The current practice in image processing to deal with this problem is to conduct a line-by-line analysis to find the best fit of the substrate profile and subtract this background from all data points, thus describing 3D plane turns as a series of lines and processing them in succession in the x- or y-direction. In this paper a coordinate transformation method is proposed. The new coordinate system can be established on the basis of the inclined angle of the sample as well as the translation of three axes between the old coordinate system and the new coordinate system. The method can mathematically derive and hence correct all tilts around the x-, y- and z-axes and produce a leveled image simultaneously. Feature dimensions such as width, height, sidewall angle and pitch are calculated on the basis of simulated images using the coordinate transformation method and other methods. The result shows the advantage of the proposed method.

Computational models of a nano probe tip for static behaviors.

It is difficult to predict the measurement bias arising from the compliance of the atomic force microscope (AFM) probe. The issue becomes particularly important in this situation where nanometer uncertainties are sought for measurements with dimensional probes composed of flexible carbon nanotubes mounted on AFM cantilevers. We have developed a finite element model for simulating the mechanical behavior of AFM cantilevers with carbon nanotubes attached. Spring constants of both the nanotube and cantilever in two directions are calculated using the finite element method with known Young's moduli of both silicon and multiwall nanotube as input data. Compliance of the nanotube-attached AFM probe tip may be calculated from the set of spring constants. This paper presents static models that together provide a basis to estimate uncertainties in linewidth measurement using nanotubes. In particular, the interaction between a multiwall nanotube tip and a silicon sample is modeled using the Lennard-Jones theory. Snap-in and snap-out of the probe tip in a scanning mode are calculated by integrating the compliance of the probe and the sample-tip interacting force model. Cantilever and probe tip deflections and points of contact are derived for both horizontal scanning of a plateau and vertically scanning of a wall. The finite element method and the Lennard-Jones model provide a means to analyze the interaction of the probe and sample and measurement uncertainty, including actual deflection and the gap between the probe tip and the measured sample surface.

Enhanced protein affinity and selectivity of clustered-charge anion-exchange adsorbents.

In this work, we examined the possibility of improving ion-exchange adsorbent performance by nanoscale structuring of ligands into clusters of fixed size rather than a random distribution of individual charges. The calcium-depleted form of the protein alpha-lactalbumin, which displays a cluster of acidic amino acid residues, showed enhanced adsorption affinity and capacity on clustered-charge pentalysinamide and pentaargininamide adsorbents as compared to single-charge lysinamide and argininamide adsorbents of matched total charge. Two differently charge-clustered mutants of rat microsomal cytochrome b(5), E11Q and E44Q, with the same total charge also were well differentiated by clustered-charge adsorbents. Thus, an organized rather than random distribution of charges may produce adsorbents with higher capacity and selectivity, especially for biomolecules with inherent charge clustering.

Water-elutability of nucleic acids from metal-chelate affinity adsorbents: enhancement by control of surface charge density.

Immobilized metal affinity chromatography (IMAC) is widely used for purification of proteins, especially "hexahistidine-tagged" recombinant proteins. We previously demonstrated the application of IMAC to selective capture of nucleic acids, including RNA, selectively-denatured genomic DNA, and PCR primers through interactions with purine bases exposed in single-stranded regions. We also found that the binding affinity of nucleic acids for IMAC adsorbents can be increased several-fold by addition of 20 volume% of neutral additives such as ethanol or DMSO. In the present work, it is demonstrated that bound nucleic acids can be effectively eluted with water instead of the usual imidazole-containing competitive eluants, when the surface density of negative charges is enhanced by operation at alkaline pH, or by deliberate metal-underloading of the anionic chelating ligands. With enhanced negative surface charge density, nucleic acid adsorption can be made strongly dependent on the presence of adsorption-promoting additives and/or repulsion-shielding salts, and removal of these induces elution. Complete water-elutability is demonstrated for baker's yeast RNA bound to 10% Cu(II)- underloaded IDA Chelating Sepharose in a binding buffer of 20 mM HEPES, 240 mM NaCl, pH 7. Water elutability will significantly enhance the utility of IMAC in nucleic acid separations.

Neutral additives enhance the metal-chelate affinity adsorption of nucleic acids: role of water activity.

Immobilized metal-chelate affinity chromatography has been widely used in the purification of proteins, and we have recently found that it can also be applied to purification of nucleic acids through interactions involving exposed bases, especially purines. Here we report that the inclusion of moderate quantities of neutral solutes in the buffer substantially enhances the binding affinity of nucleic acids for immobilized metal-chelate affinity adsorbents. Addition of 20% (v/v) of solutes such as ethanol, methanol, isopropanol, n-propanol, and dimethyl sulfoxide enhances the initial affinity of binding of total yeast RNA by 4.4-, 3.8-, 3.7-, 3.0-, and 2.8-fold, respectively for Cu(II)-iminodiacetic acid (IDA) agarose adsorbent, and the weaker adsorption by Cu(II)-nitrilotriacetic acid (NTA) agarose was even more strongly enhanced. The adsorption affinities of the smaller oligodeoxynucleotide molecules A20, G20, C20 and T20 also increase with the addition of ethanol, suggesting that the effect is not significantly mediated by conformational changes. Binding enhancement generally correlates with reduction of water activity by the various solutes, as predicted by several models of solution thermodynamics, consistent with an entropic contribution by displacement of waters from the metal-chelate. Interestingly, the enhancement was not seen with the proteins bovine serum albumin and lysozyme.

The influence of defects on the morphology of Si (111) etched in NH4F.

We have implemented a kinetic Monte Carlo (KMC) simulation to study the effects of wafer miscut and wafer defects on the morphologies of Si (111) surfaces etched in NH4F. Although a conventional KMC simulation reproduced previously published results, it failed to produce the morphologies observed in our experiments. By introducing both dopant sites and lattice defect sites into the model, we are able to simulate samples having different dopant elements and densities as well as different defect concentrations. Using the modified KMC simulation, the simulated surface morphologies agree well with the morphologies observed in our experiments. The enhanced model also gives insights to the formation mechanism for multiple level stacking pits, a notable morphology on the etched surfaces of samples with very small miscut angles.

Discrepancies between roughness measurements obtained with phase-shifting and white-light interferometry.

Discrepancies between phase-shifting and white-light interferometry have been observed in step-height and surface roughness measurements. The discrepancies have a strong relation to the roughness average parameter of the surface. The skewing effect, which mainly occurs in the vicinity of peaks, valleys, and edges of the sample, causes this problem in white-light interferometry of step height. For roughness, two possible sources of the discrepancy are considered.

Certification of NIST SRM 1962: 3 µm Diameter Polystyrene Spheres.

This report describes the certification of SRM 1962, a NIST Standard Reference Material for particle diameter. It consists of an aqueous suspension of monosize 3 (µm polystyrene spheres. Two calibration techniques were used: optical microscopy and electron microscopy. The first one gave a mean diameter of [Formula: see text] µm and a standard deviation of the size distribution σD = 0.020 µm, based on measurement of 4600 spheres. The second technique gave [Formula: see text] µm, based on measurement of 120 spheres. The reported value covering the two results is [Formula: see text] µm with a maximum uncertainly of 0.016 µm, with σD =0.020 µm.