Estudo paramétrico da injeção de polímeros em reservatórios de petróleo

Developing an efficient methodology for oil recovery is extremely important . Within the range of enh anced oil recovery, known as EOR, the injection of polymer solutions becomes effective in controlling the mobility of displacing fluid . This method consists of adding polymers to the injection water to increase its viscosity, so that more water diffuses in to the porous medium and increasing the sweep efficiency in the reservoir. This work is studied by numerical simulation , application of the injection polymer solution in a homogeneous reservoir , semisynthetic with similar characteristics to the reservoirs of the Brazilian Northeast , numerical simulations were performed using thermal simulator STARS from CMG (Computer Modelling Group ). The study aimed to analyze the influence of some parameters on the behavior of reservoir oil production, with the response to cumulative production. Simulations were performed to analyze the influence of water injection, polymer solution and alternating injection of water banks and polymer solution, comparing the results for each simulated condition. The primary outcomes were: oil viscosity, percentage of injected polymer, polymer viscosity and flow rate of water injection. The evaluation of the influence of variables consisted of a complete experimental design followed a Pareto analysis for the purpose of pointing out which va riables would be most influential on the response represented b y the cumulative oil production . It was found that all variables significantly influenced the recovery of oil and the injection of polymer solution on an ongoing basis is more efficient for the cumulative production compared to oil recovery by continuous water injection. The primary recovery show ed low levels of oil production , water injection significantly improves the pro duction of oil in the reservoir , but the injection of polymer solution em erges as a new methodology to increase the production of oil, increasing the life of the well and possible reduction of water produced.

Estabilização de órbitas periódicas instáveis utilizando controle por modos deslizantes com compensação adaptativa

The chaotic behavior has been widely observed in nature, from physical and chemical phenomena to biological systems, present in many engineering applications and found in both simple mechanical oscillators and advanced communication systems. With regard to mechanical systems, the effects of nonlinearities on the dynamic behavior of the system are often of undesirable character, which has motivated the development of compensation strategies. However, it has been recently found that there are situations in which the richness of nonlinear dynamics becomes attractive. Due to their parametric sensitivity, chaotic systems can suffer considerable changes by small variations on the value of their parameters, which is extremely favorable when we want to give greater flexibility to the controlled system. Hence, we analyze in this work the parametric sensitivity of Duffing oscillator, in particular its unstable periodic orbits and Poincar´e section due to changes in nominal value of the parameter that multiplies the cubic term. Since the amount of energy needed to stabilize Unstable Periodic Orbits is minimum, we analyze the control action needed to control and stabilize such orbits which belong to different versions of the Duffing oscillator. For that we will use a smoothed sliding mode controller with an adaptive compensation term based on Fourier series.

Caracterização do ritmo circadiano de atividade e repouso em saguis idosos (Callithrix Jacchus)

Advanced age may become a limiting factor for the maintenance of rhythms in organisms, reducing the capacity of generation and synchronization of biological rhythms. In this study, the influence of aging on the expression of endogenous periodicity and synchronization (photic and social) of the circadian activity rhythm (CAR) was evaluated in a diurnal primate, the marmoset (Callithrix jacchus). This study had two approaches: one with longitudinal design, performed with a male marmoset in two different phases: adult (three years) and older (9 y.o.) (study 1) and the second, a transversal approach, with 6 old (♂: 9.7 ± 2.0 y.o.) and 11 adults animals (♂: 4.2 ± 0.8 y.o.) (study 2). The evaluation of the photic synchronization involved two conditions in LD (natural and artificial illuminations). In study 1, the animal was subjected to the following stages: LD (12:12 ~ 350: ~ 2 lx), LL (~ 350 lx) and LD resynchronization. In the second study, the animals were initially evaluated in natural LD, and then the same sequence stages of study 1. During the LL stage in study 2, the vocalizations of conspecifics kept in natural LD on the outside of the colony were considered temporal cue to the social synchronization. The record of the activity was performed automatically at intervals of five minutes through infrared sensor and actimeters, in studies 1 and 2, respectively. In general, the aged showed a more fragmented activity pattern (> IV < H and > PSD, ANOVA, p < 0.05), lower levels of activity (ANOVA, p < 0.05) and shorter duration of active phase (ANOVA, p < 0.05) in LD conditions, when compared to adults. In natural LD, the aged presented phase delay pronounced for onset and offset of active phase (ANOVA, p < 0.05), while the adults had the active phase more adjusted to light phase. Under artificial LD, there was phase advance and greater adjustment of onset and offset of activity in relation to the LD in the aged (ANOVA, p < 0.05). In LL, there was a positive correlation between age and the endogenous period () in the first 20 days (Spearman correlation, p < 0.05), with prolonged  held in two aged animals. In this condition, most adults showed free-running period of the circadian activity rhythm with  < 24 h for the first 30 days and later on relative coordination mediated by auditory cues. In study 2, the cross-correlation analysis between the activity profiles of the animals in LL with control animals kept under natural LD, found that there was less social synchronization in the aged. With the resubmission to the LD, the resynchronization rate was slower in the aged (t-test; p < 0.05) and in just one aged animal there was a loss of resynchronization capability. According to the data set, it is suggested that the aging in marmosets may be related to: 1) lower amplitude and greater fragmentation of the activity, accompanied to phase delay with extension of period, caused by changes in a photic input, in the generation and behavioral expression of the CAR; 2) lower capacity of the circadian activity rhythm to photic synchronization, that can become more robust in artificial lighting conditions, possibly due to the higher light intensities at the beginning of the active phase due to the abrupt transitions between the light and dark phases; and 3) smaller capacity of non-photic synchronization for auditory cues from conspecifics, possibly due to reducing sensory inputs and responsiveness of the circadian oscillators to auditory cues, what can make the aged marmoset most vulnerable, as these social cues may act as an important supporting factor for the photic synchronization.

Caracterização do ritmo circadiano de atividade e repouso em saguis idosos (Callithrix Jacchus)

Advanced age may become a limiting factor for the maintenance of rhythms in organisms, reducing the capacity of generation and synchronization of biological rhythms. In this study, the influence of aging on the expression of endogenous periodicity and synchronization (photic and social) of the circadian activity rhythm (CAR) was evaluated in a diurnal primate, the marmoset (Callithrix jacchus). This study had two approaches: one with longitudinal design, performed with a male marmoset in two different phases: adult (three years) and older (9 y.o.) (study 1) and the second, a transversal approach, with 6 old (♂: 9.7 ± 2.0 y.o.) and 11 adults animals (♂: 4.2 ± 0.8 y.o.) (study 2). The evaluation of the photic synchronization involved two conditions in LD (natural and artificial illuminations). In study 1, the animal was subjected to the following stages: LD (12:12 ~ 350: ~ 2 lx), LL (~ 350 lx) and LD resynchronization. In the second study, the animals were initially evaluated in natural LD, and then the same sequence stages of study 1. During the LL stage in study 2, the vocalizations of conspecifics kept in natural LD on the outside of the colony were considered temporal cue to the social synchronization. The record of the activity was performed automatically at intervals of five minutes through infrared sensor and actimeters, in studies 1 and 2, respectively. In general, the aged showed a more fragmented activity pattern (> IV < H and > PSD, ANOVA, p < 0.05), lower levels of activity (ANOVA, p < 0.05) and shorter duration of active phase (ANOVA, p < 0.05) in LD conditions, when compared to adults. In natural LD, the aged presented phase delay pronounced for onset and offset of active phase (ANOVA, p < 0.05), while the adults had the active phase more adjusted to light phase. Under artificial LD, there was phase advance and greater adjustment of onset and offset of activity in relation to the LD in the aged (ANOVA, p < 0.05). In LL, there was a positive correlation between age and the endogenous period () in the first 20 days (Spearman correlation, p < 0.05), with prolonged  held in two aged animals. In this condition, most adults showed free-running period of the circadian activity rhythm with  < 24 h for the first 30 days and later on relative coordination mediated by auditory cues. In study 2, the cross-correlation analysis between the activity profiles of the animals in LL with control animals kept under natural LD, found that there was less social synchronization in the aged. With the resubmission to the LD, the resynchronization rate was slower in the aged (t-test; p < 0.05) and in just one aged animal there was a loss of resynchronization capability. According to the data set, it is suggested that the aging in marmosets may be related to: 1) lower amplitude and greater fragmentation of the activity, accompanied to phase delay with extension of period, caused by changes in a photic input, in the generation and behavioral expression of the CAR; 2) lower capacity of the circadian activity rhythm to photic synchronization, that can become more robust in artificial lighting conditions, possibly due to the higher light intensities at the beginning of the active phase due to the abrupt transitions between the light and dark phases; and 3) smaller capacity of non-photic synchronization for auditory cues from conspecifics, possibly due to reducing sensory inputs and responsiveness of the circadian oscillators to auditory cues, what can make the aged marmoset most vulnerable, as these social cues may act as an important supporting factor for the photic synchronization.

An application of evolutionary algorithms for WAG optimisation in the Norne Field

Water-alternating-gas (WAG) is an enhanced oil recovery method combining the improved macroscopic sweep of water flooding with the improved microscopic displacement of gas injection. The optimal design of the WAG parameters is usually based on numerical reservoir simulation via trial and error, limited by the reservoir engineer’s availability. Employing optimisation techniques can guide the simulation runs and reduce the number of function evaluations. In this study, robust evolutionary algorithms are utilized to optimise hydrocarbon WAG performance in the E-segment of the Norne field. The first objective function is selected to be the net present value (NPV) and two global semi-random search strategies, a genetic algorithm (GA) and particle swarm optimisation (PSO) are tested on different case studies with different numbers of controlling variables which are sampled from the set of water and gas injection rates, bottom-hole pressures of the oil production wells, cycle ratio, cycle time, the composition of the injected hydrocarbon gas (miscible/immiscible WAG) and the total WAG period. In progressive experiments, the number of decision-making variables is increased, increasing the problem complexity while potentially improving the efficacy of the WAG process. The second objective function is selected to be the incremental recovery factor (IRF) within a fixed total WAG simulation time and it is optimised using the same optimisation algorithms. The results from the two optimisation techniques are analyzed and their performance, convergence speed and the quality of the optimal solutions found by the algorithms in multiple trials are compared for each experiment. The distinctions between the optimal WAG parameters resulting from NPV and oil recovery optimisation are also examined. This is the first known work optimising over this complete set of WAG variables. The first use of PSO to optimise a WAG project at the field scale is also illustrated. Compared to the reference cases, the best overall values of the objective functions found by GA and PSO were 13.8% and 14.2% higher, respectively, if NPV is optimised over all the above variables, and 14.2% and 16.2% higher, respectively, if IRF is optimised.

Sub-wavelength resonators as seismic Rayleigh waves shield

We explore the thesis that tall structures can be protected by means of seismic metamaterials. Seismic metamaterials can be built as some elements are created over soil layer with different shapes, dimensions, patterns and from different materials. Resonances in these elements are acting as locally resonant metamaterials for Rayleigh surface waves in the geophysics context. Analytically we proved that if we put infinite chain of SDOF resonator over the soil layer as an elastic, homogeneous and isotropic material, vertical component of Rayleigh wave, longitudinal resonance of oscillators will couple with each other, they would create a Rayleigh bandgap frequency, and wave will experience attenuation before it reaches the structure. As it is impossible to use infinite chain of resonators over soil layer, we considered finite number of resonators throughout our simulations. Analytical work is interpreted using finite element simulations that demonstrates the observed attenuation is due to bandgaps when oscillators are arranged at sub-wavelength scale with respect to the incident Rayleigh wave. For wavelength less than 5 meters, the resulting bandgaps are remarkably large and strongly attenuating when impedance of oscillators matches impedance of soil. Since longitudinal resonance of SDOF resonator are proportional to its length inversely, a formed array of resonators that attenuates Rayleigh waves at frequency ≤10 Hz could be designed starting from vertical pillars coupled to the ground. Optimum number of vertical pillars and their interval spacing called effective area of resonators are investigated. For 10 pillars with effective area of 1 meter and resonance frequency of 4.9 Hz, bandgap frequency causes attenuation and a sinusoidal impulsive force illustrate wave steering down phenomena. Simulation results proved analytical findings of this work.

Coupled transport in rotor models

Acknowledgement One of us (AP) wishes to acknowledge S. Flach for enlightening discussions about the relationship between the DNLS equation and the rotor model.

A minimal model of partial synchrony

We wish to acknowledge A Pikovsky and M Zaks for useful discussions. This work has been financially supported by the EU project COSMOS (642563).

Generation of harmonic oscillations in ring resonator with high Q-factor

We report on generation of harmonic oscillations with frequencies of hundreds of MHz and radio-frequency linewidth of 13 Hz in unidirectional ring laser oscillator. This high stability makes these oscillators a suitable substitute for existing quartz resonators used in high frequency optoelectronics applications.

An investigation by AFM and TEM of the mechanism of anodic formation of nanoporosity in n-InP in KOH

The early stages of nanoporous layer formation, under anodic conditions in the absence of light, were investigated for n-type InP with a carrier concentration of ∼3× 1018 cm-3 in 5 mol dm-3 KOH and a mechanism for the process is proposed. At potentials less than ∼0.35 V, spectroscopic ellipsometry and transmission electron microscopy (TEM) showed a thin oxide film on the surface. Atomic force microscopy (AFM) of electrode surfaces showed no pitting below ∼0.35 V but clearly showed etch pit formation in the range 0.4-0.53 V. The density of surface pits increased with time in both linear potential sweep and constant potential reaching a constant value at a time corresponding approximately to the current peak in linear sweep voltammograms and current-time curves at constant potential. TEM clearly showed individual nanoporous domains separated from the surface by a dense ∼40 nm InP layer. It is concluded that each domain develops as a result of directionally preferential pore propagation from an individual surface pit which forms a channel through this near-surface layer. As they grow larger, domains meet, and the merging of multiple domains eventually leads to a continuous nanoporous sub-surface region.

Anodic formation and characterization of nanoporous InP in aqueous KOH electrolytes

The anodic behavior of highly doped (> 1018 cm-3) n-InP in aqueous KOH was investigated. Electrodes anodized in the absence of light in 2- 5 mol dm-3 KOH at a constant potential of 0.5- 0.75 V (SCE), or subjected to linear potential sweeps to potentials in this range, were shown to exhibit the formation of a nanoporous subsurface region. Both linear sweep voltammograms and current-time curves at constant potential showed a characteristic anodic peak, corresponding to formation of the nanoporous region. No porous region was formed during anodization in 1 mol dm-3 KOH. The nanoporous region was examined using transmission electron microscopy and found to have a thickness of some 1- 3 μm depending on the anodization conditions and to be located beneath a thin (typically ∼40 nm), dense, near-surface layer. The pores varied in width from 25 to 75 nm and both the pore width and porous region thickness were found to decrease with increasing KOH concentration. The porosity was approximately 35%. The porous layer structure is shown to form by the localized penetration of surface pits into the InP, and the dense, near-surface layer is consistent with the effect of electron depletion at the surface of the semiconductor.

Simultaneous observation of current oscillations and porous film growth during anodization of InP

The observation of spontaneous oscillations in current during the anodization of InP in relatively high concentrations of KOH electrolytes is reported. Oscillations were observed under potential sweep and constant potential conditions. Well-defined oscillations are observed during linear potential sweeps of InP in 5 mol dm-3 KOH to potentials above ∼1.7 V (SCE) at scan rates in the range of 50 to 500 mV s-1. The oscillations observed exhibit an asymmetrical current versus potential profile, and the charge per cycle was found to increase linearly with potential. More complex oscillatory behavior was observed under constant potential conditions. Periodic damped oscillations are observed in high concentrations of electrolyte whereas undamped sinusoidal oscillations are observed in relatively lower concentrations. In both cases, the anodization of InP results in porous InP formation, and the current in the oscillatory region corresponds to the cyclical effective area changes due to pitting dissolution of the InP surface with the coincidental growth of a thick porous In2O3 film.

Anodic behavior of InP: film growth, porous structures and current oscillations.

We review our recent work on the anodization of InP in KOH electrolytes. The anodic oxidation processes are shown to be remarkably different in different concentrations of KOH. Anodization in 2 - 5 mol dm-3 KOH electrolytes results in the formation of porous InP layers but, under similar conditions in a 1 mol dm-3 KOH, no porous structure is evident. Rather, the InP electrode is covered with a thin, compact surface film at lower potentials and, at higher potentials, a highly porous surface film is formed which cracks on drying. Anodization of electrodes in 2 - 5 mol dm-3 KOH results in the formation of porous InP under both potential sweep and constant potential conditions. The porosity is estimated at ~65%. A thin layer (~ 30 nm) close to the surface appears to be unmodified. It is observed that this dense, near-surface layer is penetrated by a low density of pores which appear to connected it to the electrolyte. Well-defined oscillations are observed when InP is anodized in both the KOH and (NH4)2S. The charge per cycle remains constant at 0.32 C cm-2 in (NH4)2S but increases linearly with potential in KOH. Although the characteristics of the oscillations in the two systems differ, both show reproducible and well-behaved values of charge per cycle.

Comparison of oscillatory behavior on InP electrodes in KOH solutions

The observation of current oscillations under potential sweep conditions when an n-InP electrode is anodized in a KOH electrolyte is reported and compared to the oscillatory behavior noted during anodization in an (NH4)2S electrolyte. In both cases oscillations are observed above 1.7 V (SCE). The charge per cycle was found to increase linearly with potential for the InP/KOH system but was observed to be independent of potential for the InP/(NH4)2S system. The period of the oscillations in the InP/KOH was found to increase with applied potential. In this case the oscillations are asymmetrical and the rising and falling segments have a different dependence on potential. Although the exact mechanism is not yet know for either system, transmission electron microscopy studies show that in both cases, the electrode is covered by a thick porous film in the oscillatory region.

Effects of alternating current voltage amplitude and oxide capacitance on mid-gap interface state defect density extractions in In0.53Ga 0.47As capacitors

This work looks at the effect on mid-gap interface state defect density estimates for In0.53Ga0.47As semiconductor capacitors when different AC voltage amplitudes are selected for a fixed voltage bias step size (100 mV) during room temperature only electrical characterization. Results are presented for Au/Ni/Al2O3/In0.53Ga0.47As/InP metal–oxide–semiconductor capacitors with (1) n-type and p-type semiconductors, (2) different Al2O3 thicknesses, (3) different In0.53Ga0.47As surface passivation concentrations of ammonium sulphide, and (4) different transfer times to the atomic layer deposition chamber after passivation treatment on the semiconductor surface—thereby demonstrating a cross-section of device characteristics. The authors set out to determine the importance of the AC voltage amplitude selection on the interface state defect density extractions and whether this selection has a combined effect with the oxide capacitance. These capacitors are prototypical of the type of gate oxide material stacks that could form equivalent metal–oxide–semiconductor field-effect transistors beyond the 32 nm technology node. The authors do not attempt to achieve the best scaled equivalent oxide thickness in this work, as our focus is on accurately extracting device properties that will allow the investigation and reduction of interface state defect densities at the high-k/III–V semiconductor interface. The operating voltage for future devices will be reduced, potentially leading to an associated reduction in the AC voltage amplitude, which will force a decrease in the signal-to-noise ratio of electrical responses and could therefore result in less accurate impedance measurements. A concern thus arises regarding the accuracy of the electrical property extractions using such impedance measurements for future devices, particularly in relation to the mid-gap interface state defect density estimated from the conductance method and from the combined high–low frequency capacitance–voltage method. The authors apply a fixed voltage step of 100 mV for all voltage sweep measurements at each AC frequency. Each of these measurements is repeated 15 times for the equidistant AC voltage amplitudes between 10 mV and 150 mV. This provides the desired AC voltage amplitude to step size ratios from 1:10 to 3:2. Our results indicate that, although the selection of the oxide capacitance is important both to the success and accuracy of the extraction method, the mid-gap interface state defect density extractions are not overly sensitive to the AC voltage amplitude employed regardless of what oxide capacitance is used in the extractions, particularly in the range from 50% below the voltage sweep step size to 50% above it. Therefore, the use of larger AC voltage amplitudes in this range to achieve a better signal-to-noise ratio during impedance measurements for future low operating voltage devices will not distort the extracted interface state defect density.