Constant Composition Research Articles

Clay mineralogy of the Stari Slankamen (Serbia) loess-paleosol sequence during the last glacial cycle — Implications for dust provenance and interglacial climate

Clay minerals in loess-paleosol sequences carry important information on dust source and the paleoenvironments of the areas of loess distribution. The loess-paleosol sequences in the Serbian part of the Carpathian Basin are among the most complete Quaternary terrestrial sedimentary sequences in Europe. However, relatively little is known about the origin and temporal variations of clay minerals in these deposits and their paleoclimatic implications. Here we present the results of high-resolution XRD clay mineral analysis of the Stari Slankamen loess-paleosol sequence through the last glacial cycle. The roughly constant composition of the clay minerals within the loess unit and most of the paleosol suggests that the clay minerals are of detrital origin and that pedogenic transformation has only occurred in the lower part of paleosol S1, which corresponds to the climatic optimum of Marine Isotope Stage (MIS) 5e. This provides a basis for addressing several important issues regarding the Carpathian Basin loess, including its provenance, glacial dust activity, and the interglacial climate. The smectite-rich characteristic of the glacial loess provides a diagnostic indicator for confirming local sources for the Carpathian Basin loess deposits, and that these sources made little contribution to the dust deposited in Greenland during the last glacial. The first application of illite crystallinity and the chlorite ratio to the Carpathian Basin loess-paleosol sequence suggests that they are more sensitive indicators than the clay mineral proxies previously used in European loess studies. The enhanced precipitation during MIS 5e indicated by the new proxies and the transformation of clay mineral potentially provide new insights into understanding the regional climatic response to future global warming.

Optimization of the parameters of a laser induced breakdown spectrometer (LIBS) using probabilistic-deterministic design of experiment

A method for optimizing the settings of a LIBS device aimed at achieving the maximum intensity of analytical lines of the analyte of constant composition is considered using probabilistic-deterministic design of experiments (PDDE). A mixture of Cr, Mn, Fe, Co, and Ni oxides homogenized and diluted by fusion with a lead-phosphate mixture is used as an analyte. It is shown that data of mathematical processing of 25 spectra by the PDDE method can be used to develop mathematical models which relate the line intensity with the energy of the laser pumping lamp, the lag time of the first and second Q-switches, the time delay of the exposure onset, and the total exposure time. The use of the geometric mean and mathematical model in the form of the product of the partial dependences leads to a good correlation between the calculated and experimental values of the intensity for all the considered spectral lines. The simulation results presented for 16 analytical lines of Cr, Mn, Co, and Ni illustrate the applicability of the method under consideration. The experimentally achieved maximum intensities of analytical lines in the matrix of lead-phosphate glass differ from those calculated using the obtained models by 7 – 12 %. There is a linear correlation between the experimental and calculated values of the intensity at R2 = 0.99 and an inclination angle close to 45°. The spectra recorded during the experiment can be used for optimization of other parameters, e.g., the signal-to-noise ratio. The simplicity of calculations and relatively small number of tests in the optimization experiment make the PDDE a promising method for optimizing the LIBS parameters.

Grain size effects on activation energy and conductivity: Na-[formula omitted]″-alumina ceramics and ion conductors with highly resistive grain boundary phases

As for many ion conductors, the electrical conductivity of polycrystalline Na-β″-alumina reported in literature varies by over two decades at a given temperature. This is often ascribed to a combination of variable effects related to grain size, composition, phase content, porosity and impurities, but the dominating factors are rarely identified. Based on an extensive set of Li2O-stabilized Na-β”-alumina ceramics sintered at different conditions, we evaluate a sample series with constant composition and phase content but variable conductivity. The total conductivity of the polycrystalline samples features pronounced non-Arrhenius temperature dependence. To explain this effect, we present a simple microstructural model describing the influence of grain size effects in Arrhenius-type ion conductors with highly resistive grain boundaries as a second phase. We show that this model further predicts a linear relationship between conductivity and effective activation energy at a given temperature, which we also observe experimentally. Based on this, we are able to identify to which extent conductivity variations in a given data set may be explained by grain size effects only. As the same microstructural model relates fundamental transport properties of the corresponding grain and grain boundary phases with the experimentally observed linear relationship, we further discuss how these parameters can be extracted, e.g. by taking into account experimentally determined grain size data. Comparison with literature data indicates for which Na-β″-alumina samples additional effects such as changes in composition and percolation of coarse grains are relevant for the transport properties. Our findings on the relation between effective conductivity and corresponding activation energy are applicable to Arrhenius-type ion conductors with highly resistive grain boundary phases in general.

Molecular Weight Dependence of Block Copolymer Micelle Fragmentation Kinetics.

The effect of molecular weight (M) on the fragmentation kinetics of micelles formed by 1,2-polybutadiene-block-poly(ethylene oxide) (PB-PEO) copolymers was studied in the ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide. A series of six samples, with total M ranging from 104 to 105 g mol-1 and nearly constant composition (fPEO ≈ 0.4), were examined; all six formed spherical micelles with PEO coronas. Nonequilibrium PB-PEO micelles were prepared by direct dissolution, a process that systematically produces nanoparticles with mean aggregation numbers more than twice the equilibrium values. When subjected to high temperature annealing (170 °C), the average micelle radius was found to decrease substantially, as determined by temperature-jump dynamic light scattering (T-jump DLS) and time-resolved small-angle X-ray scattering (TR-SAXS). The characteristic fragmentation times (τ) were found to increase strongly with increasing degree of polymerization N, as τ ∼ N1.8. This result compares favorably with the prediction of a previously untested model.

Stratospheric carbon isotope fractionation and tropospheric histories of CFC-11, CFC-12, and CFC-113 isotopologues

Abstract. We present novel measurements of the carbon isotope composition of CFC-11 (CCl3F), CFC-12 (CCl2F2), and CFC-113 (CF2ClCFCl2), three atmospheric trace gases that are important for both stratospheric ozone depletion and global warming. These measurements were carried out on air samples collected in the stratosphere – the main sink region for these gases – and on air extracted from deep polar firn snow. We quantify, for the first time, the apparent isotopic fractionation, ϵapp(13C), for these gases as they are destroyed in the high- and mid-latitude stratosphere: ϵapp(CFC-12, high-latitude) =(-20.2±4.4) ‰, and ϵapp(CFC-113, high-latitude) =(-9.4±4.4) ‰, ϵapp(CFC-12, mid-latitude) =(-30.3±10.7) ‰, and ϵapp(CFC-113, mid-latitude) =(-34.4±9.8) ‰. Our CFC-11 measurements were not sufficient to calculate ϵapp(CFC-11), so we instead used previously reported photolytic fractionation for CFC-11 and CFC-12 to scale our ϵapp(CFC-12), resulting in ϵapp(CFC-11, high-latitude) =(-7.8±1.7) ‰ and ϵapp(CFC-11, mid-latitude) =(-11.7±4.2) ‰. Measurements of firn air were used to construct histories of the tropospheric isotopic composition, δT(13C), for CFC-11 (1950s to 2009), CFC-12 (1950s to 2009), and CFC-113 (1970s to 2009), with δT(13C) increasing for each gas. We used ϵapp(high-latitude), which was derived from more data, and a constant isotopic composition of emissions, δE(13C), to model δT(13C, CFC-11), δT(13C, CFC-12), and δT(13C, CFC-113). For CFC-11 and CFC-12, modelled δT(13C) was consistent with measured δT(13C) for the entire period covered by the measurements, suggesting that no dramatic change in δE(13C, CFC-11) or δE(13C, CFC-12) has occurred since the 1950s. For CFC-113, our modelled δT(13C, CFC-113) did not agree with our measurements earlier than 1980. This discrepancy may be indicative of a change in δE(13C, CFC-113). However, this conclusion is based largely on a single sample and only just significant outside the 95 % confidence interval. Therefore more work is needed to independently verify this temporal trend in the global tropospheric 13C isotopic composition of CFC-113. Our modelling predicts increasing δT(13C, CFC-11), δT(13C, CFC-12), and δT(13C, CFC-113) into the future. We investigated the effect of recently reported new CFC-11 emissions on background δT(13C, CFC-11) by fixing model emissions after 2012 and comparing δT(13C, CFC-11) in this scenario to the model base case. The difference in δT(13C, CFC-11) between these scenarios was 1.4 ‰ in 2050. This difference is smaller than our model uncertainty envelope and would therefore require improved modelling and measurement precision as well as better quantified isotopic source compositions to detect.

Multi-Class Cost-Constrained Random Coding for Correlated Sources over the Multiple-Access Channel.

This paper studies a generalized version of multi-class cost-constrained random-coding ensemble with multiple auxiliary costs for the transmission of N correlated sources over an N-user multiple-access channel. For each user, the set of messages is partitioned into classes and codebooks are generated according to a distribution depending on the class index of the source message and under the constraint that the codewords satisfy a set of cost functions. Proper choices of the cost functions recover different coding schemes including message-dependent and message-independent versions of independent and identically distributed, independent conditionally distributed, constant-composition and conditional constant composition ensembles. The transmissibility region of the scheme is related to the Cover-El Gamal-Salehi region. A related family of correlated-source Gallager source exponent functions is also studied. The achievable exponents are compared for correlated and independent sources, both numerically and analytically.

Laboratory Investigation of Permeability Impairment Caused by Asphaltene Precipitation during Screening for Gas-Injection Enhanced Oil Recovery and Pressure Change in a Major Gulf of Mexico Field

Summary As part of studying miscible gas injection (GI) in a major field within the Green Canyon protraction area in the Gulf of Mexico (GOM), asphaltene-formation risk was identified as a key factor affecting a potential GI project. The industry has not conducted many experiments to quantify the effect of asphaltenes on reservoir and well performance under GI conditions. In this paper we discuss a novel laboratory test for evaluating the asphaltene effect on permeability. The goals of the study were to define the asphaltene-precipitation envelope using blends of reservoir fluid and injection gas, and measure permeability reduction caused by asphaltene precipitation in a core under GI. To properly analyze the effect of GI, a suite of fluid-characterization studies was conducted, including restored-oil samples, compositional analysis, constant composition expansion (CCE), and differential vaporization. Miscibility conditions were defined through slimtube-displacement tests. Gas solubility was determined through swelling tests complemented by asphaltene-onset-pressure (AOP) testing. The unique procedure was developed to estimate the effect of asphaltene deposition on core permeability. The 1-ft-long core was saturated with the live-oil and GI mixture at a pressure greater than the AOP, and then pressure was depleted to a pressure slightly greater than the bubblepoint. Several cycles of charging and depletion were conducted to mimic continuous flow of oil along the path of injected gas and thereby to observe the accumulation of asphaltene on the rock surface. The test results indicated that during this cyclic asphaltene-deposition process, the core permeability to the live mixture decreased in the first few cycles but appeared to stabilize after Cycle 5. The deposited asphaltenes were analyzed further through environmental scanning electron microscopy (ESEM), and their deposition was confirmed by mass balance before and after the tests. Finally, a relationship was established between permeability reduction and asphaltene precipitation. The results from the asphaltene-deposition experiment show that for the sample, fluids, and conditions used, permeability is impaired as asphaltene flocculates and begins to coat the grain surfaces. This impairment reaches a plateau at approximately 40% of the initial permeability. Distribution of asphaltene along the core was measured at the end by segmenting the core and conducting solvent extraction on each segment. Our recommendation is numerical modeling of these test results and using this model to forecast the magnitude of the permeability impairment in a reservoir setting during miscible GI.

Composition, structure and properties of Mo-N coatings formed by the method of vacuum-arc plasma-assisted deposition

Abstract A possibility in principle is shown for varying the elemental and phase compositions of nanocrystalline Mo-N coatings, synthesized using vacuum-arc plasma-assisted method, by changing the discharge parameters of the assisting gas plasma source at the constant pressure and composition of an Ar/N2 gas mixture. It is found out that an increase in the gas-to-metal ion current density ratio from 0 to 3 gives rise to a nearly twofold increase of nitrogen concentration in the coating of the Mo-N system. It is determined that as the discharge current is increased, the main metal (Mo) phase in the coating is replaced by a nitride phase with a nitrogen deficit (Mo2N), and then by a stoichiometric MoN phase. It is shown that the coatings formed in the plasma-assisted modes do not practically contain any metallic phase. With an increase in the nitrogen concentration the coating hardness increases by up to a factor of 1.3 (up to 36 GPa) and the wear resistance increases by about a factor of 2.4 (wear rate up to 2.1·10−7 mm3N−1 m−1) compared to the parameters of the coatings deposited in the regimes without plasma assistance. All coatings of the Mo-N system, synthesized in the plasma-assisted regimes, possess multiphase compositions: β-Mo2N, γ-Мо2N, δ-MoN. As the nitrogen concentration is increased, the volume fraction of δ-MoN phase increases to 67%. At the maximum nitrogen concentration, the Mo-N coating structure becomes columnar (plate-like) in the entire coating volume. The MoN and Mo2N plates have nanometric sizes, they are parallel to each other and combined into alternating packs. All Mo-N coatings are nanostructured, with the average Mo2N(β + γ) and MoN crystallite sizes being 3–4 and 3–5 nm, respectively.

Effect of Pressure and Temperature on Microstructure of Self-Assembled Gradient AlxTi1−xN Coatings

The correlation between structural properties of Al-rich self-assembled nano-lamellar AlxTi1−xN coatings and process parameters used during their chemical vapor deposition (CVD) remains unexplored. For this article, two gradient AlxTi1−xN coatings were prepared by a stepwise increase in temperature and pressure in the ranges of 750–860 °C and 1.56 to 4.5 kPa during the depositions at a constant composition of the process gas mixture. The cross-sectional properties of the coatings were analyzed using X-ray nanodiffraction (CSnanoXRD) and electron microscopy. Experimental results indicate that the variation of the process parameters results in changes in microstructure, grain morphology, elastic strain, nanolamellae’s chemistry and bi-layer period. At temperatures of ~750–800 °C and pressures of 2.5–4.5 kPa, preferably cubic nanolamellar grains are formed, whose microstructure correlates with the build-up of tensile stresses, which become relaxed in coating regions filled with nanocrystalline grains. CSnanoXRD superlattice satellite reflections indicate the period of the cubic Al(Ti)N-Ti(Al)N bilayers, which changes from 6.7 to 9 nm due to the temperature increase from 750 to ~810 °C, while it remains nearly unaffected by the pressure variation. In summary, our study documents that CVD process parameters can be used to tune microstructural properties of self-assembled AlxTi1−xN nanolamellae as well as the coatings’ grain morphology.

Differential Dissolution Stoichiographic Method in Investigation of the Chemical Composition of Functional Materials

This paper presents examples that characterize various aspects of the possibility of determining the phase composition of solid multielement substances and materials containing nanostructured forms of their components by a differential dissolution stoichiographic method. The use of stoichiography makes it possible to detect and quantitatively determine both known and unknown crystalline and amorphous phases of constant and variable composition without standards of solid phases. The use of stoichiographic methods and ideas of nonequilibrium thermodynamics allows one to gain fundamentally new data on solid-state transformations of multielement, multiphase substances and materials.

On the conceptual design of the hybrid nanofiltration/distillation process in the production of alcohol-free beers

In this paper, the conceptual design of a hybrid process consisting of a dealcoholization task via nanofiltration followed by a permeate valorization task via distillation is deeply investigated for the case of a lager beer. To this end, we resorted to conceptual models of each task.The conceptual model of the nanofiltration task, which is built from experiments al lab scale with the membrane NF99 HF (Alfa Laval, Sweden), allows the proper modeling of the three consecutive sub-tasks in which the process is divided; namely, pre-concentration, constant volume diafiltration, and re-dilution. Estimation of the overall permeation coefficient and the variation of the osmotic pressure difference throughout the pre-concentration stage are key in the model development. For the scaling-up of the membrane unit, the pressure loss issue is taken into account. The result of this task is a beer with an alcohol content below 0.5% by volume.For the conceptual modeling of the distillation task, a pinch-based method is adopted to allow a proper estimation of the minimum energy demand of the task, with feasible separations constrained by the presence of the azeotrope ethanol-water. This task is divided into two consecutive sub-tasks. In the first stage the alcohol is recovered as an ethanol-water mixture to be used for on-site Gin production by operating the rectifier in constant distillate composition mode (and thus at variable reflux ratio). In the second stage, operated at a constant reflux ratio, both the second cut, which is recycled to the next batch, and the water-rich content in the still at the end of the distillation step, which is recycled to the subsequent nanofiltration stage, are obtained.Economic and environmental performance of the hybrid process is compared with that of a case base with both units operating as standalone processes. In the latter case, the water-rich content in the still at the end of the distillation step is treated in a biological treatment plant on-site.Applied to an annual production of 720000 L of alcohol-free beer, the total cost of the standalone variant was 193600US$/year while the cost of the hybrid process was 205500US$/year; that is, 6.2% higher. On the other hand, and according to the life cycle assessment carried out, the Hybrid process has a lower environmental load. Results analyzed as a whole indicate the appropriateness of the Hybrid process.

Refinement of the Phase Diagram of the Bi-Te System and the Thermodynamic Properties of Lower Bismuth Tellurides

Alloys of the system Bi-Te obtained by long-term thermal annealing of samples quenched from 1000 K were studied by differential thermal analysis, x-ray phase diffraction, and scanning electron microscopy methods, as well as by electromotive forces measurements (EMF) of concentration cells relative to a bismuth electrode. A new refined version of the phase diagram which reflects the compounds Bi2Te3, Bi4Te5, Bi8Te9, BiTe, Bi4Te3, Bi2Te, and Bi7Te3 with practically constant compositions was constructed. It was found that all of these compounds, except for Bi2Te3, melt with decomposition by peritectic reactions. Based on powder diffraction patterns, the types and parameters of the crystal lattices of these compounds were determined. The EMF measurements were used to determine the partial molar functions of bismuth in the alloys and the standard integral thermodynamic functions of bismuth tellurides.

Configurational Geometry Bridges Equilibrium Structure Information from a Single to Multiple Compositions for Binary Discrete Systems

For substitutional alloys typically referred to as classical discrete systems under constant composition, a set of microscopic states dominantly contributing to thermodynamically equilibrium struct...

Optimal proteome allocation and the temperature dependence of microbial growth laws

Although the effect of temperature on microbial growth has been widely studied, the role of proteome allocation in bringing about temperature-induced changes remains elusive. To tackle this problem, we propose a coarse-grained model of microbial growth, including the processes of temperature-sensitive protein unfolding and chaperone-assisted (re)folding. We determine the proteome sector allocation that maximizes balanced growth rate as a function of nutrient limitation and temperature. Calibrated with quantitative proteomic data for Escherichia coli, the model allows us to clarify general principles of temperature-dependent proteome allocation and formulate generalized growth laws. The same activation energy for metabolic enzymes and ribosomes leads to an Arrhenius increase in growth rate at constant proteome composition over a large range of temperatures, whereas at extreme temperatures resources are diverted away from growth to chaperone-mediated stress responses. Our approach points at risks and possible remedies for the use of ribosome content to characterize complex ecosystems with temperature variation.

IM/DD probabilistically shaped 64-QAM OFDM-PON transmission assisted by selective-mapping and flexible systematic polar code

Intensity-modulation direct-detection (IM/DD) orthogonal frequency division multiplexing (OFDM) has advantages of low cost and simple structure, which is a promising candidate for next-generation high-speed passive optical networks. In this work, we propose and experimentally demonstrate a look-up-table-based probabilistic shaping scheme assisted by selective-mapping (SLM) and flexible systematic polar code (SPC) to improve the performance of IM/DD 64-QAM OFDM transmission system. Meanwhile, we experimentally compare the performance between the proposed scheme and the joint constant composition distribution matching (CCDM) and low-density parity-check (LDPC). Here, abundant phase sequences in the SLM are generated by chaotic sequence to suppress peak-to-average power ratio (PAPR). The pre-set bits of SPC are utilized for the additional information of probabilistic shaping to reduce the redundancy and the cyclic redundancy check (CRC) aided successive cancellation list (CA-SCL) decoder is used for decoding. Joint probabilistic shaping and PAPR suppression have contributed 4.6-dB and 3-dB bit error ratio performance improvements for the IM/DD 64-QAM OFDM transmission system in the pre and post forward error correction (FEC), respectively.

Effects of Synthesis Parameters on Organic Template-Free Preparation of Zeolite Y

In this work, the effects of reaction conditions on the conventional hydrothermal synthesis and crystal growth kinetics of zeolites Y in aqueous sodium alkaline solutions without the use of organic templates were studied. For this purpose, a series of Y-type zeolites were synthesized at different reaction conditions such as various aging temperatures, crystallization temperatures, Na2O contents of the initial gel and crystallization times using hydrothermal process. The prepared samples were well characterized by the X-ray diffraction (XRD) and N2 adsorption–desorption techniques. The results prove that the Na2O contents of the initial gel and synthesis temperature increase the rate of the Y and P zeolite crystallization. The effect of Na2O and temperature on the synthesis of two different zeolite types (Y and P) with a constant initial synthetic composition under the organic template-free synthesis of zeolite Y was studied. In inappropriate conditions, the P-type zeolite was the major impurity obtained along with the Y-type zeolite. Also from the experimental results, the kinetic parameters for both zeolite Y and zeolite P were calculated. The kinetic study show that the activation energy for crystallization of both zeolites was enhanced by increasing the Na2O content of the initial gel due to the structure-directing role of Na+ cation in the induction period and crystal growth step.

The influence of Ca:CO3 stoichiometry on Ca isotope fractionation: Implications for process-based models of calcite growth

The solution stoichiometry dependence of calcium isotope fractionation during calcite precipitation was investigated as a direct test of the conceptual model of calcium isotope discrimination driven by Ca exchange at surface sites during growth. Classical ion-by-ion models of calcite growth predict a strong solution stoichiometry influence on Δ44/40Cacalcite-fluid: In low Ca2+:CO32–solutions,Δ44/40Cais predicted to approach a kinetic limit (∼−2 to −4‰), while in high Ca2+:CO32–solutions, exchange at dominantly Ca-occupied kink sites drives Δ44/40Catowards the equilibrium fractionation (near 0‰). To test thisprediction,a series ofseeded and unseeded constant composition calcite growth experiments were performed in which all aspects of solution chemistry were held constant and the Ca2+:CO32– activity ratio was varied. Experiments were performed at pH 8.5, ionic strength 0.1 M (adjusted with KCl), and calcite saturation index (SI = log10({Ca2+}{CO32–}/Ksp)) of either 0.5 or 0.8.Calcium isotope fractionation is found to be weakly stoichiometry dependent. The expected trend of larger magnitude fractionations at lower Ca2+:CO32– is observed, but the magnitude of change in Δ44/40Ca over the solution stoichiometries studied (Ca2+:CO32– = 1–250) is only ∼ 0.4‰. Similar trends in Δ44/40Ca with Ca2+:CO32– are observed at SI = 0.5 and 0.8, with smaller magnitude fractionations at lower supersaturation. This yields an inverse correlation between Δ44/40Ca and growth rate, confirming the Δ44/40Ca-rate relationship for inorganic calcite growth observed by Tang et al. (2008). The ion-by-ion model framework captures measured Δ44/40Ca only when a surface complexation model is incorporated, highlighting the role of surface speciation in dictating Ca attachment/detachment dynamics. The model captures observed trends with Ca2+:CO32– using best-fit kinetic and equilibrium fractionations consistent with end-members observed in natural systems (αkinetic ∼ 0.9978, αeq ∼ 0.9998). This result implies a total possible range in Δ44/40Ca of 2‰ and suggests that for most carbonate precipitating environments, solution supersaturation will be a stronger determinant of Δ44/40Ca than stoichiometry. The demonstrated importance of surface speciation, however, implies a strong pH influence on Δ44/40Ca, independent of its influence on carbonate ion activity, that requires further investigation.The results of this study provide strong evidence supporting the model of kink-exchange driven Ca isotope fractionation and suggest that calcite grows by a dominantly classical mechanism over the solution conditions investigated. Model predictions regarding the relationship between Δ44/40Ca and growth inhibition in the presence of impurity ions lay the foundation for the use of Ca isotopes as molecular tracers of carbonate crystal growth pathways.

The Effect of Initial Conditions on the Laminar Flame Front Velocity in Gas Mixtures

In this paper, we consider the scatter of the laminar flame front velocities caused both by an error in the composition of the combustible mixture and by artificial initial disturbances. It is shown how the configuration of the initial perturbations of an initially flat front of a laminar flame in a gas mixture with the constant composition affects the velocity spread of expanding spherical flames. The effect of the error in the composition of the combustible mixture on the parameters that determine the flame front velocity was analyzed from the literature data on the spread of the flame propagation velocity. These parameters were recalculated for the possible variation in the mixture composition obtained based on the data on the accuracy of the equipment used in the experiments.

Experimental and numerical studies of non-equilibrium solvent exsolution behavior and foamy oil stability under quiescent and convective conditions in a visualized porous media

Non-equilibrium solvent exsolution and foamy oil stability in a visualized porous-media have been investigated. Two flow conditions were applied, namely, Static Constant Composition Expansion (SCCE) and Continuously Convective Flowing (CCF) schemes. The two schemes were aimed to study foamy oil non-equilibrium phase behavior deviating from the vapor–liquid-equilibrium under quiescent and convective condition, respectively. Two SCCE schemes, by both continuous and step-wise pressure depletion, were conducted. The non-equilibrium vapor phase volume ratio of the system was recorded, quantified and compared with the equilibrium state. Certain percentages from 5 to 35% of vapor-phase-ratio deviation from the equilibrium state were consistently found at multiple differentials from live oil saturation pressure. CCF tests up to 20 differentials from live oil saturation pressure were conducted to study non-equilibrium exsolution behavior under convection. Vapor phase volume ratio in CCF tests was always found to be 5–40% lower than that of the SCCE tests at the same operating pressure. Numerically, a MATLAB optimization module was developed to couple with CMG STARS reservoir simulator to study the non-equilibrium solvent exsolution behavior. Pseudo-chemical reaction kinetics representing non-equilibrium interphase mass transfer were applied. Gassy-liquid (compressible dispersed phase in a pseudo-single phase flow) and non-gassy-liquid (two-phase flow) schemes were implemented to history match the vapor phase volume ratio. The simulation results verified the phase-volume-ratio deviation from the equilibrium state in both SCCE and CCF schemes. Consistent to the experimental findings, the optimized kinetic reaction rate frequency factors indicated higher foamy oil stability under convective condition than that of quiescent condition.

A modified gas flow model in the near wellbore region below dew point pressure

When pressure in gas reservoirs fall below the dew point, condensate banking occurs around the wellbore which alters the fluid flow behavior. The state of the knowledge on this flow behavior is yet not fully-developed; which leads to severe problems in field. In this study, the Al-Hussainy, Ramey, and Crawford Solution Technique has been modified to accurately resemble the real gas flow behavior for this condition. First, a primary investigation was conducted to observe the severity of the problem in three condensate banked reservoirs. Then this study involved Constant Composition Expansion tests for determining the dew point, Prode Properties software for modeling the reservoir fluid properties, Flowing Material Balance (or Dynamic P/Z Material Balance) for identifying the pressure distribution of the selected reservoirs. The real field data along with the determined (analytical, computational, and experimental) data were incorporated to check the validity of the models. The modification proposes a Dimensionless Correction Factor (CD) for any condensate banked reservoir and identifies parameters such as the Perforation Factor (Pf) and Heterogeneity Factor (n). It is found that the Modified Al-Hussainy, Ramey, and Crawford Solution Technique successfully models the actual flow characteristics of the stated condition.