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Showing papers by "ExxonMobil published in 1995"


Journal ArticleDOI
TL;DR: A novel method for measuring the linear viscoelastic properties of a complex fluid over an extended range of frequencies is presented, showing that the response of the fluid to thermal fluctuations, as probed by the average motion of small particles dispersed within the fluid, provides a close representation of theresponse of the bulk fluid to an imposed shear strain.
Abstract: In this Letter, we present a novel method for measuring the linear viscoelastic properties of a complex fluid over an extended range of frequencies. We show that the response of the fluid to thermal fluctuations, as probed by the average motion of small particles dispersed within the fluid, provides a close representation of the response of the bulk fluid to an imposed shear strain. The essential physics of this approach is that the bulk mechanical susceptibility of the fluid determines the response of a small particle excited by the thermal stochastic forces which lead to Brownian motion. We use dynamic light scattering to measure the mean square displacement of a probe particle, kDr 2 stdl, and relate this to G p svd by describing the motion of the particle with a generalized Langevin equation, incorporating a memory function to account for the viscoelasticity. We compare this G p svd to that measured by conventional mechanical means. Remarkably good agreement is found. We demonstrate the flexibility of this new technique by measuring the moduli of a variety of complex fluids, and illustrate its potential to determine new behavior. We describe the motion of a small, neutrally buoyant particle dispersed in a complex fluid by means of generalized Langevin equation [2,3],

1,407 citations


Journal ArticleDOI
28 Jul 1995-Science
TL;DR: In this model, the fluctuations in the force distribution arise because of variations in the contact angles and the constraints imposed by the force balance on each bead in the pile.
Abstract: Experimental observations and numerical simulations of the large force inhomogeneities present in stationary bead packs are presented. Forces much larger than the mean occurred but were exponentially rare. An exactly soluble model reproduced many aspects of the experiments and simulations. In this model, the fluctuations in the force distribution arise because of variations in the contact angles and the constraints imposed by the force balance on each bead in the pile.

661 citations


Journal ArticleDOI
Glenn L. Bowers1
TL;DR: In this article, a new method for estimating pore pressure from formation sonic velocity data is presented, which accounts for excess pressure generated by both undercompaction, and fluid expansion mechanisms such as aquathermal pressuring, hydrocarbon maturation, clay diagenesis, and charging from other zones.
Abstract: A new method for estimating pore pressure from formation sonic velocity data is presented. Unlike previous techniques, this method accounts for excess pressure generated by both undercompaction, and fluid expansion mechanisms such as aquathermal pressuring, hydrocarbon maturation, clay diagenesis, and charging from other zones. The method is an effective stress approach; the effective stress is computed from the velocity, and the result is subtracted from the overburden stress to obtain pore pressure. to include multiple sources of overpressure, a pair of velocity-vs.-effective-stress relations are introduced. One relation accounts for normal pressure and overpressure caused by undercompaction. The second is applied inside velocity reversal zones caused by fluid expansion mechanisms. Example applications of the method are presented from the U.S. gulf coast, the Gulf of Mexico, and the Central North Sea. some other pore pressure estimation approaches are also examined to demonstrate how these techniques have unknowingly accounted for overpressure mechanisms other than undercompaction. It is also explained how velocity-vs.-effective-stress data can be used to identify the general cause of overpressure in an area. For instance, the empirical correlation of Hottman and Johnson indicates that overpressure along the US gulf coast cannot be due only to undercompaction.

547 citations


Journal ArticleDOI
TL;DR: The elastic shear modulus of monodisperse emulsions is shown to exhibit a universal dependence on droplet volume fraction f when scaled by the Laplace pressure of the droplets, increasing as fs f2f c d, where fc 0.635 is the value of random close packing of solid spheres.
Abstract: The elastic shear modulus of monodisperse emulsions is shown to exhibit a universal dependence on droplet volume fraction $\ensuremath{\varphi}$ when scaled by the Laplace pressure of the droplets, increasing as $\ensuremath{\varphi}(\ensuremath{\varphi}\ensuremath{-}{\ensuremath{\varphi}}_{c})$, where ${\ensuremath{\varphi}}_{c}\ensuremath{\approx}0.635$, the value of random close packing of solid spheres. Surprisingly the osmotic pressure required to compress the emulsions to increase $\ensuremath{\varphi}$ is nearly the same as the shear modulus over a large range of volume fraction, while the bulk osmotic modulus differs significantly. Models based on the structural disorder of the emulsions are discussed to account for these data.

468 citations


Journal ArticleDOI
TL;DR: The frequency-dependent viscoelastic shear modulus of concentrated suspensions of colloidal hard spheres is shown to be strongly modified as the volume fraction approaches the glass transition and a physical model is proposed to account for this data.
Abstract: The frequency-dependent viscoelastic shear modulus of concentrated suspensions of colloidal hard spheres is shown to be strongly modified as the volume fraction approaches the glass transition. The elastic or storage component, ${G}^{\ensuremath{'}}$, becomes larger than the viscous or loss component, ${G}^{\ensuremath{'}\ensuremath{'}}$. The frequency dependence of ${G}^{\ensuremath{'}}$ develops a plateau while that of ${G}^{\ensuremath{'}\ensuremath{'}}$ develops a minimum. We propose a physical model to account for these data, using a description of the glasslike behavior based on mode-coupling theory, and a description of the high-frequency behavior based on hydrodynamic flow calculations.

442 citations


Journal ArticleDOI
TL;DR: In this article, the Navier-Stokes equations were approximated to fourth-order accuracy with stencils extending only over a 3 x 3 square of points, and the key advantage of the new compact 4-order scheme is that it allows direct iteration for low-to-mediwn Reynolds numbers.
Abstract: SUMMARY We note in this study that the Navier-Stokes equations, when expressed in streamfunction-vorticity fonn, can be approximated to fourth--order accuracy with stencils extending only over a 3 x 3 square of points. The key advantage of the new compact fourth-order scheme is that it allows direct iteration for low~to-mediwn Reynolds numbers. Numerical solutions are obtained for the model problem of the driven cavity and compared with solutions available in the literature. For Re $1500 point-SOR iteration is used and the convergence is fast.

238 citations


Journal ArticleDOI
TL;DR: In this article, the authors proposed a new high temperature pathway for NO formation that involves the reaction of NNH with oxygen atoms, where the reaction formed the HNNO* energized adduct via a rapid combination reaction; the reaction then rapidly dissociates to NH + NO.
Abstract: We propose a new high temperature pathway for NO formation that involves the reaction of NNH with oxygen atoms This reaction forms the HNNO* energized adduct via a rapid combination reaction; HNNO* then rapidly dissociates to NH + NO The rate constant for O + NNH NH + NO is calculated via a QRRK chemical activation analysis to be 33 × 1014T−023exp(+510/T) cm3 mol−1 s−1 This reaction sequence can be an important or even major route to NO formation under certain combustion conditions The presence of significant quantities of NNH results from the reaction of H with N2 The H + N2 NNH reaction is only ca 6 kcal/mol endothermic with a relatively low barrier The reverse reaction, NNH dissociation, has been reported in the literature to be enhanced by tunneling Our analysis of NNH dissociation indicates that tunneling dominates We report a two-term rate constant for NNH dissociation: 30 × 108 + [M] {10 × 1013T05exp(−1540/T)} s−1 The first term accounts for pressure-independent tunneling from the ground vibrational state, while the second term accounts for collisional activation to higher vibration states from which tunneling can also occur ([M] is the total concentration in units of mol cm−3) Use of this dissociation rate constant and microscopic reversibility results in a large rate constant for the H + N2 reaction As a result, we find that NNH H + N2 can be partially equilibrated under typical combustion conditions, resulting in NNH concentrations large enough for it to be important in bimolecular reactions Our analysis of such reactions suggests that the reaction with oxygen atoms is especially important © 1995 John Wiley & Sons, Inc

234 citations


Patent
13 Dec 1995
TL;DR: In this article, a fuel oil composition comprising a major amount of fuel oil and a minor amount of an additive comprising at least one fuel oil-soluble alkyl or alkoxy aromatic compound was proposed.
Abstract: This invention provides a fuel oil composition comprising a major amount of a fuel oil and a minor amount of an additive comprising at least one fuel oil-soluble alkyl or alkoxy aromatic compound wherein at least one group independently selected from alkyl and alkoxy groups of 1 to 30 carbon atoms is attached to an aromatic nucleus and at least one carboxyl group and optionally one or two hydroxyl groups are attached to the aromatic nucleus; a process for the preparation of such a fuel oil composition; and the use of such a fuel oil composition as fuel in a compression-ignition engine for controlling wear rate in the fuel injection system thereof.

231 citations


Journal ArticleDOI
TL;DR: In this article, a new synthetic technique leads to sharp distributions of active sites near outer pellet surfaces by controlling the rate of imbibition of cobalt nitrate melts, leading to higher synthesis rates and C5+ selectivity.

197 citations


Journal ArticleDOI
TL;DR: The equilibrium compositions and structures of the phases of nearly-hardsphere binary colloids are investigated and experimental phase diagrams are obtained and predicted phase diagrams agree closely with the results of computer simulations and with the experimental results.
Abstract: We have investigated the equilibrium compositions and structures of the phases of nearly-hardsphere binary colloids and obtained experimental phase diagrams. Aqueous dispersions of chargestabilized polystyrene spheres were studied in the hard-sphere limit, with sphere-diameter ratios ranging from 2 to 12 and total volume fractions less than 0.4. At sufficiently high volume fractions, the samples separated into two phases. One phase, consisting primarily of small spheres, is a disordered fluid. In the other phase, the large spheres form an ordered crystalline solid which is permeated by a disordered fluid of small spheres. Previously reported crystallites on the surface of the sample cell were demonstrated to have the same structure as the bulk crystals and are assumed to be a wetting of the bulk phase. A simple model of the bulk phases is described and free energies calculated. The predicted phase diagrams agree closely .with the results of computer simulations and with our experimental results.

186 citations


Journal ArticleDOI
Haroon S. Kheshgi1
01 Sep 1995-Energy
TL;DR: In this paper, a preliminary analysis of a geoengineering option based on the intentional increase of ocean alkalinity to enhance marine storage of atmospheric CO2 is presented, and the potential feasibility and limits of such approaches are explored.

Journal ArticleDOI
17 Mar 1995-Science
TL;DR: The formation kinetics and self-assembly of multilamellar tubules of the diacetylenic phospholipid 1,2-bis(tricosa-10,12-diynoyl)-sn-glycerol-3-phosphocholine formed under controlled cooling rates are studied to form a highly efficient method of tubule production.
Abstract: The formation kinetics and self-assembly of multilamellar tubules of the diacetylenic phospholipid 1,2-bis(tricosa-10,12-diynoyl)-sn-glycerol-3-phosphocholine formed under controlled cooling rates were studied by x-ray diffraction and optical, atomic force, and scanning electron microscopy. Tubule formation was driven by a reversible first-order phase transition from an intralamellar, chain-melted L(alpha) phase to a chain-frozen L(beta), phase. These observations are the basis of a highly efficient method of tubule production in which tubule lengths can be controlled, between 1 and 100 micrometers, by varying the cooling rate. These tubules can be made in suspensions with 10 percent lipid by mass, far exceeding the lipid solubility limit.

Patent
13 Oct 1995
TL;DR: In this article, a process for producing a high Viscosity Index lubricant with a VI of at least 125 from a waxy hydrocarbon feed having a wax content of at most 40 wt.
Abstract: This invention discloses a process for producing a high Viscosity Index lubricant having a VI of at least 125 from a waxy hydrocarbon feed having a wax content of at least 40 wt.%. The process comprises catalytically dewaxing waxy paraffins present in the feed by isomerization in the presence of hydrogen and in the presence of a low acidity large pore zeolite isomerization catalyst. This catalyst has a ratio of SiO2/Al2O3, as synthesized, of at least 200:1, wherein the catalyst is prepared in the absence of boron. The feed may be hydrocracked prior to dewaxing with the large pore zeolite. The effluent of the process may also be further dewaxed by either solvent or catalytic means in order to achieve target pour point.

Patent
Carazzone James J1, David Chang1, Catherine Lewis1, Pravin M. Shah1, David Y. Wang1 
18 Aug 1995
TL;DR: In this paper, a method for deriving reservoir lithology and fluid content for a target location (400) from pre-stack seismic reflection data (110) was proposed, where the inversion process is preferably a viscoelastic inversion to account for the effects of friction on seismic wave propagation.
Abstract: A method for deriving reservoir lithology and fluid content for a target location (400) from pre-stack seismic reflection data (110). The method uses inversion (200) of pre-stack seismic reflection data for both the target location and a calibration location (110) having known subsurface lithology and fluid content to derive the subsurface lithology and fluid content at the target location (400). The inversion process (200) is preferably a viscoelastic inversion to account for the effects of friction on seismic wave propagation. The results of the inversion process are a set of subsurface elastic parameters for both the target and calibration locations. Relative magnitudes of these subsurface elastic parameters are compared (300), together with the known subsurface lithology and fluid content at the calibration location (146), to derive the subsurface lithology and fluid content at the target location (400).

Journal ArticleDOI
TL;DR: In this article, the structure and dynamics of fluid films confined to a thickness of a few molecular diameters are described, and a power law is found for a wide range of parameters, and extends to lower and lower velocities as a glass transition is approached.
Abstract: Simulations of the structure and dynamics of fluid films confined to a thickness of a few molecular diameters are described. Confining walls introduce layering and in-plane order in the adjacent fluid. The latter is essential to transfer of shear stress. As the film thickness is decreased, by increasing pressure or decreasing the number of molecular layers, the entire film may undergo a phase transition. Spherical molecules tend to crystallize, while short-chain molecules enter a glassy state with strong local orientational and translational order. These phase transitions lead to dramatic changes in the response of the film to imposed shear velocities v. Spherical molecules show an abrupt transition from Newtonian response to a yield stress as they crystallize. Chain molecules exhibit a continuously growing regime of non-Newtonian behavior where the shear viscosity drops as v−2/3 at constant normal load. The same power law is found for a wide range of parameters, and extends to lower and lower velocities as a glass transition is approached. Once in the glassy state, chain molecules exhibit a finite yield stress. Shear may occur either within the film or at the film/wall interface. Interfacial shear dominates when films become glassy and when the film viscosity is increased by increasing the chain length.

Proceedings ArticleDOI
TL;DR: In this article, the authors evaluated the historical frequency and severity of productivity impairment due to near-wellbore condensate buildup and identified reservoir parameters associated with severe productivity and recovery reduction.
Abstract: The depletion of gas condensate reservoirs to pressures below the dew point has been studied by reservoir engineers for many years. Pressure decline below the dew point pressure causes condensation to occur which creates a hydrocarbon liquid saturation in the reservoir. This process reduces liquid recovery and may reduce gas productivity and gas recovery. Exxon experience, particularly in low-productivity, high-yield gas condensate fields, suggests that liquid condensate formation can result in severe loss of well deliverability and therefore of gas recovery. This study was undertaken to evaluate the historical frequency and severity of productivity impairment due to near-wellbore condensate buildup and to identify reservoir parameters associated with severe productivity and recovery reduction. This study of gas condensate reservoirs included a survey of Exxon and published industry experience, a review of published laboratory data, and simulations with single well flow models. Data from 17 fields are included in this paper to demonstrate that severe loss of gas recovery occurs primarily in low productivity reservoirs. Production data from two wells were history matched with simple radial models to evaluate the potential range of the critical condensate saturation (the minimum mobile condensate saturation) and its impact on gas recovery. Published laboratory data for gas-condensate relative permeability were used as a starting point for these simulations. The primary conclusion from this study is that productivity impairment results in reductions in gas recovery for wells with a permeability-thickness below 1000 md-ft. The history matched simulations support a range of critical condensate saturations from 10% to 30%, in good agreement with published laboratory values.

Journal ArticleDOI
TL;DR: In this paper, the spectral boundary element method is employed to compute the resistance force for torque-free bodies in three cases: rigid solids, fluid droplets, and bubbles with viscosity ratio λ = 0.9, and a lubrication theory is developed to predict the limiting resistance of bodies near contact with the cylinder walls.
Abstract: Numerical computations are performed to evaluate the resistance functions for low Reynolds number flow past spherical particles, droplets and bubbles in cylindrical domains. Spheres of arbitrary radius a and radial position b move with arbitrary velocity U within a cylinder of radius R. The undisturbed fluid may be at rest, or subject to a pressure-driven flow with maximum velocity U 0 . The spectral boundary element method is employed to compute the resistance force for torque-free bodies in three cases : rigid solids, fluid droplets with viscosity ratio λ = 1, and bubbles with viscosity ratio λ = 0. A lubrication theory is developed to predict the limiting resistance of bodies near contact with the cylinder walls. Compact algebraic expressions are developed which accurately represent the numerical data over the entire range of particle positions 0 < b/(R-a) < 1 for all particle sizes in the range 0 < a/R < 0.9. The resistance functions are consistent with known analytical results and are presented in a form suitable for further studies of particle migration in cylindrical vessels.

Journal ArticleDOI
TL;DR: In this article, micro-phase separation and subsequent crystallization in an ethylene/head-to-head propylene (E/hhP) diblock copolymer using time-resolved small-and wide-angle X-ray scattering (SAXS and WAXS) were studied.
Abstract: Microphase separation and subsequent crystallization are studied in an ethylene/head-to-head propylene (E/hhP) diblock copolymer using time-resolved small- and wide-angle X-ray scattering (SAXS and WAXS). When the sample is cooled from the melt, the SAXS data show a broad maximum due to correlation-hole scattering, which is replaced by a single sharp Bragg reflection due to the melt microstructure. During subsequent crystallization, two higher-order reflections grow concurrently. Thus, for similar quench depths below the microphase separation transition (T MST ) and the melting temperature (T m ) respectively, microstructures representative of weak and strong segregation are observed. The second-and third-order reflections are superimposed on an intense broad maximum arising from the heterogeneity within the semicrystalline E domains. The second- and third-order SAXS peaks and the broad maximum on which they are superimposed, none of which are visible prior to crystallization, grow in parallel with the development of crystallinity at the unit cell level observed by WAXS. The overall domain periodicity d increases during crystallization but its value is path dependent and varies with the cooling rate from the melt.

Journal ArticleDOI
TL;DR: Powder-neutron-diffraction studies of the antiferromagnetic order that develops below 6.8 K in the magnetic superconductor reveal a squared-up sine wave, with a low-temperature amplitude of 7.8% for the Er atom and evidence of an induced moment of -0.35 on the Ni ions.
Abstract: We have carried out powder-neutron-diffraction studies of the antiferromagnetic order that develops below ${\mathit{T}}_{\mathit{N}}$=6.8 K in the magnetic superconductor (${\mathit{T}}_{\mathit{c}}$=11 K) ${\mathrm{ErNi}}_{2}$${\mathrm{B}}_{2}$C. The antiferromagnetic structure is associated with spins on the Er atoms, which order in a transversely polarized planar sinusoidal structure propagating along the a or b axis in equal domains, with the Er moments parallel to the b or a axis, respectively. Third and fifth harmonics of the sine wave are observed at low temperatures, indicating a squared-up sine wave, with a low-temperature amplitude of 7.8${\mathrm{\ensuremath{\mu}}}_{\mathit{B}}$/Er atom. There is also evidence of an induced moment of -0.35${\mathrm{\ensuremath{\mu}}}_{\mathit{B}}$ on the Ni ions. A similar study of the isostructural compound ${\mathrm{YNi}}_{2}$${\mathrm{B}}_{2}$C revealed no magnetic peaks (\ensuremath{\mu}0.13${\mathrm{\ensuremath{\mu}}}_{\mathit{B}}$) developing down to 0.3 K for Q values less than 1.6 A${\mathrm{\r{}}}^{\mathrm{\ensuremath{-}}1}$.

Journal ArticleDOI
TL;DR: In this paper, the authors analyzed sulfur K-edge X-ray absorption near-edge structures (XANES) and demonstrated that sulfur is present in a variety of biogenic and diagenetic carbonates as sulfate.

Journal ArticleDOI
TL;DR: It is shown that in an applied field the liquid droplets within the two-phase coexistence region become elongated in the direction of the field, and the critical densities change very little as a function of applied field.
Abstract: We examine two apects of Stockmayer fluids, which consist of point dipoles that additionally interact via an attractive Lennard-Jones potential. We perform Monte Carlo simulations to examine the effect of an applied field on the liquid-gas phase coexistence and show that a magnetic fluid phase does exist in the absence of an applied field. As part of the search for the magnetic fluid phase, we perform Gibbs ensemble simulations to determine phase coexistence curves at large dipole moments, \ensuremath{\mu}. The critical temperature is found to depend linearly on ${\mathrm{\ensuremath{\mu}}}^{2}$ for intermediate values of \ensuremath{\mu} beyond the initial nonlinear behavior near \ensuremath{\mu}=0 and less than the \ensuremath{\mu} where no liquid-gas phase coexistence has been found. For phase coexistence in an applied field, the critical temperatures as a function of the applied field for two different \ensuremath{\mu} are mapped onto a single curve. The critical densities change very little as a function of applied field. We also verify that in an applied field the liquid droplets within the two-phase coexistence region become elongated in the direction of the field.

Patent
24 Jan 1995
TL;DR: In this article, a supported particulate cobalt catalyst is formed by dispersing cobalt, alone or with a metal promoter, particularly rhenium, as a thin catalytically active film upon a particulate support, especially a silica or titania support.
Abstract: A supported particulate cobalt catalyst is formed by dispersing cobalt, alone or with a metal promoter, particularly rhenium, as a thin catalytically active film upon a particulate support, especially a silica or titania support. This catalyst can be used to convert an admixture of carbon monoxide and hydrogen to a distillate fuel constituted principally of an admixture of linear paraffins and olefins, particularly a C10+ distillate, at high productivity, with low methane selectivity. A process is also disclosed for the preparation of these catalysts.

Journal ArticleDOI
TL;DR: The application of the diffusion approximation to describe the propagation of ultrasonic waves through a random, strongly scattering medium and the absolute transmitted intensity of the sound as the sample thickness is varied are demonstrated.
Abstract: We have critically tested the application of the diffusion approximation to describe the propagation of ultrasonic waves through a random, strongly scattering medium. The transmission of short ultrasonic pulses has been measured through a concentrated suspension of glass beads immersed in water. The transmitted sound field is found to exhibit temporal fluctuations with a period determined by the width of the incident pulse. Provided that appropriate boundary conditions are used to account for the reflectivity of the interfaces, the time dependence of the ensemble-averaged transmitted intensity is shown to be well described by the diffusion equation. This enables us to determine both the diffusion coefficient for the sound waves as well as the inelastic absorption rate. The consistency of these results is established by varying the experimental geometry; while the transmitted pulse shape changes markedly, the values for the diffusion coefficient and absorption rate obtained through a description using the diffusion approximation remain unchanged. We have also measured the absolute transmitted intensity of the sound as the sample thickness is varied; this provides an accurate measure of the transport mean free path and thus also the energy transport velocity. These results convincingly demonstrate the validity of using the diffusion approximation to describe the propagation of sound waves through strongly scattering media.

Journal ArticleDOI
P. Peczak1
TL;DR: In this article, a simulational procedure that models dynamic recrystallization and recovery in polycrystals has been proposed, where the combined effects of deformation and elevated temperatures, which are interrelated by the Zener-Hollomon parameter, Z=∈exp(Qact/RT), are simulated by adding stored energy and recrystization nuclei continuously with time.
Abstract: Recently, simulational procedure that models dynamic recrystallization and recovery in polycrystals has been proposed. The combined effects of deformation and elevated temperatures, which are interrelated by the Zener—Hollomon parameter, Z=∈exp(Qact/RT, are simulated by adding stored energy and recrystallization nuclei continuously with time. The experimentally observed spatial inhomogeneity of the dislocation density within grains is represented by a probabilistic expression for the stored energy distribution. The simulated transient and steady-state recrystallization parameters' relationships agree very well with experimental observations. The microstructures obtained in the simulations at Z = const and their properties are almost identical. The observations vindicate the description of dynamic recrystallization as a “simultaneous static recrystallization”. A careful analysis of simulational data demonstrates very good quantitative agreement between our results and those found in experiment.

Journal ArticleDOI
TL;DR: In this article, Fe-Zn oxides promoted with K and Cu selectively produce α-olefins at typical Fischer-Tropsch synthesis conditions (2/1 H2/CO, 1 MPa, and 270°C).
Abstract: Fe/Zn oxides promoted with K and Cu selectively produce α-olefins at typical Fischer-Tropsch synthesis conditions (2/1 H2/CO, 1 MPa, and 270°C). The simultaneous presence of K and Cu introduces a synergistic activity enhancement while maintaining the high olefin selectivity obtained by alkali promotion. Structural and morphological differences in Fe-Zn oxides prepared from ammonium glycolate complexes or precipitated from nitrate solutions have only a small influence on catalytic properties. Catalyst behavior is strongly influenced by synergistic promoter effects (Cu, K) and by the controlled in situ conversion of iron oxide precursors to carbides.

Journal ArticleDOI
TL;DR: In this paper, the early cementation associated with these marine flooding surfaces occurred as a result of reduced sediment accumulation rates or non-depositional hiatuses linked to abrupt deepening during marine flooding.
Abstract: Field data from the Upper Cretaceous Blackhawk Formation in the Book Clitfs (Utah–Colorado) demonstrate the presence of laterally extensive carbonate cements beneath major marine flooding surfaces. The occurrence of firmgrounds, compaction around concretions, and high minus-cement porosities indicate that cementation occurred during early diagenesis. It is proposed that the early cementation associated with these marine flooding surfaces occurred as a result of reduced sediment accumulation rates or non-depositional hiatuses linked to abrupt deepening during marine flooding. These reduced sediment accumulation rates extended sediment residence time within early diagenetic zones, leading to enhanced early cementation in shallow marine sandstones and mudstones.

Journal ArticleDOI
TL;DR: In this paper, the adsorption and desorption of hexane in porous Vycor, as the ambient vapor pressure is varied, through sorption isotherm, ultrasonic velocity and attenuation, and light scattering measurements.
Abstract: We study the adsorption and desorption of hexane in porous Vycor, as the ambient vapor pressure is varied, through sorption isotherm, ultrasonic velocity and attenuation, and light scattering measurements. On adsorption, we show that the fluid fills the pore space uniformly until capillary condensation occurs; however, small, randomly distributed, vapor bubbles remain, as detected by a large increase in the attenuation of the ultrasound. On desorption, the mismatch in the index of refraction between the empty pores and the surrounding filled pores leads to intense scattering of light that reveals the presence of long-range correlations in the pore space. These correlations have a fractal dimension of 2.6, which is very near the value predicted for invasion percolation. Finally, we also investigate the time dependence of the changes in the adsorbed fluid mass and use these measurements to identify three distinct regimes with vastly differing mechanisms for mass transport. The results presented here provide information on the differences in pore-space correlations on filling and drainage, and highlight the critical role of the connectivity of the pores to the surface in determining the desorption behavior.

Journal ArticleDOI
E.M. Braun1, R.F. Holland1
TL;DR: In this article, relative permeability hysteresis measured for a water-wet outcrop outcrop rock sample and a mixedwet reservoir core and the authors proposed a mechanism for the reversible behavior is pinning of water/oil interfaces on surfaces of rock grains.
Abstract: Relative permeability hysteresis has been measured for a water-wet outcrop rock sample and a mixed-wet reservoir core. For the oil phase, imbibition and drainage relative permeability curves differed significantly. The difference was much less pronounced for the water phase. Scanning curves, which characterize transitions between imbibition and drainage curves, were also measured. A notable characteristic of the oil relative permeability scanning curves is their reversibility; along most of the length of a scanning curve, oil relative permeability exhibits no hysteresis. A proposed mechanism for the reversible behavior is pinning of water/oil interfaces on surfaces of rock grains. Pinned interfaces remain anchored at fixed positions on grains despite changes in interface curvature and contact angle. In water-wet samples, pinning can occur as a result of contact-angle hysteresis. In mixed-wet rock, pinning can occur at the boundaries between water- and oil-wet grain surfaces. As long as interfaces remain pinned, pore-level fluid geometry is a function of saturation only and does not depend on the directional of saturation change.

Journal ArticleDOI
TL;DR: In this paper, the conformation changes of polyaniline doped with camphor sulfonic acid (CSA) in m-cresol were studied with dynamic light scattering.

Journal ArticleDOI
H.B. Lo1, Brian J. Cardott
TL;DR: In this article, the authors apply routine geochemical analyses (including organic petrography) to coal and shale samples, extending from the weathered to unaltered zones, to illustrate the effects of weathering on organic matter.