Showing papers by "ExxonMobil published in 1983"

Diffusion-limited aggregation

Abstract: Diffusion-limited aggregation (DLA) is an idealization of the process by which matter irreversibly combines to form dust, soot, dendrites, and other random objects in the case where the rate-limiting step is diffusion of matter to the aggregate. We study the process from several points of view stressing the fact that it apparently gives rise to scale-invariant objects whose Hausdorff dimension is independent of short-range details. We show that DLA has no upper critical dimension. We apply scale invariance to study growth, gelation, and the structure factor of aggregates.

Interpretation of well-block pressures in numerical reservoir simulation with nonsquare grid blocks and anisotropic permeability

Abstract: An interpretation is given of well-block pressure for the case of nonsquare grid blocks. Based on numerical solutions for the single-phase five-spot problem, using various sizes of grids, a relationship is established for the effective well-block radius (where the actual flowing pressure equals the numerically calculated well-block pressure). This relationship is verified by a mathematical derivation for a single well in an infinite grid. Finally, the analysis is extended to include anisotropic permeability. 11 refs.

Rheology of foams and highly concentrated emulsions

Abstract: Expressions are derived for certain rheological properties, such as the stress vs strain relationship, yield stress, and shear modulus, of monodisperse foams and highly concentrated emulsions for the model of infinitely long cylindrical drops (or bubbles). The variables considered are the volume fraction of the dispersed phase, the drop radius, the interfacial tension, the thickness of the films separating adjacent drops, and the films' associated contact angle. Both the yield stress and the shear modulus are proportional to the interfacial tension and inversely proportional to the drop radius. The yield stress increases sharply with increasing volume fraction, while the shear modulus varies as its square root. The effect of a finite contact angle, θ, is to decrease the shear modulus and, in most cases, to increase the yield stress. Finally, the effect of a finite film thickness is to always increase both the yield stress and the shear modulus. The implications of these results to real emulsions and foams are discussed.

Process and catalyst for producing polyethylene having a broad molecular weight distribution

Abstract: Polyolefins having a broad molecular weight distribution are obtained by polymerizing ethylene or higher alpha-olefins in the presence of a catalyst system comprising two or more metallocenes each having different propagation and termination rate constants and alumoxane.

In situ shale-oil recovery process

Abstract: Disclosed is a process for converting organic material of oil-shale to predominantly liquids. The oil-shale is first heated to a temperature from about 360° C. to 475° C. in an anionic atmosphere. The resulting liquids and gases are collected and the residue is extracted with a microemulsion capable of extracting organic material from the heat treated oil-shale.

High‐temperature mutual solubilities of hydrocarbons and water. Part I: Benzene, cyclohexane and n‐hexane

Abstract: The mutual solubilities at the three-phase equilibrium pressure of three C/sub 6/ hydrocarbons (benzene, cyclohexane and n-hexane) and water have been experimentally investigated up to 482 K. A thermodynamic analysis of these new measurements and of critically selected literature data has been carried out up to the three-phase critical end point. Information is also provided on the two-phase critical locus. The solubility of hydrocarbons in water has been used to calculate Henry's constants, while the solubility of water in the hydrocarbons has been correlated with a modified version of the Redlich-Kwong equation of state. Consideration is also given to the effect of pressure on the mutual solubilities.

Hopping conductivity in granular disordered systems

Abstract: We study the temperature dependence of conductivity for high-resistivity granular disordered systems in terms of the critical-path method. It is shown that the low-field conductivity $\mathrm{exp}(\ensuremath{-}\frac{A}{{T}^{\ensuremath{\alpha}}})$ with $\ensuremath{\alpha}=\frac{1}{2}$ is obeyed over large temperature ranges with possible crossovers to $\ensuremath{\alpha}=\frac{1}{4}$ at low temperatures and to $\ensuremath{\alpha}g\frac{1}{2}$ at high temperatures. The temperatures at which the crossovers occur depend on the distribution of grain sizes. Comparisons are made with experiments and with other theoretical approaches.

Method and apparatus for offshore electromagnetic sounding utilizing wavelength effects to determine optimum source and detector positions

Abstract: An improved method and apparatus for electromagnetic surveying of a subterranean earth formation beneath a body of water. An electric dipole current source is towed from a survey vessel in a body of water substantially parallel to the surface of the body of water and separated from the floor of the body of water by a distance less than approximately one-quarter of the distance between the surface and the floor. Alternating electric current, preferably including a plurality of sinusoidal components, is caused to flow in the source. An array of electric dipole detectors is towed from the survey vessel substantially collinearly with the current source. Each electric dipole detector of the array is separated from the current source by a distance substantially equal to an integral number of wavelengths of electromagnetic radiation, of frequency equal to that of a sinusoidal component of the source current, propagating in the water. A gradient detector array is also towed by the survey vessel in a position laterally separated from, or beneath, the mid-point of the current source. Additionally, an array of three-axis magnetic field sensors mounted in controllable instrument pods are towed by the seismic vessel on the flanks of the current source. Frequency-domain and time-domain measurements of magnetic and electric field data are obtained and analyzed to permit detection of hydrocarbons or other mineral deposits, or regions altered by their presence, within subfloor geologic formations covered by the body of water.

Phase Diagrams for Microemulsions

Abstract: A phenomenological mean-field model of globules for a three-component microemulsion is presented and typical phase diagrams are obtained. Two types of two-phase coexistence are found as well as a three-phase equilibrium. The topology of the phase diagram is determined by the ratio of the critical globule radius to the natural bending radius and by the radius dependence of the attractive interactions.

Bonding and bond lengths of chemisorbed molecules from near-edge X-ray absorption fine-structure studies

Abstract: Intramolecular scattering resonances in near-edge x-ray-absorption fine-structure spectra of chemisorbed molecules are used to determine the molecular orientation, bonding, and bond length. In particular, we demonstrate that the position of the $\ensuremath{\sigma}$ shape resonance relative to the Fermi level is directly correlated with the intramolecular bond length of the chemisorbed molecule. By comparison with the known molecular distances in the gas phase, changes induced by the chemisorption bond are revealed.

Hardened Subtidal Stromatolites, Bahamas

Abstract: Hardened, high-relief stromatolites have been discovered along the margins of some Bahamian platforms. They occur in high-energy (tidal) oolitic sand environments in waters ranging in depth from about 1 to 5 meters. Physical stress produced by actively migrating bed forms of oolitic sand appears to exclude grazing gastropods and subsequent community successions, permitting stromatolite growth.

Composition for reducing the permeability of subterranean formations

Abstract: The present invention relates generally to the composition and method for reducing the permeability of subterranean formations penetrated by a wellbore The composition of the present invention comprises a wellbore fluid having dispersed therein a fluid loss control agent comprising a polyester polymer which is substantially insoluble in the wellbore fluid The polymer degrades in the presence of water at an elevated temperature to form small molecules which are soluble in a fluid in the subterranean formation The method of the present invention comprises reducing the permeability of subterranean formations penetrated by a wellbore by placing the composition of the present invention down the wellbore

The Effects of Mechanical Degradation and Viscoelastic Behavior on Injectivity of Polyacrylamide Solutions

Abstract: Results of recent experiments that clarify the effects of mechanical degradation and viscoelastic behavior on the flow of partially hydrolyzed polyacrylamide solutions through porous media are presented. From these results, a simple model that may be used to predict injectivity of polyacrylamide solutions is developed. Injection pressures for linear corefloods are shown to be separable into two components: an initial pressure drop associated with the entrance of polymer into the sandstone and a constant pressure gradient throughout the remainder of the core. Entrance pressure drop is zero until the polymer solution flux increases to the rate where mechanical degradation takes place. Thereafter, entrance pressure drop and the degree of polymer mechanical degradation increase with increasing flux. These observations suggest that the entrance pressure drop is associated closely with the process of polymer mechanical degradation. A new correlation is developed that may be used to determine entrance pressure drop and the level of mechanical degradation directly as a function of sandface flux, permeability, and porosity. This correlation is more convenient to apply and less dependent on flow geometry than previous correlations. Based on these observations, a model is developed that may be used to estimate injectivity of polyacrylamide solutions in linearmore » or radial flow geometries.« less

In-situ retorting of oil shale

Abstract: Fluid, such as liquid water, is injected into the rock surrounding an in situ oil shale retort at sufficient pressure and flow rate so that the injected fluid flows toward the retort to block the path of hot liquid and gaseous kerogen decomposition products escaping from the retort and to return heat to the retort. The successful conduct of an oil shale retorting operation usually requires that the retort temperature be maintained at a temperature sufficient to decompose efficiently the kerogen contained in the oil shale. By reducing the heat loss from an active retort, the amount of energy required to maintain a desired temperature therein is reduced. The fluid injection method also maintains pressure in an in-situ oil shale retort, allowing in-situ oil shale retorting to be efficiently conducted at a desired pressure. The method also reduces the danger to mineworkers who may be engaged in adjacent mining operations due to the escape of hazardous gases from an active retort. The method allows a series of sequential in-situ oil shale retorts in an oil shale formation to be placed more closely together than previously practical by reducing hot fluid leakage from each active retort to one or more abandoned retorts adjacent thereto, thus improving the recovery factor from the formation. The method also minimizes contamination of the formation surrounding an active in-situ retort due to hazardous chemicals which may be contained in the kerogen decomposition products leaking from the retort.

Critical behavior of a microemulsion studied by small-angle neutron scattering

Abstract: The critical behavior of a three-component water-in-oil microemulsion was studied by small-angle neutron scattering. Intensity spectra were analyzed by the treatment of critical scattering as arising from concentration fluctuations of polydisperse spheres. We propose a model capable of fitting the data over five decades of intensity variation. The critical exponents were determined to be $\ensuremath{ u}=0.72\ifmmode\pm\else\textpm\fi{}0.04$ and $\ensuremath{\gamma}=1.61\ifmmode\pm\else\textpm\fi{}0.09$. The average droplet size and width of the size distribution exhibited little temperature dependence.

Coulomb effects on one-dimensional peierls instability: The peierls-hubbard model

Abstract: A novel approach to dimerization is developed, based on a many-body valence-bond approach, that predicts enhancement of the dimerization on inclusion of the on-site electron repulsion. Exact numerical calculations are presented to substantiate this conclusion.

Maximum statistical increase of optical absorption in textured semiconductor films.

Abstract: Complete statistical randomization of the direction of propagation of light trapped in semiconductor films can result in a large absorption enhancement. We have employed a calorimetric technique, photothermal deflection spectroscopy, to monitor the absorption of alpha-SiH(x) films textured by the natural lithography process. The observed enhancement factors, as high as 11.5, are consistent with full internal phase-space randomization of the incoming light.

Extraction of Uranium from Wet Process Phosphoric Acid by Liquid Membranes

Abstract: The liquid membrane process can effectively separate and concentrate uranium from wet process phosphoric acid and is economically superior to solvent extraction systems. The paper describes the process, compares it to other extraction schemes, and shows how it can be used for uranium recovery. A mathematical model useful for design purposes is presented and the effect of important variables is discussed.

On the application of the mode‐acceleration method to structural engineering problems

Abstract: Mode-superposition has been extensively used in computing the dynamic response of complex structures. Two versions of mode-superposition, namely the mode-displacement method and the mode-acceleration method, have been employed. The present paper summarizes the results of a systematic study comparing the accuracy of the mode-displacement and mode-acceleration methods when applied to structures with various levels of damping or various excitation frequencies. The paper also discusses several details concerning the implementation of the mode-acceleration method.

Isotactic-stereoblock polymers of alpha-olefins and process for producing the same

Abstract: Isotactic-stereoblock polypropylene comprising recurring polypropylene units, said isotactic-stereoblock polypropylene characterized by comprising alternating blocks of monomers having an average block length greater than 2 having methine carbons with the same relative configuration and wherein the methine carbon atoms in adjacent blocks are of opposite configuration.

Theory of photoelectron angular distributions in resonant multiphoton ionization

Abstract: In this paper, we present the theory of photoelectron angular distributions in resonant multiphoton ionization that rigorously takes into account the saturation, ac Stark-shift, and the laser-linewidth effects. The influence of these effects on the distribution is incorporated through the coupling equations between the angle-resolved ionization probabilities and the (time-dependent) bound-state density-matrix elements. General expressions for the angular distributions are derived and several properties of these distributions are arrived at from these expressions. Finally, numerical results are presented to illustrate the effects of saturation, of ac Stark shifts, and of the laser line shape.

Lithium-intercalated graphite: Self-consistent electronic structure for stages one, two, and three

Abstract: First-principles electronic structure calculations were carried out for Li${\mathrm{C}}_{6}$, Li${\mathrm{C}}_{12}$, and Li${\mathrm{C}}_{18}$ representing first-, second-, and third-stage model graphite intercalation compounds. By comparing the charge density of these compounds to that of reference graphite compounds, we could define a "total difference density" in order to quantify charge transfer and polarization in these materials. The total difference density is found to be highly concentrated near the intercalant ions. However, the conduction electrons (those in partially occupied bands) are found to have the distribution of virtually undistorted $\ensuremath{\pi}$ wave functions and have a much more delocalized distribution than that of the total difference density. These two types of charge distributions account for many of the unusual electronic properties of graphite intercalation compounds.