Gas Coexistence Research Articles

Interpreting structural controls on hydrate and free-gas accumulation using well and seismic information from the Gulf of Mexico

The effect of the structural setting on gas hydrate and free-gas accumulation near the East Casey fault zone at Keathley Canyon in the Gulf of Mexico is investigated using well logs and 2D and 3D acoustic-impedance inversions. We interpret two zones from the well logs: a probable hydrate zone and a dissociating hydrate zone. We interpret hydrates as fracture fillings in the clay-dominated formation with maximum saturation of approximately 30% of the available pore space, and maximum volumetric concentration of approximately 12%. The maximum free-gas concentration below the interpreted bottom simulating reflector (BSR) is less than 4%. Resistivity measurements alone are incon-clusive; complimentary measurements, such as sonic, reduce hy-drate interpretation ambiguities. Seismic data in 3D and the derived acoustic-impedance volume are interpreted in terms of a BSR, a high [Formula: see text]-impedance hydrate zone, and free gas. We interpret two bright, low [Formula: see text]-impedance features terminating at the BSR as free-gas accumulations. The contrast in average [Formula: see text]-impedance across the fault suggests a change in lithology across the fault zone, and free-gas transport along, and to the west of, the fault. Variations in depths of interpreted free-gas zones suggest either a significant lateral variation in the hydrate stability across the fault zone, or coexistence of hydrates and free gas within the hydrate stability zone, or both. The dynamics of the tectonic environment imply nonequilibrium conditions of time-dependent temperature, pressure, or fluid transport.

A numerical study of one-patch colloidal particles: from square-well to Janus

We perform numerical simulations of a simple model of one-patch colloidal particles to investigate: (i) the behavior of the gas-liquid phase diagram on moving from a spherical attractive potential to a Janus potential and (ii) the collective structure of a system of Janus particles. We show that, for the case where one of the two hemispheres is attractive and one is repulsive, the system organizes into a dispersion of orientationally ordered micelles and vesicles and, at low temperature (T), the system can be approximated as a fluid of such clusters, interacting essentially via excluded volume. The stability of this cluster phase generates a very peculiar shape of the gas and liquid coexisting densities, with a gas coexistence density that increases on cooling, approaching the liquid coexistence density at very low T.

Global importance of “continuous” petroleum reservoirs: Accumulation, distribution and evaluation

Abstract Based on distribution of oil and gas in the world, the connotation and characteristics of “continuous” petroleum reservoirs are elaborated in this paper. “Continuous” petroleum reservoirs refer to unconventional trap reservoirs existing in a large-scale unconventional reservoir system, and the distribution of oil and gas is continuous. The main geological characteristics of “continuous” petroleum reservoirs are as follows: located in the center and slope of a basin, large-scale distribution and rich locally; mainly of large-scale unconventional reservoirs; traps have no clear boundaries; mainly of self-generating and self-preserving; mainly of primary migration; accumulated by diffusion and buoyancy is limited; non-Darcy flow; poor oil-water differentiation and different saturation; oil, water and gas coexist and have no common interface and pressure system; resources abundance is low and reserves are calculated by well-control region; the mining technologies are special and tailored techniques are required. In this paper are discussed the cause of deep-water “sandy debris flow” and a few examples on “continuous” reservoirs, the shallow-water delta low or ultra-low porosity and permeability reservoirs, coal-bed methane and shale-cracked reservoirs and so on.

Posttraumatic intradural pneumorrhachis: A rare entity

Pneumorrhachis, denoting intra-spinal air, is an uncommon epiphenomenon of coincident underlying injuries and diseases, accompanied by different aetiologies and possible pathways of air entry into the spinal canal. Air within the spinal canal can be divided into primary and secondary pneumorrhachis, extra- or intradural pneumorrhachis and aetiologically subsumed into iatrogenic, traumatic and nontraumatic The pathogenesis and aetiologies of pneumorrhachis are multifold and can be a diagnostic challenge. CT is the imaging tool of choice. Pneumorrhachis has to be differentiated from free intraspinal gas collections and the coexistence of air and gas within the spinal canal has to be considered differential diagnostically. Pneumorrhachis usually is asymptomatic but can also be symptomatic by itself as well as by its underlying pathology. The latter, although often severe, might be concealed and has to be examined carefully to enable adequate patient treatment. The management of pneumorrhachis has to be individualized.

Morphological study of acoustic liposomes using transmission electron microscopy

Sonoporation is achieved by ultrasound-mediated destruction of ultrasound contrast agents (UCA) microbubbles. For this, UCAs must be tissue specific and have good echogenicity and also function as drug carriers. Previous studies have developed acoustic liposomes (ALs), liposomes that encapsulate phosphate buffer solution and perfluoropropane (C(3)F(8)) gas and function as both UCAs and drug carriers. Few studies have examined the co-existence of gas and liquid in ALs. This study aims to elucidate AL structure using TEM. The size, zeta potential and structure of ALs were compared with those of two other UCAs, human albumin shell bubbles (ABs; Optison) and lipid bubbles (LBs). ABs and LBs encapsulate the C(3)F(8) gas. Particle size was measured by dynamic light scattering. The zeta potential was determined by the Smoluchowski equation. UCA structure was investigated by TEM. ALs were approximately 200 nm in size, smaller than LBs and ABs. ALs and LBs had almost neutral zeta potentials whereas AB values were strongly negative. The negative or double staining TEM images revealed that approximately 20% of ALs contained both liquid and gas, while approximately 80% contained liquid alone (i.e. nonacoustic). Negative staining AB images indicated electron beam scattering near the shell surface, and albumin was detected in filament form. These findings suggest that AL is capable of carrying drugs and high-molecular-weight, low-solubility gases.

Mechanism of PdO thin film formation during the oxidation of Pd(1 1 1)

We investigated the mechanism by which a surface oxide layer on Pd(1 1 1) transforms to a PdO(1 0 1) thin film during oxidation with gaseous oxygen atoms in ultrahigh vacuum. Our results provide evidence that the precursor to bulk PdO formation is a distinct oxide phase that forms as small particles, referred to as PdO seeds, after the surface oxide saturates. With increasing oxygen coverage, the PdO seeds grow in size and eventually transform to more stable particles that agglomerate to yield a PdO film. Oxidation effectively ceases when the surface oxide layer is completely replaced by the bulk PdO film, demonstrating that the surface oxide is needed for PdO formation at the conditions studied. Both the kinetics of PdO formation and the final thickness of the PdO thin film depend strongly on the thermal stability of the PdO seeds. Below the decomposition temperature of the seeds (∼600 K), oxidation follows kinetics similar to Langmuirian adsorption and appears to be limited only by the rate of oxygen adsorption onto the surface oxide. In contrast, PdO formation above 600 K initially exhibits acceleratory kinetics, with the rates starting low but increasing steadily during the initial growth of PdO. We also observe a significant decrease in PdO(1 0 1) film thickness and improved crystallinity when oxidation is conducted below 600 K. We show that the trends observed in the oxidation kinetics and film thickness can be qualitatively explained within the context of a model in which the thermodynamic stability of PdO particles increases with increasing particle size and PdO seeds/particles coexist with a two-dimensional (2D) gas of oxygen atoms adsorbed on the surface oxide layer. This model suggests that the PdO particle-2D gas coexistence relation gives rise to three distinct growth regimes, namely, stable seed nucleation, metastable seed nucleation and oxygen dissolution into the subsurface where the latter is established at 2D gas coverages below the stability limit of a flat PdO surface.

Local structure in sub- and supercritical CO 2: A Voronoi polyhedra analysis study

The local structure of CO 2 along the liquid–gas coexistence curve and along the critical isochore is analyzed through the metric properties of the Voronoi polyhedra (VP) of the molecules, such as the volume, density, and asphericity of the VP as well as the radius of the vacancies between the molecules. The behaviour of these properties (i.e., their distributions as well as the associated average and fluctuation values) provides a clear evidence of the inhomogeneous character of the distribution of the CO 2 molecules in the system when the temperature becomes close the critical one.

A DUSTY COMPONENT TO THE GASEOUS DEBRIS DISK AROUND THE WHITE DWARF SDSS J1228+1040

We present ISAAC spectroscopy and ISAAC, UKIDSS and Spitzer Space Telescope broad-band photometry of SDSS J1228+1040 -- a white dwarf for which evidence of a gaseous metal-rich circumstellar disk has previously been found from optical emission lines. The data show a clear excess in the near- and mid-infrared, providing compelling evidence for the presence of dust in addition to the previously identified gaseous debris disk around the star. The infrared excess can be modelled in terms of an optically thick but geometrically thin disk. We find that the inner disk temperatures must be relatively high (~1700 K) in order to fit the SED in the near-infrared. These data provide the first evidence for the co-existence of both gas and dust in a disk around a white dwarf, and show that their presence is possible even around moderately hot (~22,000 K) stars.

Calculation of Solid−Liquid−Gas Equilibrium for Binary Systems Containing CO2

Two equations typically used for the pure-solid fugacity proved to be identical by selecting an appropriate relation for the pure-solid vapor pressure and the pure-liquid vapor pressure. On the basis of the pure-solid fugacity, a semipredictive model using solubility data (SMS) and a calculation model combining with GE models (CMG) were developed to calculate the solid−liquid−gas (SLG) coexistence lines of pure substances in the presence of CO2. For the SMS model, the Peng−Robinson equation of state (PR-EoS) with the van der Waals one-fluid mixing rule is used to correlate the solute solubility in CO2 to obtain the interaction parameter k12, which is further employed to predict the SLG coexistence lines by two methods: one adopts the fugacity coefficient of the solute in the liquid phase by an equation of state calculation (SMS-φ); the other uses the activity coefficient of the solute in the liquid phase calculated from the UNIFAC model (SMS-γ). For the CMG model, the PR-EoS with the linear combination of...

Correspondence between the Critical and the Zeno-Line Parameters for Classical and Quantum Liquids

We set new regularities between the effective compressibility factor at the critical point (Z*) and unit compressibility line (Zeno-line) parameters. For classical liquids, Z* is the ordinary compressibility factor Z(c), but for quantum liquids Z* depends on the de Boer parameters. As a result, we show that a wide group of real substances with the classical thermodynamical properties has Z(c) < 0.32. Classical mercury and quantum H(2), He(4), and He(3) have Z(c) or Z* > 0.37. Using the low temperature part of the liquid-gas coexistence curve obtained from experiment, we can find the critical parameters for metals (Al, Cu, W, U, and Zr) for which these parameters are unknown in advance and lie in the domain of parameters still inaccessible for experiment.

Steady-state molecular dynamics simulation of vapour to liquid nucleation with McDonald's dæmon

The most interesting step of condensation is the cluster formation up to the critical size. In a closed system, this is an instationary process, as the vapour is depleted by the emerging liquid phase. This imposes a limitation on direct molecular dynamics (MD) simulation of nucleation by affecting the properties of the vapour to a significant extent so that the nucleation rate varies over simulation time. Grand canonical MD with McDonald’s daemon is discussed in the present contribution and applied for sampling both nucleation kinetics and steady-state properties of a supersaturated vapour. The idea behind that approach is to simulate the production of clusters up to a given size for a specified supersaturation. In that way, nucleation is studied by a steady-state simulation. A series of simulations is conducted for the truncated and shifted Lennard-Jones fluid which accurately describes the fluid phase coexistence of noble gases and methane. The classical nucleation theory is found to overestimate the free energy of cluster formation and to deviate by two orders of magnitude from the nucleation rate below the triple point at high supersaturations.

Piezoelectric actuation of (GaN/)AlGaN/GaN heterostructures

A detailed analysis of the piezoelectric response of (GaN/)AlGaN/GaN heterostructures is reported. The electromechanical properties of two types of heterostructures with an Al content of 31% are compared. Only a single two-dimensional electron gas (2DEG) is formed for samples with thin GaN cap layers, while both a 2DEG and a two-dimensional hole gas coexist in the case of thick GaN caps. The lower GaN layer represents the mechanically supporting layer, while the AlGaN film, and in some cases an additional GaN cap layer, serves as the piezoelectrically active layers for actuation. The 2DEG (at the lower AlGaN/GaN interface) provides the conducting channel which was used as back electrode for the applied external voltage. Electroreflectance spectroscopy is applied in order to determine the electric field distribution across the whole structure as a function of the applied voltage. It is found that only a part of the modulation voltage drops across the active region. Piezoelectric force microscopy yields the field (voltage)-dependent actuation of the layers. By correlating the results of the two experimental techniques we are able to determine the piezoelectric modulus d33 with considerably improved reliability. A value for Al0.31Ga0.69N of 5 pm/V is found which is higher than an estimation based on previously reported data for GaN and AlN.

Effect of Particle Porosity on Hysteresis in Trickle-Bed Reactors

Hydrodynamics in trickle-bed reactors (TBRs) is quite complex because of the coexistence of gas−liquid−solid phases. Recent past hysteresis have been the subject of investigation to improve the understanding of the flow features at the microlevel, aiming to demystify the complex hydrodynamics. The purpose of the present study is to identify the role of particle porosity on hysteresis by choosing particles of different pore density (nonporous, semiporous, porous) but prepared from same material with identical shape and sizes. Experiments were carried out with industrial relevant-sized alumina extrudates in a 150 mm ID column using both a dry- and a wet-bed startup procedure. Comprehensive pressure drop hysteresis data were generated in increasing and decreasing modes of water flow in the presence of a constant flow of air at ambient condition. Pronounced but different magnitudes of pressure drop hysteresis were observed with all three types of particles at first cycle as well at subsequent cycle of operation. A deviation in pressure drop up to 90% was found between increasing and decreasing modes of operation, even after prewetting the bed. The same amount of hysteresis was observed for all the subsequent cycles, but the value is higher for particles with higher porosity. This confirms that particle porosity plays a major role in the existence of different flow texture at the microlevel in the trickle flow regime. This observation is reported here for the first time, and we believe that there is no such experimental data available in the literature. The genesis of this different hysteretic behavior of porous particles lies in the different ways liquid spreads/retracts over porous and nonporous particles. A conceptual framework of hysteresis proposed by Maiti et al. (2005), which is based on the concept of participating and nonparticipating particles and principles of liquid spreading on porous and nonporous substrates, is found to explain successfully the various features of hysteresis observed with all three types of particles. This study is expected to be useful to the TBR researcher and practitioner in enhancing the understanding further to demystify the complex hydrodynamic phenomena in TBRs.

Henry's law constant and related coefficients for aqueous hydrocarbons, CO 2 and H 2S over a wide range of temperature and pressure

This article presents three interrelated topics. First, the Henry's law constant (HLC) and its use are reviewed in a broader thermodynamic context reaching beyond the restricted image of HLC as a coefficient reflecting partitioning between liquid and vapor phases. The relationships of HLC to the vapor–liquid distribution coefficient and the air–water partition coefficient are discussed as well as the interrelation between expressions of HLC in terms of different concentration scales. Second, the previously published group contribution method for estimation of HLC of hydrocarbons [J. Sedlbauer, G. Bergin, V. Majer, AIChE J. 48 (2002) 2936] is extended by adding the newly determined parameters for CH 4, CO 2 and H 2S. Inclusion of these three major constituents of the natural gas makes the method more versatile in application to systems where oil and/or natural gas coexist with an aqueous phase. When establishing the parameters of the model the representative HLCs from literature were combined with the data on the derivative properties available over a wide range of conditions from the calorimetric and volumetric experiments. An attention is paid particularly to the effect of pressure on the HLC. Third, a convenient user-friendly software package is described allowing calculation of HLC and of other related coefficients over a wide range of temperature and pressure on the basis of the presented model. This package is available on request in an executable form on a shareware basis for non-commercial users.

The Many Streams of the Magellanic Stream

We present results from neutral hydrogen (H I) observations of the tip of the Magellanic Stream (MS), obtained with the Arecibo telescope as a part of the ongoing survey by the consortium for Galactic studies with the Arecibo L-band Feed Array. We find four large-scale, coherent H I streams, extending continuously over a length of 20°, each stream possessing different morphology and velocity gradients. The newly discovered streams provide strong support for the tidal model of the MS formation by Connors et al. (2006), who suggested a spatial and kinematic bifurcation of the MS. The observed morphology and kinematics suggest that three of these streams could be interpreted as a three-way splitting of the main MS filament, while the fourth stream appears much younger and may have originated from the Magellanic Bridge. We find an extensive population of H I clouds at the tip of the MS. Two-thirds of clouds have an angular size in the range 3.5'-10'. We interpret this as being due to thermal instability, which would affect a warm tail of gas trailing through the Galactic halo over a characteristic timescale of a few Myr to a few hundred Myr. We show that thermal fragments can survive in the hot halo for a long time, especially if surrounded by a <106 K halo gas. If the observed clumpy structure is mainly due to thermal instability, then the tip of the MS is at a distance of ~70 kpc. A significant fraction of H I clouds at the tip of the MS show multiphase velocity profiles, indicating the coexistence of cooler and warmer gas.

Characteristics and dynamic settings of the Central-east Asia multi-energy minerals metallogenetic domain

That more than 82 percent of proved sandstone-type uranium deposits coexist with proved oil-gas or coalfields in the world reflects the fact of coexistence and accumulation of multi-energy minerals including oil, gas, coal and uranium in the same basin. Especially, this phenomenon is most typical in the Central-east Asia energy basins. Across China, Mongolia and some central Asian countries, the giant Central-east Asia metallogenetic domain (CEAMD) stretches more than 6,000 km from Songliao Basin of China in the east to the Caspian Sea in the west. The multi-energy minerals distribution characteristics of the domain include: their spatial distribution is complicated and ordered; the ore-bearing horizon relates closely to the geographical region; the accumulation/mineralization and localization time is the same or close; the occurrence setting and accumulation/mineralization have close correlation; and they have rich provenance for all the minerals. All of these imply that they have close relations between each other under a unified geodynamic background. The exogenetic uranium mineralization process in CEAMD can be divided into five phases using time limits of 100 Ma, (50±2) Ma, 20±(2–4) Ma, 8–5 Ma. The major mineralization periods and their differences in each primary uranium-bearing basin are identical to the oil-gas accumulation and localization periods and phases in the same basin, and are also in response to regional tectonics and controlled in general by the regional geodynamic environment. For industrial application and commercial exploitation, it is suggested that an important period for coexistence, accumulation and localization of oil, gas, coal and uranium and their interaction mainly occur in the late/last and post basin evolution. Through generalized analysis and comparison of accumulation/mineralization environment of the energy basins in CEAMD, the authors propose that the relatively stable regional tectonic background and moderate (weaker) structural deformation probably are necessary for formation, coexistence and preservation of large and medium-scaled sandstone-type uranium ore deposits, oil-gas fields and coalfields, while basins in favor of coexistence and accumulation are those intracratonal, intermediary massif basins and corresponding reformed basins.

Calculation of Methane Hydrate Solubility in Marine Environment and Its Constraints on Gas Hydrate Occurrence

AbstractBesides appropriate temperature and pressure ranges, sufficient gas supply is necessary for gas hydrate crystallization within gas hydrate stability zone. In this article we formulate the calculation of methane solubility assuming hydrate plus‐aqueous solution plus free gas, hydrate plus‐aqueous solution, or aqueous solution plus free gas coexist at equilibrium. There are four fields of methane phase (free gas, dissolved gas, hydrate, and hydrate + free gas) in the diagram of methane solubility versus depth. The contents of hydrate and free gas at Sites 1249, 1250 and 997 are computed. Calculated hydrate contents are 10%~61% (13.5~72.4 mbsf) and 0.7%~1.9% (35~106.5 mbsf) in sediment pores at Site 1249 and at Site 1250, respectively. The layer of free gas, 22 m in thickness and ~2.4% in sediment pores, immediately occurs below the gas hydrate zone at these two sites. At Site 997, hydrate occurs from 202.4 to 433.3 mbsf occupying about 5%~7% of porosity. The free gas layer is ~80 m thick below the hydrate layer methane gas occupying about 0.2%~28% of sediment pore space.

Genetic Relationship between Natural Gas Dispersal Zone and Uranium Accumulation in the Northern Ordos Basin, China

Abstract: The Ordos Basin is well‐known for the coexistence of oil, natural gas, coal and uranium. However, there has been little research to discuss the genetic relationship between them. In this paper, a case study of the Zaohuohao area in Dongsheng, Inner Mongolia, China, is conducted to investigate the genetic relationship between the natural gas and the uranium accumulation. Fluid inclusion data from the uranium‐bearing sandstone samples indicate that the fluid inclusions formed in a gas‐water transition zone. Using the homogeneous temperatures of aqueous inclusions coeval with hydrocarbon‐bearing inclusions, combined with the buried history and paleo‐temperature data, the gas‐water transition zone reached the area at about 110 Ma. On the basis of this, the contents of Uranium (U) and Total Organic Carbon (TOC) of the samples were analyzed, and there was no obvious relation between them. With regard to the available data from both publications and this study, it is found that the U mineralization has a spatiotemporal accordance with the gas‐water dispersal zone. Thus, it is believed that the natural gas in the gas‐water zone is an effective reducer to the U‐bearing ground water abundant in oxygen, which is the main factor to U accumulation. This result can be used as the reference to the U mines predicting and prospecting.

509 気液対向二相流における限界流下流量に関する研究(環境とエネルギー)

Gas-liquid counter current flow is a flow pattern where gas and liquid co-exist and are flowing in the opposite direction. This affect happens when LOCA (Loss Of Coolant Accident) occurs in the light-water reactor. Elucidation of the mechanism of this affect is needed to perform the cooling of the core enough. In this study, I assume the situation that water level was formed by a limited coolant. A purpose of this study is to elucidate this phenomenon from an aspect of the air bubble secession. About water level, I tested it by three patterns of 50mm, 100mm and 200mm.

Pathogenesis, diagnosis and management of pneumorrhachis

Pneumorrhachis (PR), the presence of intraspinal air, is an exceptional but eminent radiographic finding, accompanied by different aetiologies and possible pathways of air entry into the spinal canal. By reviewing the literature and analysing a personal case of traumatic cervical PR after head injury, we present current data regarding the pathoanatomy, clinical and radiological presentation, diagnosis and differential diagnosis and treatment modalities of patients with PR and associated pathologies to highlight this uncommon phenomenon and outline aetiology-based guidelines for the practical management of PR. Air within the spinal canal can be divided into primary and secondary PR, descriptively classified into extra- or intradural PR and aetiologically subsumed into iatrogenic, traumatic and nontraumatic PR. Intraspinal air is usually found isolated not only in the cervical, thoracic and, less frequently, the lumbosacral regions but can also be located in the entire spinal canal. PR is almost exceptional associated with further air distributions in the body. The pathogenesis and aetiologies of PR are multifold and can be a diagnostic challenge. The diagnostic procedure should include spinal CT, the imaging tool of choice. PR has to be differentiated from free intraspinal gas collections and the coexistence of air and gas within the spinal canal has to be considered differential diagnostically. PR usually represents an asymptomatic epiphenomenon but can also be symptomatic by itself as well as by its underlying pathology. The latter, although often severe, might be concealed and has to be examined carefully to enable adequate patient treatment. The management of PR has to be individualized and frequently requires a multidisciplinary regime.