Shell (Japan)

Abstract The splitting of globules is an important phenomenon during the final stages of disintegration processes. Three basic types of deformation of globules and six types of flow patterns causing them are distinguished. The forces controlling deformation and breakup comprise two dimensionless groups: a Weber group N We and a viscosity group N Vi . Breakup occurs when N We exceeds a critical value ( N We ) crit . Three cases are studied in greater detail: (a) Taylor's experiments on the breakup of a drop in simple types of viscous flow, (b) breakup of a drop in an air stream, (c) emulsification in a turbulent flow. It is shown that ( N We ) crit depends on the type of deformation and on the flow pattern around the globule. For case (a) ( N We ) crit shows a minimum value ∼ 0.5 at a certain value of ( N Vi ) and seems to increase indefinitely with either decreasing or increasing ratio between the viscosites of the two phases. For case (b) ( N We ) crit varies between 13 and ∞, depending on N Vi and on the way in which the relative air velocity varies with time, the lowest value refers to the true shock case and N vi →0. For case (c) ( N We ) crit , which determines the maximum drop size in the emulsion, amounts to ∼1, and the corresponding values of N Vi appear to be small. A formula is derived for the maximum drop size.

Advances in magnetic resonance (MR) imaging over the past 2 decades have led to MR becoming an increasingly attractive imaging modality. With the growing number of patients treated with permanent implanted or temporary cardiovascular devices, it is becoming ever more important to clarify safety issues in regard to the performance of MR examinations in patients with these devices. Extensive, although not complete, ex vivo, animal, and clinical data are available from which to generate recommendations regarding the safe performance of MR examination in patients with cardiovascular devices, as well as to ascertain caveats and contraindications regarding MR examination for such patients. Safe MR imaging involves a careful initial patient screening, accurate determination of the permanent implanted or temporary cardiovascular device and its properties, a thoughtful analysis of the risks and benefits of performing the examination at that time, and, when indicated, appropriate physician management and supervision. This scientific statement is intended to summarize and clarify issues regarding the safety of MR imaging in patients with cardiovascular devices.

High-efficiency Cu2ZnSn(S,Se)4 solar cells are reported by applying In2S3/CdS double emitters. This new structure offers a high doping concentration within the Cu2ZnSn(S,Se)4 solar cells, resulting in a substantial enhancement in open-circuit voltage. The 12.4% device is obtained with a record open-circuit voltage deficit of 593 mV.

Abstract The current status and future perspectives of Cu(In 1−x Ga x )Se 2 (CIGS) solar cells and modules will be discussed in this paper. The conversion efficiencies of the state of the art laboratory‐scale CIGS solar cells exceeded 20%, which are comparable to those of crystalline Si solar cells. The requirements on the properties of CIGS absorbers to achieve such high efficiencies will be described. The CIGS modules are already commercially available based on two major CIGS deposition techniques such as co‐evaporation and selenization. The current status, problems, and prospects of co‐evaporation and selenization will also be discussed. High‐efficiency flexible CIGS solar cells with efficiencies similar to those fabricated on soda–lime glass (SLG) substrates have been achieved by developing a novel Na incorporation technique. Critical issues to demonstrate high‐efficiency flexible solar cells will also be discussed. Copyright © 2010 John Wiley & Sons, Ltd.

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTSynthesis and reaction chemistry of stable two-coordinate phosphorus cations (phosphenium ions)A. H. Cowley and R. A. KempCite this: Chem. Rev. 1985, 85, 5, 367–382Publication Date (Print):October 1, 1985Publication History Published online1 May 2002Published inissue 1 October 1985https://pubs.acs.org/doi/10.1021/cr00069a002https://doi.org/10.1021/cr00069a002research-articleACS PublicationsRequest reuse permissionsArticle Views2509Altmetric-Citations394LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail Other access optionsGet e-Alertsclose Get e-Alerts

Abstract Closed-loop reservoir management is a combination of model-based optimization and data assimilation (computer-assisted history matching), also referred to as ‘real-time reservoir management’, ‘smart reservoir management’ or ‘closed-loop optimization’. The aim is to maximize reservoir performance, in terms of recovery or financial measures, over the life of the reservoir by changing reservoir management from a periodic to a near-continuous process. The key sources of inspiration for our work are measurement and control theory as used in the process industry and data assimilation techniques as used in meteorology and oceanography. We present results of a numerical example to illustrate the scope for closed-loop water flooding using real-time production data under uncertain reservoir conditions. The example concerns a 12-well water flood in a channelized reservoir. Optimization was performed using a reservoir simulator with functionality for adjoint-based life cycle optimization under rate and pressure constraints. Data assimilation was performed using the ensemble Kalman filter. Applying an optimization frequency of respectively once per 4 years, once per 2 years, once per year and once per 30 days resulted in an increase of net present value (NPV) with 6.68, 8.29, 8.30 and 8.71% compared to a conventional reactive control strategy. Moreover, the results for the 30-day cycle were very close (0.15% lower NPV) to those obtained by open-loop optimization using the ‘true’ reservoir model. We illustrate that for closed-loop reservoir management with a fixed well configuration, the use of considerably different reservoir models may lead to near-identical results in terms of NPV. This implies that in such cases the essential information may be represented with a much less complex model than suggested by the large number of grid blocks in typical reservoir models. We also illustrate that the optimal rates and pressures as obtained by open- or closed-loop optimization are often too irregular to be practically applicable. Fortunately, just as is the case for the data assimilation problem, the flooding optimization problem usually contains many more control variables than necessary, allowing for optimization of long-term reservoir performance while maintaining freedom to perform short-term production optimization.

Abstract A fast simple method is given for calculating heat losses to cap and base rock in thermal reservoir simulators. The method can handle backflow of heat and cyclic temperature variations. Test comparisons against analytic results are given. The method gives remarkably accurate results on the test problems, considering its simplicity. Introduction In thermal reservoir simulations, it is necessary to calculate the heat loss from the reservoir to the surrounding environment, usually to the cap and base rock. A finite-difference calculation can become expensive, especially on computer storage, as the temperature profile can extend large distances into the overburden and underburden, requiring large numbers of grid blocks for its description. However, high accuracy in the solution of the heat loss calculations is not usually required in reservoir simulators owing to the uncertainty in cap and base rock thermal parameters. This paper describes an efficient semi-analytical method for the case where the one-dimensional linear heat conduction equation is adequate for the heat loss calculations. Semi-analytical methods have been used previously (1,2,3), and a study of the results given in these papers leads us to the following tentative conclusions:Conduction within the cap rock rapidly wipes out any sharp differences in temperature. Thus, the temperature in the cap rock varies smoothly, even for rather erratic changes at the interface.Longitudinal heat conduction in the cap rock can usually be neglected, because the Peclet number is normally high for reservoir floods(2).The most important physical features of the heat loss process are good descriptions of the boundary conditions at the interface and conservation of cap rock energy. The tail of the temperature distribution contains little energy and is relatively unimportant. These points suggest that the temperature profile into the cap or base rock can be adequately approximated by any reasonably flexible function containing a few parameters. If such a function could be made to fit the thermal diffusivity equation with appropriate boundary conditions, and the calculation of the parameters could be done in a simple fast fashion, the method would become extremely attractive further justification for such an approach is that high accuracy is not required, as the coefficient of thermal conduction of the cap and base rock is rarely known precisely. The Method We choose as the fitting function for the temperature profile into the cap or base rock: (Equation Available In Full Paper) θ is the temperature at the interface between the reservoir and the cap or base rock (the zero level has been defined at the initial interface temperature); p and q are the fitting parameters yet to be determined; d may be interpreted as the diffusion length and should be of order √kt where t is the time measured from the instant at which the interface temperature first begins to change. The deepest penetrating term in (1) is z2e−z/d, which has its maximum at z = 2d. Hence we choose for the diffusion length:

Since 1987 Perkinsus marinus has been the most important pathogen of the eastern oyster, Crassostrea virginica, in Chesapeake Bay because of its widespread distribution and persistence in low salinity areas. The pathogen became established on all oyster beds in the Chesapeake Bay as a result of natural spread during the consecutive drought years from 1985 to 1988 or by movement of infected oysters during the same period. Elevated salinities resulting from drought conditions and concomitant warm winters allowed P. marinus to proliferate in what were historically low salinity areas. Oyster mortality was high on most beds and landings of market oysters declined to record low levels in both Maryland and Virginia during the late 1980s and early 1990s. The seasonal periodicity of P. marinus is primarily controlled by temperature. Both prevalence and intensity of infections begin to increase in June as temperature increases above 20 degrees C and overwintering infections begin to proliferate. Maximum values of prevalence and intensity occur in September immediately following maximal summer temperatures. Infection regression occurs during winter and spring as temperature declines resulting in minimum prevalence and intensity values in April and May. Prevalence and intensity of P. marinus infections in oysters from the James River, VA, over a five year period were significantly correlated with temperature when temperature data were lagged three months. Temperature explained 39% of the variability in prevalence and 46% of the variability in intensity. The relationship between temperature and annual variability in P. marinus abundance is somewhat obscure, in part because of the difficulty separating salinity and temperature effect. Nonetheless, data from 1988 to 1994 from the James River, VA, suggest that abnormally warm winters have a more significant Impact on summer P. marinus abundance than abnormally cold winters. Salinity is the primary environmental factor that controls local distribution and intensity of P. marinus infections. Long-term oyster disease monitoring along a salinity gradient in the James River, VA, revealed a statistically significant relationship between salinity and P. marinus prevalence and intensity. P. marinus infections remain light in intensity and no oyster mortality results if salinity is consistently less than 9 ppt. However, infections may persist for years in low salinity areas. If summer/fall salinities range from 9 to 15 ppt some infections may progress to moderate and heavy intensity, but oyster mortality is relatively low. If summer/fall salinities are consistently greater than 15 ppt, moderate and heavy infections may be numerous and oyster mortality may be high. Field studies in the York River, VA, suggest that new P. marinus infections are acquired from July through early October, but peak infection acquisition occurs during late August and is correlated with oyster mortality. The early infection process in oysters and the role of zoospores in transmission dynamics in nature are poorly understood. No direct link between oyster defense mechanisms and control of P. marinus infections has been established. If oyster defense mechanisms do modulate P. marinus infections, the components have not been identified. There is little evidence to support the common perception that pollution is responsible for the dramatic increase in P. marinus abundance since 1985. Pathogen abundance is clearly correlated with salinity increases resulting from drought conditions in the late 1980s, although there may be subtle effects of toxicants or poor water quality on the host/parasite interaction.

Abstract By Steven Johnson New York, NY: Riverhead Books, 2010. 313 pp. ISBN 978‐1‐59448‐771‐2 Reviewed by Jim Tebbe

Water-absorbing rocks are formed from minerals that can hold water in their crystal structure or between grain boundaries. Such water absorption is often accompanied by a change in the crystal dimension that manifests itself as a swelling of the rock. Swelling is particularly pronounced in rocks containing phyllosilicates because of the ease with which these minerals hydrate; it is thus of geological and geotechnical relevance in shales, clay-rich soils and zeolitized tuffs. The model of hydration swelling that we present here is based on extended versions of the equations of poroelasticity and Darcy's transport law, which we derive using a non-equilibrium thermodynamics approach. Our equations account for the hydration reaction under the assumption that the reaction rate is fast in comparison with the rate at which hydraulic state changes are communicated through the rock, i.e. that local physico-chemical equilibrium persists. Using a finite-element scheme for solving numerically the governing equations of our model, we simulate the creep of shales during a routine swelling test and calculate the stress and strain distributions around wellbores drilled in shale formations that undergo swelling. We show that swelling effects promote tensile failure of the wellbore wall.

Abstract A preliminary theory is established for the stability of a viscoelastic layer sandwiched in an infinitely extended medium of another viscoelastic material when a compressive force is acting in a direction parallel with the layer. The instability is manifested by a folding of the layer. It is shown that in general there exists a lower and a higher critical load between which folding occurs at a finite rate with a dominant wavelength. This is the wavelength whose amplitude increases at the fastest rate. Special cases are also discussed in more detail such as that of a purely viscous layer in a viscous fluid, an elastic layer in a viscous fluid, a viscous layer in an elastic medium, and of two Maxwell materials. Results indicate that the ratio of the relaxation times of the two materials is an important parameter.

This paper presents a mathematical model of the bidding process that deals explicitly with the uncertainty of the bidders about the value of the subject of the auction. By dealing with this often ignored factor, it obtains equilibrium strategies and profits as a function of the number of bidders, the relative values they attach to the subject of the auction and their accuracy in estimating it. Models are developed for both highest-bid-wins and lowest-bid-wins auctions.

Abstract Liquid, supplied through a stationary tube to the inner part of a rotating cup widening toward a brim, flows viscously in a thin layer toward this brim and is then flung off, all by centrifugal action. The flow within this layer and the disintegration phenomena occurring beyond the brim have been studied, experimentally as well as theoretically. A formula has been derived for the thickness and for the radial velocity of the liquid layer within the cup, which proved to agree reasonably well with experimental results. Three essentially different types of disintegration may take place around and beyond the edge of the cup designated, respectively, by: (a) the state of direct drop formation; (b) the state of ligament formation; and (c) the state of film formation. Which one of these is realized depends upon working conditions. Transition from state (a) into (b), or of state (b) into state (c) is promoted by an increased quantity of supply, an increased angular speed, a decreased diameter of the cup, an increased density, an increased viscosity, and a decreased surface tension of the liquid. The experimental results have been expressed in relationships between relevant dimensionless groups. For the state of ligament formation a semiempirical relationship has been derived between the number of ligaments and dimensionless groups determining the working conditions of the cup. Results of drop-size measurements made for the state of ligament formation as well as for the state of film formation show that atomization by mere rotation of the cup is much more uniform than commonly achieved with pressure atomizers.

BACKGROUND AND PURPOSE: Therapeutic hypothermia is a potent neuroprotectant approved for cerebral protection after neonatal hypoxia-ischemia and cardiac arrest. Therapeutic hypothermia for acute ischemic stroke is safe and feasible in pilot trials. We designed a study protocol to provide safer, faster therapeutic hypothermia in stroke patients. METHODS: Safety procedures and 4°C saline infusions for faster cooling were added to the ICTuS trial (Intravascular Cooling in the Treatment of Stroke) protocol. A femoral venous intravascular cooling catheter after intravenous recombinant tissue-type plasminogen activator in eligible patients provided 24 hours cooling followed by a 12-hour rewarm. Serial safety assessments and imaging were performed. The primary end point was 3-month modified Rankin score 0,1. RESULTS: Of the intended 1600 subjects, 120 were enrolled before the study was stopped. Randomly, 63 were to receive hypothermia plus antishivering treatment and 57 normothermia. Compared with previous studies, cooling rates were improved with a cold saline bolus, without fluid overload. The intention-to-treat primary outcome of 90-day modified Rankin Score 0,1 occurred in 33% hypothermia and 38% normothermia subjects, odds ratio (95% confidence interval) of 0.81 (0.36-1.85). Serious adverse events occurred equally. Mortality was 15.9% hypothermia and 8.8% normothermia subjects, odds ratio (95% confidence interval) of 1.95 (0.56-7.79). Pneumonia occurred in 19% hypothermia versus 10.5% in normothermia subjects, odds ratio (95% confidence interval) of 1.99 (0.63-6.98). CONCLUSIONS: Intravascular therapeutic hypothermia was confirmed to be safe and feasible in recombinant tissue-type plasminogen activator-treated acute ischemic stroke patients. Protocol changes designed to reduce pneumonia risk appeared to fail, although the sample is small. CLINICAL TRIAL REGISTRATION: URL: http://www.clinicaltrials.gov. Unique identifier: NCT01123161.

Abstract Calculations are presented of reflection coefficients of plane longitudinal waves incident at oblique angles on boundary planes between elastic media. It is shown that the manner in which these reflection coefficients vary with the angle of incidence is strongly affected by the values of the Poisson's ratios of the two media. It appears that, contrary to a conclusion arrived at by Muskat and Meres, the reflection coefficient may vary appreciably with the angle of incidence in the range between O° and 30°. Possibilities of practical application of this phenomenon are discussed.

Abstract Three categories of dispersed clay are described for hydrocarbon-bearing sandstones using scanning electron microscopy and correlated to rock geological-petrophysical parameters commonly used in reservoir evaluation. Dispersed clays can occur in pores as (a) discrete (not intergrown) particles, pores as (a) discrete (not intergrown) particles, (b) intergrown crystal linings on pore walls, and (c) crystals bridging across pores. These different clay morphologies significantly affect sandstone porosity/permeability, capillary pressure curve and porosity/permeability, capillary pressure curve and associated pore-size distribution parameters, "shaliness" indicators from X-ray diffraction and Qv measurements. Introduction The increased utilization of scanning electron microscopy (SEM) and associated elemental detection systems (e.g., energy dispersive analysis of X-rays) has greatly expanded our knowledge of dispersed clay morphology and mode of occurrence in sandstone reservoir rocks. The marginal or questionably productive nature of particular hydrocarbon-bearing productive nature of particular hydrocarbon-bearing zones can be due to silicate clay crystals developed within rock pores in a manner adversely affecting fluid flow. Variations in clay crystal morphology can change a hydrocarbon zone from economically nonproductive to productive, and vice versa. In the past, the direct observation and description of this past, the direct observation and description of this important rock property was limited to petrographic microscope techniques. Recent technological advances in SEM, however, have enabled the petroleum geologist routinely to study rock mineral, textural, and pore-space properties at magnifications, resolution, pore-space properties at magnifications, resolution, and depth of focus far exceeding petrographic thin section capabilities. Several recent papers have described and discussed the importance of dispersed clays in sandstones. This paper defines "dispersed" clay as silicate clay minerals (e.g., kaolinite, illite, smectite, chlorite) developed within the rock pore system and generally attached to rock mineral surfaces. Dispersed clay in rocks is of diagenetic (i.e., authigenic) origin, having developed subsequent to sediment deposition by precipitation of clay crystals from pore fluids. Particular clay mineral species develop in response to changes in pore water chemistry brought about by changing pore water chemistry brought about by changing temperature, pressure and groundwater conditions during burial and compaction. Since dispersed clays generally occur as a rock pore-filling component and haze a variety of crystal sizes and shapes, they exhibit a broad spectrum of adverse effects on rock fluid flow and fluid saturation properties. This paper describes (a) three basic types of dispersed clay in sandstones and (b) several laboratory measured geological-petrophysical properties associated with each of these three clay types that are commonly used in evaluating hydrocarbon-bearing reservoirs. Specifically, sandstone samples are classified into three general categories on the basis of dispersed clay morphology as revealed by SEM. Each category is characterized by the following rock petrophysical parameters: porosity and air petrophysical parameters: porosity and air permeability, oil and water relative permeability, permeability, oil and water relative permeability, air/mercury capillary pressure curves, pore size and sorting, cation exchange capacity, and the amount of pore-filling clay estimated from X-ray diffraction and pore-filling clay estimated from X-ray diffraction and thin section analysis. DISPERSED CLAY CATEGORIES The basic criteria used to define and contrast the three general types of dispersed clay in sandstones are (a) clay crystal structure and (b) location on pore walls (i.e., mineral surfaces) and/or within intergranular pores and pore throats. Since the primary objective of this paper is to set forth the relationship of dispersed clay types to sandstone petrophysical properties, detailed discussions of petrophysical properties, detailed discussions of specific clay types and morphologies are not presented. The aforementioned Refs. 1 through 3 can presented. The aforementioned Refs. 1 through 3 can be referred to for this information. The three categories of dispersed clay are as follows.

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTRheological characterization of the gel point: a new interpretationRene Muller, Eric Gerard, Pascal Dugand, Paul Rempp, and Yves GnanouCite this: Macromolecules 1991, 24, 6, 1321–1326Publication Date (Print):March 1, 1991Publication History Published online1 May 2002Published inissue 1 March 1991https://pubs.acs.org/doi/10.1021/ma00006a017https://doi.org/10.1021/ma00006a017research-articleACS PublicationsRequest reuse permissionsArticle Views2201Altmetric-Citations120LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail Other access optionsGet e-Alertsclose Get e-Alerts

In order to demonstrate experimentally that the competition between the antiferroelectric and ferroelectric interactions stabilizing Sm${\mathit{C}}_{\mathit{A}}^{\mathrm{*}}$ and Sm${\mathit{C}}^{\mathrm{*}}$ (the pairing energy of the transverse dipole moments in adjacent smectic layers and the packing entropy resulting from the excluded volume effect) produces a variety of antiferroelectric and ferroelectric subphases in the temperature region between antiferroelectric Sm${\mathit{C}}_{\mathit{A}}^{\mathrm{*}}$ and ferroelectric Sm${\mathit{C}}^{\mathrm{*}}$, we have tried to observe the subphases in several binary mixtures of chiral smectic liquid crystals. The subphases were identified by the electric field dependence of cono- scopic figures and the apparent tilt angle as a function of field strength. Systematically changing the mixing ratio of two properly chosen compounds and studying the stability of each subphase, we have substantiated that the subphases between Sm${\mathit{C}}_{\mathit{A}}^{\mathrm{*}}$ and Sm${\mathit{C}}^{\mathrm{*}}$ form a Devil's staircase, Sm${\mathit{C}}_{\mathit{A}}^{\mathrm{*}}$(${\mathit{q}}_{\mathit{T}}$). Here, ${\mathit{q}}_{\mathit{T}}$ is an irreducible rational number, which specifies a fraction of the ferroelectric ordering in the antiferroelectric ordering. We have also discussed the relationship of Sm${\mathit{C}}_{\mathit{A}}^{\mathrm{*}}$(${\mathit{q}}_{\mathit{T}}$) to the other staircase, Sm${\mathit{C}}_{\mathrm{\ensuremath{\alpha}}}^{\mathrm{*}}$(${\mathit{q}}_{\mathit{T}}$), that was proposed to exist as a result of the rather macroscopic, electrostatic interaction among two-dimensional spontaneous polarizations in smectic layers.

Summary Open literature and new experimental compaction data from five reservoir and 16 outcrop sandstones are used to delineate the near-elastic, inelastic, and failure domains in 3D-stress space for porosity classes of 5 to 15%, 15 to 25%, and 25 to 35%. Applications of this compaction-domain model include the analysis of the extent of the near-elastic domain (where elasticity theory can be used to describe and predict rock deformation), the pore-volume compressibility (Cpp), and the permeability reduction as a function of reservoir stress path. This is illustrated for a well-consolidated sandstone reservoir with an average porosity of approximately 18%. Two aspects of dynamic reservoir modeling in the near-elastic domain are addressed: calculation of Cpp from raw volumetric-compaction data as a function of isotropic total stress change, and the correction of Cpp for a nonhydrostatic reservoir stress path. Open-literature work combined with our experimental data indicates that the compaction-induced permeability reduction of 15 to 25% porosity sandstone in the near-elastic domain depends predominantly on the increase of the effective mean stress, not on the reservoir stress path.

To resolve the taxonomic status of a small cupped oyster from southern China, we collected and sequenced oysters from 20 sites in China along with sister species from other parts of the world. A total of 187 oysters were sequenced for 2 fragments belonging to the mitochondrial 16S rRNA and cytochrome oxidase I (COI) genes. Sequence analyses of both gene fragments indicate that the small cupped oyster from southern China is the same species as Crassostrea angulata from Portugal. C. angulata has a wide distribution in southern China, ranging from Zhejiang to Hainan, with the Yangtze River separating it from Crassostrea gigas in northern China. The wide distribution and high gene diversity in China support the suggestion of a historical transfer of C. angulata from China to Europe. Sequence divergence between C. angulata and C. gigas, 1.05–1.32% in 16S and 2.22–3.37% in COI, is higher than that between the most divergent populations of a Crassostrea species (C. virginica, 0.51% in 16S and 2.04–2.22% in COI), but considerably lower than that observed between two closely related sister species (2.11–2.37% in 16S and 9.32–10.11 % in COI, between C. gigas and Crassostrea sikamea). This finding and the fact that the two oysters live in the same region with slightly different biological characters but can hybridize without any difficulties suggest that C. angulata should be considered a subspecies of C. gigas.