Modelling in-situ upgrading of heavy oil using operator splitting method

The in-situ upgrading (ISU) of bitumen and oil shale is a very challenging process to model numerically because of the large number of components that need to be modelled using a system of equations that are both highly non-linear and strongly coupled. Operator splitting methods are one way of potentially improving computational performance. Each numerical operator in a process is modelled separately, allowing the best solution method to be used for the given numerical operator. A significant drawback to the approach is that decoupling the governing equations introduces an additional source of numerical error, known as the splitting error. The best splitting method for modelling a given process minimises the splitting error whilst improving computational performance compared to a fully implicit approach. Although operator splitting has been widely used for the modelling of reactive-transport problems, it has not yet been applied to the modelling of ISU. One reason is that it is not clear which operator splitting technique to use. Numerous such techniques are described in the literature and each leads to a different splitting error. While this error has been extensively analysed for linear operators for a wide range of methods, the results cannot be extended to general non-linear systems. It is therefore not clear which of these techniques is most appropriate for the modelling of ISU. In this paper, we investigate the application of various operator splitting techniques to the modelling of the ISU of bitumen and oil shale. The techniques were tested on a simplified model of the physical system in which a solid or heavy liquid component is decomposed by pyrolysis into lighter liquid and gas components. The operator splitting techniques examined include the sequential split operator (SSO), the Strang-Marchuk split operator (SMSO) and the iterative split operator (ISO). They were evaluated on various test cases by considering the evolution of the discretization error as a function of the time-step size compared with the results obtained from a fully implicit simulation. We observed that the error was least for a splitting scheme where the thermal conduction was performed first, followed by the chemical reaction step and finally the heat and mass convection operator (SSO-CKA). This method was then applied to a more realistic model of the ISU of bitumen with multiple components, and we were able to obtain a speed-up of between 3 and 5.     

Species richness of the genus Molgolaimus (Nematoda) from local to ocean scale along continental slopes

This study investigated the distribution of Molgolaimus species (Nematoda) at different hierarchical spatial scales and observed the turnover of species along bathymetrical transects and among transects in two separate geographical regions. Samples from six transects (200–2000 m) from the Southern Oceans (SO) and four bathymetric transects (50–2000 m) from the Western Indian Ocean (WIO) were compared. Of the 30 species recorded, only one was common to both regions. WIO had higher local species richness than the SO. In both regions, the local scale was the greatest contributor to the total species richness. In the SO, there was no difference between species turnover at the different spatial scales, however, in the WIO, the turnover along bathymetrical transects was higher than among separated transects. For the particular genus studied, the evidence suggests that the study area in WIO has more widespread species and was better sampled, while the SO has many restricted species and it is most probably characterized by different biogeographical provinces. At the ocean scale (i.e. WIO versus SO), evolutionary histories may have strongly influenced nematodes species composition, while at local and regional scales, ecological processes are probably promoting species co‐existence and speciation. The high co‐existence of certain species at local scale is partially explained by species preference for different sediment layers.     

A comparison of ozone and chlorine toxicity to three life stages of the American oyster Crassostrea virginica

The effects of ozone-produced oxidants (OPO) on three developmental stages of the American oyster, Crassostrea virginica, were evaluated. Both straight-hinge (48-h post fertilisation) and setting pediveliger larvae were exposed to a series of OPO concentrations ranging from 0·05 to 0·30 mg/litre OPO (as total residual chlorine) at 25°C for 96 h. Mortality was used as the response parameter and results were quantitatively compared with the effects of chlorine-produced oxidants (CPO) obtained from the literature on these same developmental stages. Adult oysters (2- to 4-year class) were exposed to OPO concentrations ranging from 0·01 to 0·50 mg/litre at 15°C for 5 days and to the same concentration range at 25°C for two consecutive 6-day periods. Shell deposition and faecal matter accumulation were used as the response parameters for this stage.Straight-hinge larvae were significantly more sensitive to OPO than setting pediveliger larvae. Both larval stages were significantly more sensitive to CPO than to OPO. Shell deposition was significantly inhibited at all OPO concentrations for both 15°C and 25°C acclimated adult oysters. No significant differences were found between the shell deposition response of oysters at the two acclimation temperatures. Faecal matter accumulation was significantly reduced at OPO concentrations ≥ 0·05 mg/litre at both 15°C and 25°C. It was significantly (p < 0·05) greater for 25°C acclimated oysters than for 15°C acclimated oysters at OPO concentrations < 0·10 mg/litre but not at higher concentrations.     

Oceanic double-infusion: introduction

Double-diffusion, the mixing of fluids with two constituents of different molecular diffusivities, was originally discovered in the mid-1800s, forgotten, then rediscovered as an ‘oceanographic curiosity’ a century later. Many oceanographers suspect that double-diffusion has major effects on oceanic water masses and circulation, but direct measurement of the effects has proven difficult. In 1996, a Working Group was formed under the auspices of the Scientific Committee on Ocean Research (SCOR WG108), with the goal to identify progress and barriers to quantifying oceanic double-diffusive fluxes, and make recommendations for further progress. This document gives a brief history of double-diffusion, a review of evidence of its potential effects in the ocean, and gives an overview of the review articles contained in this volume, written by the Working Group members with the above aim in mind.     

Occurrence of roll circulations in a shallow boundary layer

Meteorological measurements taken at the Näsudden wind turbine site during slightly unstable conditions have been analyzed. The height of the convective boundary layer (CBL) was rather low, varying between 60 and 300 m. Turbulence statistics near the ground followed Monin-Obukhov similarity, whereas the remaining part of the boundary layer can be regarded as a near neutral upper layer. In 55% of the runs, horizontal roll vortices were found. Those were the most unstable runs, with -z _i/L > 5. Spectra and co-spectra are used to identify the structures. Three roll indicators were identified: (i) a low frequency peak in the spectrum of the lateral component at low level; (ii) a corresponding increase in the vertical component at mid-CBL; (iii) a positive covariance {ovvw} together with positive wind shear in the lateral direction (V/z) in the CBL. By applying these indicators, it is possible to show that horizontal roll circulations are likely to be a common phenomenon over the Baltic during late summer and early winter.     

Kinetic rate laws derived from order parameter theory IV: Kinetics of Al,Si disordering in Na-feldspars

The kinetic rate laws of Al-Si disordering under dry conditions (T = 1353K, 1253 K, 1223 K, 1183 K) and in the presence of water (p = 1 kbar, T = 1023 K, 1073 K, 1103 K) were studied both experimentally and theoretically. A gradual change of the degree of order was found under dry conditions. For intermediate degrees of order broad distributions of the order parameter Q _od occur. The variations of Q _od are correlated with structural modulations as observed in the transmission electron microscope. The time evolution of the mean value of Q _od can be well described by the rate law: $$\frac{{dQ_{od} }}{{dt}} = - \frac{\gamma }{{RT}}\exp \sum\limits_{i = 1}^n {X_i^2 } \left[ {\frac{{ - (G_a^0 + \varepsilon (\Delta Q_{od} )^2 )}}{{RT}}} \right]\frac{{dG}}{{dQ_{od} }}$$ with the excess Gibbs energy G and G _a ⁰ = 433.8 kJ/mol, ?= -27.4 kJ/mol, γ = 1.687 · 10¹⁴ h ^?1. Under wet conditions, two processes were found which occur simultaneously. Firstly, some material renucleated with the equilibrium degree of order. Secondly, the bulk of the material transformed following the same rate law as under dry conditions but with the reduced activation energy G _a ⁰ = 332.0 kJ/mol and ? = -43.0 kJ/ mol, γ = 1.047 · 10¹³ h^?1. The applicability of the kinetic theory is discussed and some ideas for the analysis of geological observations are evolved.     

Tracking hydrological responses of a thermokarst lake in the Old Crow Flats (Yukon Territory,Canada) to recent climate variability using aerial photographs and paleolimnological methods

Recent studies using remote sensing analysis of lake‐rich thermokarst landscapes have documented evidence of declining lake surface area in response to recent warming. However, images alone cannot identify whether these declines are due to increasing frequency of lake drainage events associated with accelerated thermokarst activity or to increasing evaporation in response to longer ice‐free season duration. Here, we explore the potential of combining aerial photograph time series with paleolimnological analyses to track changes in hydrological conditions of a thermokarst lake in the Old Crow Flats (OCF), Canada, and to identify their causes. Images show that the water level in lake OCF 48 declined markedly sometime between 1972 and 2001. In a sediment core from OCF 48, complacent stratigraphic profiles of several physical, geochemical, and biological parameters from ～1874–1967 indicate hydro‐limnological conditions were relatively stable. From ～1967–1989, declines in organic matter content, organic carbon isotope values, and pigment concentrations are interpreted to reflect an increase in supply of minerogenic sediment, and subsequent decline in aquatic productivity, caused by increased thermo‐erosion of shoreline soils. Lake expansion was likely caused by increased summer rainfall, as recorded by increased cellulose‐inferred lake‐water oxygen isotope compositions. Stratigraphic trends defining the lake expansion phase terminated at ～1989, which likely marks the year when the lake drained. Above‐average precipitation during the previous year probably raised the lake level and promoted further thermo‐erosion of the shoreline soils that caused the lake to drain. These are meteorological conditions that have led to other recent lake‐drainage events in the OCF. Thus, the decline in lake level, evident in the aerial photograph from 2001, is unlikely to have been caused by evaporation, but rather is a remnant of a drainage event that took place more than a decade earlier. After drainage, the lake began to refill, and most paleolimnological parameters approach levels that are similar to those during the stable phase. These findings indicate that combined use of aerial images and paleolimnological methods offers much promise for identifying the hydrological consequences of recent climatic variations on thermokarst lakes. Copyright © 2011 John Wiley & Sons, Ltd.     

A Last Glacial Maximum pollen record from Bodmin Moor showing a possible cryptic northern refugium in southwest England

A late Devensian palynological record is presented from Dozmary Pool (Bodmin Moor, southwest England), beyond the southern limit of the Last Glacial Maximum (LGM) British Ice Sheet. The pollen assemblages indicate predominantly herbaceous tundra–steppe communities but also include elevated levels (typically 10–20%) of conifer tree pollen (Picea, Pinus, Abies) and lower but persistent percentages of broadleaf tree pollen during the LGM. This record is seemingly at odds with the orthodox view of an entirely treeless tundra–steppe environment for this region and elimination of tree species from the British Isles during glacial maxima. Long‐distance pollen transport seems an unlikely explanation for the tree pollen considering distance to the nearest known refugia, except possibly for Pinus. Reworking of the tree pollen, often invoked in these circumstances, remains a possible alternative, especially given the abundance of these trees in the region during early Devensian interstadials. However, this explanation has been challenged by studies reporting plant macrofossil and faunal evidence for survival of temperate biota during glacial maxima and from climate modelling work that suggests some trees could have survived the glacial extremes in areas well beyond the recorded glacial refugia. Assuming reworking was not a major factor, the Dozmary Pool pollen record is consistent with the ‘cryptic northern refugia hypothesis’ that invokes survival of trees in small, scattered populations under locally favourable conditions during glacial maxima. Copyright © 2009 John Wiley & Sons, Ltd.     

Nematode diversity and its relation to the quantity and quality of sedimentary organic matter in the deep Nazaré Canyon,Western Iberian Margin

Samples collected in the deep Nazaré Canyon and at the adjacent slope, during the HERMES RRS Discovery D297 cruise (2005), were analysed for metazoan meiofauna, nematode structure and diversity and its relation to quality and quantity of sedimentary organic material. The amount and quality of organic matter available for direct consumption was much higher in the canyon compared to the slope and positively correlated with high nematode abundances (795–1171 ind. 10 cm^?2) and biomass (93.2–343.5 μg dry weight 10 cm^?2), thus leading to higher standing stocks. Canyon nematode assemblages also showed particular adaptations (e.g. higher trophic complexity, variability of nematode morphology, and presence of opportunistic genera) to canyon conditions, particularly in the deeper sediment layers. The Nazaré Canyon's nematode diversity was slightly lower than that of the adjacent slope and its assemblages were characterised by a higher dominance of certain genera. Still, the canyon contributes considerably to total Western Iberian Margin diversity due to different assemblages present compared to the slope. Furthermore, the harsh conditions in terms of hydrodynamic disturbance and the high organic matter flux are likely to have a negative impact on the establishment of species rich meiobenthic communities, especially in the canyon axis.