Primary and secondary controls on reservoir quality: relationships between lithofacies and the development of deformation bands

Primary sedimentological processes in mixed eolian-fluvial systems can result in lithological variability at the sub-seismic scale. This variation in genetic origin has a direct control on the porosity and permeability of a body of sediment, with variations in lithofacies types, their assemblages and contacts responsible for creating fluid pathways or baffles. Post-depositional near-surface and deep process diagenesis affects original porosity and permeabilities through mineral dissolution and re-precipitation, and the generation of stress induced fractures. Examination of bedrock exposure and drillcore from the depositionally heterogeneous Triassic Sherwood Sandstone of north-west England demonstrates that there is a strong facies control on the presence and type of secondary processes, namely in the form of deformation bands. This is despite the entire range of lithofacies being subject to the same regional and local stresses. The mixed eolian-fluvial Sherwood Sandstone Group exhibits a wide range of facies types which allows a good insight in to those most susceptible to deformation band formation. Preliminary work indicates that the eolian grainfall and grainflow facies types are at most risk of being host to deformation bands above all other facies types (both eolian and fluvial). This is significant as both of these facies have very good permeabilities in excess of 6000 mD (millidarcy), whilst the deformation bands have significantly less ranging from 0.1-10 mD. The deformation bands are also identified to occur in a range of styles that vary from: i) isolated thin (1-2 mm thick) individual seams, ii) complex conjugate interlocking sets, and iii) chaotic thick amalgamations of multiple deformation bands ranging from 5-120 cm thick. Each of the deformation types has been constrained in three dimensions and a range of idealised conceptual models are presented that indicate the potential of effects on reservoir quality

Architectural analysis of a Triassic fluvial system: the Sherwood Sandstone of the East Midlands Shelf, UK

The Sherwood Sandstone Group of the northeast UK (East Midlands Shelf) has hitherto never been studied in detail to ascertain its palaeoenvironment of deposition, largely because it is poorly exposed. As such, this paper aims to provide the first modern sedimentological interpretation of the Sherwood Sandstone in the east of England based on a field outcrop at the disused quarry at Styrrup. This is in stark contrast to the western parts of England where the Sherwood Sandstone is well exposed and offshore in the North Sea Basin where it is represented by a substantial library of core material where it is also relatively well understood. The outcrop at Styrrup Quarry allows contrasts to be made with the style and expression of the Sherwood Sandstone between eastern and western England. Specifically, this highlights differences around the variation in fluvial discharge (between lowstand and highstand) and the absence of aeolian facies types. It is interpreted that these differences relate to discharge variations between ephemeral and perennial systems with a perennial model proposed for Styrrup Quarry. This model draws upon inferences of additional water input from more local areas, likely topographic uplands of the London–Brabant and Pennine Highs which supplement the primary source of the Variscan Mountains in France with additional water and sediment

Three-dimensional stratigraphic complexity within mixed Eolian-Fluvial successions: implications for reservoir connectivity

On-going exploration of conventional hydrocarbon plays is increasingly focused towards the development of geologically complex reservoirs for which stratigraphic heterogeneity is difficult to predict. Many such current reservoirs, and an increasing proportion of likely future ones, are characterized by sedimentary bodies that accumulated as mixed eolian-fluvial systems that competed and interacted synchronously. Well-known reservoir examples include the Permian Unayzah Formation of Saudi Arabia, the Permian Rotliegend Group of the North Sea, the Triassic Ormskirk Sandstone of the East Irish Sea, the Jurassic Norphlet Sandstone of the Gulf of Mexico, and the Cretaceous Agrio Formation, Argentina. These mixed depositional systems typically exhibit highly variable lateral and vertical facies configurations that preserve complex juxtapositions of architectural elements composed of stratal units with markedly variable reservoir properties. Such stratigraphic partitioning is intrinsically difficult to predict from limited subsurface data. As such, there exists a requirement for more sophisticated geological models to better account for reservoir architecture and connectivity. This work uses outcropping case-study examples of eolian-fluvial interactions from the Triassic Sherwood Sandstone Group of the UK and the Permo-Pennsylvanian Cutler Group of southeast Utah, USA, to develop a suite of predictive models that depict common styles of stratigraphic complexity within eolian-fluvial systems. Studied successions accumulated in response to a variety of system interactions, deposits of which are preserved at a range of spatial scales from 100–104 m: (i) short-lived and localized fluvial reworking of eolian dune deposits in response to flash flood events; (ii) eolian reworking of fluvial deposits via winnowing; (iii) the fluvial exploitation and possible damming of open interdune corridors; (iv) the flooding of isolated (spatially enclosed) interdune hollows in response to an elevated water table. Identified types of interactions are characterized within a spatial scheme whereby occurrences can be used as a predictor of relative position within the larger-scale zone of transition between coeval eolian dune-field and fluvial systems. Application of this spatial scheme allows for prediction of the type of eolian-fluvial interactions expected for a range of paleogeographic settings, thereby serving as a tool for ranking exploration targets within larger prospect areas

PyEvolve: a toolkit for statistical modelling of molecular evolution

BACKGROUND: Examining the distribution of variation has proven an extremely profitable technique in the effort to identify sequences of biological significance. Most approaches in the field, however, evaluate only the conserved portions of sequences – ignoring the biological significance of sequence differences. A suite of sophisticated likelihood based statistical models from the field of molecular evolution provides the basis for extracting the information from the full distribution of sequence variation. The number of different problems to which phylogeny-based maximum likelihood calculations can be applied is extensive. Available software packages that can perform likelihood calculations suffer from a lack of flexibility and scalability, or employ error-prone approaches to model parameterisation. RESULTS: Here we describe the implementation of PyEvolve, a toolkit for the application of existing, and development of new, statistical methods for molecular evolution. We present the object architecture and design schema of PyEvolve, which includes an adaptable multi-level parallelisation schema. The approach for defining new methods is illustrated by implementing a novel dinucleotide model of substitution that includes a parameter for mutation of methylated CpG's, which required 8 lines of standard Python code to define. Benchmarking was performed using either a dinucleotide or codon substitution model applied to an alignment of BRCA1 sequences from 20 mammals, or a 10 species subset. Up to five-fold parallel performance gains over serial were recorded. Compared to leading alternative software, PyEvolve exhibited significantly better real world performance for parameter rich models with a large data set, reducing the time required for optimisation from ~10 days to ~6 hours. CONCLUSION: PyEvolve provides flexible functionality that can be used either for statistical modelling of molecular evolution, or the development of new methods in the field. The toolkit can be used interactively or by writing and executing scripts. The toolkit uses efficient processes for specifying the parameterisation of statistical models, and implements numerous optimisations that make highly parameter rich likelihood functions solvable within hours on multi-cpu hardware. PyEvolve can be readily adapted in response to changing computational demands and hardware configurations to maximise performance. PyEvolve is released under the GPL and can be downloaded from http://cbis.anu.edu.au/software webcite

Using core and outcrop analogues to predict flow pathways in the subsurface: examples from the Triassic sandstones of north Cheshire, UK

Borehole core provides detailed vertical data which is used to interpret subsurface sand body architectures, but assumptions are made on the relationship between the lateral and vertical thickness, and the interconnectivity of units. The sedimentological complexity of the Sherwood Sandstone Group succession in this area, passing between aeolian and fluvial packages creates local- to regional-scale heterogeneities which will impact flow pathways within the rockmass. Measured thickness in boreholes might represent an architectural element's true maximum thickness or more likely, a partial thickness as a result of incision by overlying facies types or as a result of the borehole sitting towards the margins of individual elements (e.g. tapering margin of channel elements). Length and thickness data were measured from a suite of primary core data and secondary published outcrop studies in north-west England. The addition of outcrop studies in combination with the borehole data provides a dataset from which the likely lateral extent of the architectural frameworks within the Triassic sandstones can be extrapolated. The interpreted high resolution sub-seismic architecture contributes to an increased understanding of flow pathways and the effect these may have on groundwater as well as sustainable energy technologies such as low-temperature geothermal aquifers, carbon storage and energy storage

A Statement of the principles and objects of a proposed national society for the cure and prevention of pauperism, by means of systematic colonization.

Original work held in Special Collections, Rare Books, 325.342 W14s

Africa’s oesophageal cancer corridor: geographic variations in incidence correlate with certain micronutrient deficiencies

Background The aetiology of Africa’s easterly-lying corridor of squamous cell oesophageal cancer is poorly understood. Micronutrient deficiencies have been implicated in this cancer in other areas of the world, but their role in Africa is unclear. Without prospective cohorts, timely insights can instead be gained through ecological studies. Methods Across Africa we assessed associations between a country’s oesophageal cancer incidence rate and food balance sheet-derived estimates of mean national dietary supplies of 7 nutrients: calcium (Ca), copper (Cu), iron (Fe), iodine (I), magnesium (Mg), selenium (Se) and zinc (Zn). We included 32 countries which had estimates of dietary nutrient supplies and of better-quality GLOBCAN 2012 cancer incidence rates. Bayesian hierarchical Poisson lognormal models were used to estimate incidence rate ratios for oesophageal cancer associated with each nutrient, adjusted for age, gender, energy intake, phytate, smoking and alcohol consumption, as well as their 95% posterior credible intervals (CI). Adult dietary deficiencies were quantified using an estimated average requirements (EAR) cut-point approach. Results Adjusted incidence rate ratios for oesophageal cancer associated with a doubling of mean nutrient supply were: for Fe 0.49 (95% CI: 0.29–0.82); Mg 0.58 (0.31–1.08); Se 0.40 (0.18–0.90); and Zn 0.29 (0.11–0.74). There were no associations with Ca, Cu and I. Mean national nutrient supplies exceeded adult EARs for Mg and Fe in most countries. For Se, mean supplies were less than EARs (both sexes) in 7 of the 10 highest oesophageal cancer ranking countries, compared to 23% of remaining countries. For Zn, mean supplies were less than the male EARs in 8 of these 10 highest ranking countries compared to in 36% of other countries